The human genetic disorder, Neurofibromatosis Type 1 (NF1), by virtue of its wellstudied variability and complexity, presents a compelling opportunity to examine the relationships of genotypes and phenotypes in general. A new concept, the praxitype, is introduced as a means of designating and accounting for the complex biochemical and genetic interactions interposed between the canonical genotype and phenotype.

Riccardi VM (2015) NF1 and the Praxitype. JSM Genet Genomics 2(1): 1006.

• Genotype
• Homology
• Neurofibromatosis Type 1
• NF1
• Phenotype
• Praxitype
• Supergene 

CT: Contagion; ED: Epidemic Disease; IA: Infectious Agent; γ: Genotype; φ: Phenotype; π: Praxitype

Classical genetics at all levels through to modern medical genetics has relied on two phrases to deal with the relationship of the heritable element – DNA – to its biochemical, cellular, tissue, organ and organismal consequences. These two phrases are genotype and phenotype and they have been used as though the relationship between them is obvious and singular. I would posit that this simplification, usually implicitly ignored or skirted, now needs to be investigated carefully and, as an element thereof, displaced by a concept and phrase commensurate with the etymology and utility of the original two phrases/concepts, namely genotype and phenotype [1]. To this end, I propose the term, praxitype, a word that literally allows for and designates the practice or mechanism by which phenotype elements derive from genotypes. In short, praxitype goes beyond allowing to absolutely requiring a specific combination of mechanisms or modalities by which the phenotype derives from the genotype [2].

How the DNA code is rendered as a specific phenotype we know to be extraordinarily complex for at least selected gene loci, not the least of which is NF1 [3-6].Yesteryear’s “Central Dogma” schema (DNA → RNA →Protein) has served its purpose and it is now time to consider more exactly the multiple schemata that contribute to translating chromosomally-organized DNA to biochemical, cellular, tissue, organ and organismal phenotypes. [2;7] It is not my intention either to itemize or to characterize each of the schemata. Rather, I wish to establish that there is indeed a category of such phenomena, the recognition of which will facilitate – even foment – establishment of a hierarchy of these phenomena. That category is the praxitype. At the outset, I expect that each genetic locus will have a prototypic praxitype, with alternative, subordinate praxitypes employed as a function of factors yet to be determined.

As a noun, the word, practice, is commonly defined as “the actual application or use of an idea, belief or method, as opposed to the theories about such application or use.” (Google Online, 23 September 2014) Alternatively, as a verb, practice is defined as the ability to “carry out or perform a particular activity, method or custom habitually or regularly.” (Google Online, 23 September 2014) Ultimately, these definitions derive etymologically from the Greek verb “prasso” (πρασσω), “to achieve, bring about, effect, accomplish.” (Wikipedia, 23 September 2014) From a genetic vantage point, the genotype (γ) literally encodes certain details about what is to be accomplished, the latter traditionally referred to as the phenotype (φ). What has been left out is the sum of practices (or practices as this verb is spelled in British parlance) that translate or transform the γ code variously into one or more φ. The key is that there are multiple (types of) practices that influence the transformation, for example, transcriptional editing, post-translational modifications, imprinting, the influences of miRNA and lncRNA, and the direct and indirect interactions with other gene loci and their peptide/protein products. Again, the sum of these practices, that is, the praxitype (π), is more or less distinctive for each locus, such that the full spectrum of a φ depends as much on the π of the locus as on its γ. The NF1 gene locus demonstrates this principle exquisitely, [8;9] especially when its γ has been altered (mutated or deleted) [8- 12]. A mutated NF1 γ restricts and/or expands the π distinctively for each mutation’s φ. Being able to itemize the elements of both the π typical of the wildtype γ and the π typical of various classes of mutant NF1 γ is likely critical for understanding the molecular pathogenesis of the NF1 syndrome in terms of it multiple features, consequences and complications [13].

Very large genes with multiple domains are likely to have a comparably complex praxitype (or set of praxitypes). The NF1 gene almost certainly is representative of this consideration.[14] More generally, perhaps the notion of “supergenes” will be more amenable to explication through the application of the praxitype concept [15]. Supergenes were originally considered to account for mimicry [16] and homology, [14;17-19] but more recently for ordinary developmental phenomena[7;20] and cancer [2]. In these regards, a brief consideration of homology and related issues may be helpful in elucidating praxitypes.

Homology, Analogy and Identity

The Online Merriam Webster Dictionary (as of 20 July 2014) provides a starting place for considering cross-species comparisons, with particular regard to the related notions of homology and analogy. This source’s first three considerations of homology include the following. “1) a similarity often attributable to common origin; 2) a. likeness in structure between parts of different organisms (as the wing of a bat and the human arm) due to evolutionary differentiation from a corresponding part in a common ancestor; b. correspondence in structure between a series of parts (as vertebrae) in the same individual; 3) similarity of nucleotide or amino acid sequence (as in nucleic acids or proteins).” The four considerations of analogy were the following. “1) the inference that, if two or more things agree with one another in some respects, they will probably agree in others; 2) a. the resemblance in some particulars between things otherwise unlike; b. the comparison based on such resemblance; 3) the correspondence between the members of pairs or sets of linguistic forms that serves as a basis for the creation of another form; 4) the correspondence in function between anatomical parts of different structure and origin.”

Our current approaches to understanding NF1 syndromes in general and NF1 neurofibromas specifically derives in large part from multiple, sometimes distantly related species. The most frequently used non-human metazoan organisms include Drosophila melanogaster, [21-30] Fugu rubripes, [31-33] zebrafish (Danio rerio),[34-38] Bicolor damselfish, [39-59] Mus musculus, [60-83]. Several species of the genus, Rattus, [84- 91] Bos primigenius taurus (Holstein cattle, etc.) [92-100] and chickens [101-105]. Given this heterogeneity of insects, teleosts, bovines, fowl and murines, we should be especially mindful as to whether the anatomic structures (and mutation-based lesions) are related to each other as “identical,” homologies or analogies [106-108]. For example, the wings of Drosophila and of bats are analogous, while the limbs of mice and humans are homologous. What about the nerves and ganglia of Drosophila? Are they “identical” to those of humans; or homologous or analogous? The lack of Schwann cells in Drosophila nerves, as well as these nerves’ distinctive patterns of formation, suggests that Drosophila and human nerves are more likely analogous than homologous. On the one hand, there is the lack of neurofibromas in D. melanogaster nf1 mutants [30,109]. On the other hand, a nerve overgrowth lesion “similar” to that seen in human NF1 is a result of egghead mutations (egh-/-) [30,109]. These two facts are critically relevant to elucidation of the praxitype. The overlap of the species-specific mutant phenotypes is more likely explained by the similarity of praxitypes than by the similarity of genotypes. In any event, this approach to comparative pathogenesis [106,108,110] has not heretofore been appropriately taken into account in exploring the origins and treatment strategies for the human NF1 syndrome and its individual lesions.

Genes/DNA and proteins on the one hand, and anatomic structures, including cell types, such as mast cells [111] and Schwann cells, [30,112-114] on the other hand, are often different from one species to another. Excessively casual use of the notion of homology in comparing the male prostate to the female counterpart, the urethrovaginal glands [115-125] represents another concrete example of the need for more perspicacity in such comparisons. Moreover, comparing multifaceted homologous structures leads to consideration of a unique type of gene, the supergene, [17-19,114,126] which type I propose is especially relevant to the NF1 locus. That is, complex phenotypes, whether wildtype or mutant, are more likely to involve complex genetic organization, either on the basis of syntenic gene clusters resistant to recombination [18,19,127-130] or supergene Mendelian loci sensu strictu [19;131-133]. Again, a key consequence of this treatise is the utilitarian proposal that the very large and complex NF1 gene is a supergene critical to the evolution of Homo sapiens in terms of the species’ distinctive, definitive elements. Intrinsic to these considerations is the need to focus both on the function of NF1 wildtype alleles (especially in terms of praxitypes and phenotypes) and on a more perspicacious sorting out of the NF1 syndrome phenotypes in terms of distinguishing its elements as either features, consequences or complications [13].

This homology interlude especially emphasizes the need to be more expansive – and simultaneously more precise – in our characterization of phenotypes: both for inter-species comparisons and for acknowledging that the DNA alphabetic sequence is only part of the genetic story. We also need to know the details of how the DNA yields the phenotypes being compared. While the DNA sequences account for the similarities, it is the praxitypes that account for the differences.

The Praxitype and Contagion

Above, I proposed a model of the paired genotype (γ) and phenotype (φ), which, for completeness, requires the praxitype (π). For further clarification, I suggest a comparison with the established canonical model of the paired infectious agent, or IA (virus, microbe, parasite), and associated epidemic disease, or ED (clinical syndrome), combined with the epidemiological control element, contagion (CT). Modalities relevant to the practices and control of contagion include administrative actions such as swamp drainage, DDT spraying and so on. These administrative actions are directed at the contagion parameters, not simply at the culprit organism. The focus is on the operational elements – the “practices” – of selected IA populations [134]. In order to control – to some realistic degree – infectious diseases characterized, if not defined, by human epidemics, solely detailing individual organisms (e.g., Vibrio cholera) does not afford a way to control the epidemics. Rather, it is the details about how a population of IAs interact with – engage in a practice with – populations of humans (and usually other organisms as well). Parenthetically, understanding “swarming” typical of certain organisms is not decipherable from even the most detailed analysis of an individual organism within a species. The behavior of the population of individuals during the swarming activity must be the target for investigation and elucidation of swarming [135-137].

For genetic disorders or, more generally, their phenotypes, as with epidemic infectious diseases (plagues), one must go beyond the individual organisms (or, sometimes, simply their different cell types) to consideration of public health principles and such. Understanding genetics and overcoming genetic disease is impossible without recognizing and influencing the praxitype, the phenomena or practices connecting genotype with phenotype, γ with φ. I suggest that the notion of contagion is comparable to the notion of praxitype in understanding critical elements of the relationship of genotype to phenotype. We have gone from (IA → ED) to (IA →CT → ED) for epidemic infectious diseases and now must go from (γ → φ) to (γ → π → φ) for genetics and genetic disorders.

1. Lou XY. UGMDR: a unified conceptual framework for detection of multifactor interactions underlying complex traits. Heredity (Edinb). 2015; 114: 255-261.

2. Chen X, Wang L. Integrating biological knowledge with gene expression profiles for survival prediction of cancer. J Comput Biol. 2009; 16: 265-278.

3. Riccardi VM: Neurofibromatosis: Phenotype, Natural History and Pathogenesis. ed 2, Baltimore, Johns Hopkins University Press. 1992.

4. Riccardi VM: von Recklinghausen Disease: 130 Years; in Upadhyaya M, Cooper DN, (eds): Neurofibromatosis Type 1: Molecular and Cellular Biology. Heidelberg. 2012; pp 1-15.

5. Ferner RE, Huson SM: Management and treatment of “Complex Neurofibromatosis 1”; in Upadhyaya M, Cooper DN, (eds): Neurofibromatosis Type 1: Molecular and Cellular Biology. Heidelberg. 2012; 31-45.

6. Upadhyaya M, Cooper DN (editors): Neurofibromatosis Type 1: Molecular and Cellular Biology: Heidelberg, Springer, 2012.

7. Brunskill EW, Potter SS. RNA-Seq defines novel genes, RNA processing patterns and enhancer maps for the early stages of nephrogenesis: Hox supergenes. Dev Biol. 2012; 368: 4-17.

8. Larizza L, Gervasini C, Natacci F, Riva P. Developmental abnormalities and cancer predisposition in neurofibromatosis type 1. Curr Mol Med. 2009; 9: 634-653.

9. Scheffzek K, Welti S: Neurofibromin: Protein domains and functional characteristics; in Upadhyaya M, Cooper DN, (eds): Neurofibromatosis Type 1: Molecular and Cellular Biology. 2012; 305-326.

10. Messiaen LM, Callens T, Mortier G, Beysen D, Vandenbroucke I, Van Roy N, et al. Exhaustive mutation analysis of the NF1 gene allows identification of 95% of mutations and reveals a high frequency of unusual splicing defects. Hum Mutat. 2000; 15: 541-555.

11. Wimmer K, Yao S, Claes K, Kehrer-Sawatzki H, Tinschert S, De Raedt T, et al. Spectrum of single- and multiexon NF1 copy number changes in a cohort of 1,100 unselected NF1 patients. Genes Chromosomes Cancer. 2006; 45: 265-276.

12. Ko JM, Sohn YB, Jeong SY, Kim HJ, Messiaen LM. Mutation spectrum of NF1 and clinical characteristics in 78 Korean patients with neurofibromatosis type 1. Pediatr Neurol. 2013; 48: 447-453.

13. Riccardi VM. Neurofibromatosis type 1 is a disorder of dysplasia: the importance of distinguishing features, consequences, and complications. Birth Defects Res A Clin Mol Teratol. 2010; 88: 9-14.

14. Kunte K, Zhang W, Tenger-Trolander A, Palmer DH, Martin A, Reed RD, et al. Double sex is a mimicry supergene. Nature. 2014; 507: 229-232.

15. Calvo-Dmgz D, Gálvez JF, Glez-Peña D, Gómez-Meire S, Fdez-Riverola F. Using variable precision rough set for selection and classification of biological knowledge integrated in DNA gene expression. J Integr Bioinform. 2012; 9: 199.

16. Jones RT, Salazar PA, Ffrench-Constant RH, Jiggins CD, Joron M. Evolution of a mimicry supergene from a multilocus architecture. Proc Biol Sci. 2012; 279: 316-325.

17. Thompson MJ, Jiggins CD. Supergenes and their role in evolution. Heredity (Edinb). 2014; 113: 1-8.

18. Schwander T, Libbrecht R, Keller L. Supergenes and complex phenotypes. Curr Biol. 2014; 24: R288-294.

19. Wagner GP: Homology, Genes and Evolutionary Innovation. Princeton, NJ, Princeton University Press. 2014.

20. Therman E, Laxova R, Susman B. The critical region on the human Xq. Hum Genet. 1990; 85: 455-461.

21. Hackstein JH. The lethal prune/Killer-of-prune interaction of Drosophila causes a syndrome resembling human neurofibromatosis (NF1). Eur J Cell Biol. 1992; 58: 429-444.

22. Williams JA, Su HS, Bernards A, Field J, Sehgal A. A circadian output in Drosophila mediated by neurofibromatosis-1 and Ras/MAPK. Science. 2001; 293: 2251-2256.

23. The I, Hannigan GE, Cowley GS, Reginald S, Zhong Y, Gusella JF, et al. Rescue of a Drosophila NF1 mutant phenotype by protein kinase A. Science. 1997; 276: 791-794.

24. Walker JA, Tchoudakova AV, McKenney PT, Brill S, Wu D, Cowley GS, et al. Reduced growth of Drosophila neurofibromatosis 1 mutants reflects a non-cell-autonomous requirement for GTPase-Activating Protein activity in larval neurons. Genes Dev. 2006; 20: 3311-3323.

25. Tong JJ, Schriner SE, McCleary D, Day BJ, Wallace DC. Life extension through neurofibromin mitochondrial regulation and antioxidant therapy for neurofibromatosis-1 in Drosophila melanogaster. Nat Genet. 2007; 39: 476-485.

26. Guo HF, Tong J, Hannan F, Luo L, Zhong Y. A neurofibromatosis-1- regulated pathway is required for learning in Drosophila. Nature. 2000; 403: 895-898.

27. Gouzi JY, Moressis A, Walker JA, Apostolopoulou AA, Palmer RH, Bernards A, et al. The receptor tyrosine kinase Alk controls neurofibromin functions in Drosophila growth and learning. PLoS Genet. 2011; 7: e1002281.

28. Tsai PI, Wang M, Kao HH, Cheng YJ, Walker JA, Chen RH, et al. Neurofibromin mediates FAK signaling in confining synapse growth at Drosophila neuromuscular junctions. J Neurosci. 2012; 32: 16971- 16981.

29. Lee SF, Eyre-Walker YC, Rane RV, Reuter C, Vinti G, Rako L, et al. Polymorphism in the neurofibromin gene, Nf1, is associated with antagonistic selection on wing size and development time in Drosophila melanogaster. Mol Ecol. 2013; 22: 2716-2725.

30. Dahlgaard K, Jung A, Qvortrup K, Clausen H, Kjaerulff O, Wandall HH. Neurofibromatosis-like phenotype in Drosophila caused by lack of glucosylceramide extension. Proc Natl Acad Sci U S A. 2012; 109: 6987-6992.

31. Kehrer-Sawatzki H, Maier C, Moschgath E, Elgar G, Krone W. Characterization of three genes, AKAP84, BAW and WSB1, located 3’ to the neurofibromatosis type 1 locus in Fugu rubripes. Gene. 1999; 235: 1-11.

32. Kehrer-Sawatzki H, Maier C, Moschgath E, Elgar G, Krone W. Genomic characterization of the Neurofibromatosis Type 1 gene of Fugu rubripes. Gene. 1998; 222: 145-153.

33. Vourc’h P, Andres C. Oligodendrocyte myelin glycoprotein (OMgp): evolution, structure and function. Brain Res Brain Res Rev. 2004; 45: 115-124.

34. Germanà A, Paruta S, Germanà GP, Ochoa-Erena FJ, Montalbano G, Cobo J, et al. Differential distribution of S100 protein and calretinin in mechanosensory and chemosensory cells of adult zebrafish (Danio rerio). Brain Res. 2007; 1162: 48-55.

35. Padmanabhan A, Lee JS, Ismat FA, Lu MM, Lawson ND, Kanki JP, et al. Cardiac and vascular functions of the zebrafish orthologues of the type I neurofibromatosis gene NFI. Proc Natl Acad Sci U S A. 2009; 106: 22305-22310.

36. Feitsma H, Kuiper RV, Korving J, Nijman IJ, Cuppen E. Zebrafish with mutations in mismatch repair genes develop neurofibromas and other tumors. Cancer Res. 2008; 68: 5059-5066.

37. Shin J, Padmanabhan A, De Groh ED, Lee JS, Haidar S, Dahlberg S, et al. Zebrafish neurofibromatosis type 1 genes have redundant functions in tumorigenesis and embryonic development. Dis Model Mech. 2012; 5: 881-894.

38. Lee JS, Padmanabhan A, Shin J, Zhu S, Guo F, Kanki JP, et al. Oligodendrocyte progenitor cell numbers and migration are regulated by the zebrafish orthologs of the NF1 tumor suppressor gene. Hum Mol Genet. 2010; 19: 4643-4653.

39. Schmale MC, Hensley GT. Transmissibility of a neurofibromatosis-like disease in bicolor damselfish. Cancer Res. 1988; 48: 3828-3833.

40. Schmale MC, Hensley G, Udey LR. Neurofibromatosis, von Recklinghausen’s disease, multiple schwannomas, malignant schwannomas. Multiple schwannomas in the bicolor damselfish, Pomacentrus partitus (pisces, pomacentridae). Am J Pathol. 1983; 112: 238-241.

41. Schmale MC, Hensley G, Udey LR. Neurofibromatosis, von Recklinghausen’s disease, multiple schwannomas, malignant schwannomas. Multiple schwannomas in the bicolor damselfish, Pomacentrus partitus (pisces, pomacentridae). Am J Pathol. 1983; 112: 238-241.

42. Schmale MC, Hensley GT, Udey LR. Neurofibromatosis in the bicolor damselfish (Pomacentrus partitus) as a model of von Recklinghausen neurofibromatosis. Ann N Y Acad Sci. 1986; 486: 386-402.

43. Schmale MC, Udey LR, Riccardi VM: Bicolor damselfish neurofibromatosis (NF): A model for human NF. Am J Hum Genet 1984; 36(Supplement):A36-A36.

44. Riccardi VM, Schmale MC: Neurofibromatosis (NF) in the bicolor damselfish (BDF); Am J Hum Genet 1986; 39(Supplement):A39-A39.

45. Lacson JM, Riccardi VM, Morizot DC: Possible genetic etiology of damselfish neurofibromatosis (DNF): Generic differentiation of bicolor damselfish (Pomacentrus partitus) populations. Neurofibromatosis 1988; 1: 253-259.

46. Lacson JM, Riccardi VM, Calhoun SW, Morizot DC. Hurricanes and genetic drift in populations of bicolor damselfish. Marine Biol 1989; 103: 445-451.

47. Fieber LA, Schmale MC: Potassium currents from healthy and neurofibroma-derived Schwann cells in the bicolor damselfish, a model of human neurofibromatosis; Soc Neurosci Abstracts 1992; 18:1491-1491.

48. McKinney EC, Schmale MC. Immune dysfunction in experimental versus naturally occurring neurofibromatosis in damselfish. Anticancer Res. 1994; 14: 201-204.

49. Fieber LA, Schmale MC. Differences in a K current in Schwann cells from normal and neurofibromatosis-infected damselfish. Glia. 1994; 11: 64-72.

50. Vicha DL, Schmale MC. Morphology and distribution of eosinophilic granulocytes in damselfish neurofibromatosis, a model of mast cell distribution in neurofibromatosis type 1. Anticancer Res. 1994; 14: 947-952.

51. Schmale MC, Gill KA, Cacal SM, Baribeau SD. Characterization of Schwann cells from normal nerves and from neurofibromas in the bicolour damselfish. J Neurocytol. 1994; 23: 668-681.

52. Schmale MC, Gibbs PD, Campbell CE. A virus-like agent associated with neurofibromatosis in damselfish. Dis Aquat Organ. 2002; 49: 107-115.

53. Campbell CE, Gibbs PD, Schmale MC. Progression of infection and tumor development in damselfish. Mar Biotechnol (NY). 2001; 3: S107-114.

54. Rahn JJ, Gibbs PD, Schmale MC. Patterns of transcription of a virus like agent in tumor and non-tumor tissues in bicolor damselfish. Comp Biochem Physiol C Toxicol Pharmacol. 2004; 138: 401-409.

55. Schmale MC, Vicha D, Cacal SM. Degranulation of eosinophilic granule cells in neurofibromas and gastrointestinal tract in the bicolor damselfish. Fish Shellfish Immunol. 2004; 17: 53-63.

56. Schmale MC, Gibbs PD, Campbell CE. A virus-like agent associated with neurofibromatosis in damselfish. Dis Aquat Organ. 2002; 49: 107-115.

57. Schmale MC, Aman MR, Gill KA. A retrovirus isolated from cell lines derived from neurofibromas in bicolor damselfish (Pomacentrus partitus). J Gen Virol. 1996; 77: 1181-1187.

58. Preker P, Nielsen J, Kammler S, Lykke-Andersen S, Christensen MS, Mapendano CK, et al. RNA exosome depletion reveals transcription upstream of active human promoters. Science. 2008; 322: 1851-1854.

59. Xu Y, Chiamvimonvat N, Vázquez AE, Akunuru S, Ratner N, Yamoah EN. Gene-targeted deletion of neurofibromin enhances the expression of a transient outward K+ current in Schwann cells: a protein kinase A-mediated mechanism. J Neurosci. 2002; 22: 9194-9202.

60. Hinrichs SH, Nerenberg M, Reynolds RK, Khoury G, Jay G. A transgenic mouse model for human neurofibromatosis. Science. 1987; 237: 1340-1343.

61. Nerenberg MI, Minor T, Nagashima K, Takebayashi K, Akai K, Wiley CA, et al. Absence of association of HTLV-I infection with type 1 neurofibromatosis in the United States or Japan. Neurology. 1991; 41: 1687-1689.

62. Rubin JB1, Gutmann DH. Neurofibromatosis type 1 - a model for nervous system tumour formation? Nat Rev Cancer. 2005; 5: 557-564.

63. Kuorilehto T1, Nissinen M, Koivunen J, Benson MD, Peltonen J. NF1 tumor suppressor protein and mRNA in skeletal tissues of developing and adult normal mouse and NF1-deficient embryos. J Bone Miner Res. 2004; 19: 983-989.

64. Stemmer-Rachamimov AO1, Louis DN, Nielsen GP, Antonescu CR, Borowsky AD, Bronson RT, Burns DK. Comparative pathology of nerve sheath tumors in mouse models and humans. Cancer Res. 2004; 64: 3718-3724.

65. Lush ME1, Li Y, Kwon CH, Chen J, Parada LF. Neurofibromin is required for barrel formation in the mouse somatosensory cortex. J Neurosci. 2008; 28: 1580-1587.

66. Lasater EA1, Bessler WK, Mead LE, Horn WE, Clapp DW, Conway SJ, Ingram DA. Nf1+/- mice have increased neointima formation via hyperactivation of a Gleevec sensitive molecular pathway. Hum Mol Genet. 2008; 17: 2336-2344.

67. Costa RM1, Federov NB, Kogan JH, Murphy GG, Stern J, Ohno M, Kucherlapati R. Mechanism for the learning deficits in a mouse model of neurofibromatosis type 1. Nature. 2002; 415: 526-530.

68. Kim HA1, Ling B, Ratner N. Nf1-deficient mouse Schwann cells are angiogenic and invasive and can be induced to hyperproliferate: reversion of some phenotypes by an inhibitor of farnesyl protein transferase. Mol Cell Biol. 1997; 17: 862-872.

69. Powers JF1, Evinger MJ, Zhi J, Picard KL, Tischler AS. Pheochromocytomas in Nf1 knockout mice express a neural progenitor gene expression profile. Neuroscience. 2007; 147: 928- 937.

70. Wiesner SM, Geurts JL, Diers MD, Bergerson RJ, Hasz DE, Morgan KJ, et al. Nf1 mutant mice with p19ARF gene loss develop accelerated hematopoietic disease resembling acute leukemia with a variable phenotype. Am J Hematol. 2011; 86: 579-585.

71. Duan JH, Wang Y, Duarte D, Vasko MR, Nicol GD, Hingtgen CM. Ras signaling pathways mediate NGF-induced enhancement of excitability of small-diameter capsaicin-sensitive sensory neurons from wildtype but not Nf1+/- mice. Neurosci Lett. 2011; 496: 70-74.

72. Castorina A, Leggio GM, Giunta S, Magro G, Scapagnini G, Drago F, et al. Neurofibromin and amyloid precursor protein expression in dopamine D3 receptor knock-out mice brains. Neurochem Res. 2011; 36: 426-434.

73. Garza R, Hudson RA 3rd, McMahan CA, Walter CA, Vogel KS. A mild mutator phenotype arises in a mouse model for malignancies associated with neurofibromatosis type 1. Mutat Res. 2007; 615: 98- 110.

74. Robinson A, Kloog Y, Stein R, Assaf Y. Motor deficits and neurofibromatosis type 1 (NF1)-associated MRI impairments in a mouse model of NF1. NMR Biomed. 2010; 23: 1173-1180.

75. Perrin GQ, Fishbein L, Thomson SA, Thomas SL, Stephens K, Garbern JY, et al. Plexiform-like neurofibromas develop in the mouse by intraneural xenograft of an NF1 tumor-derived Schwann cell line. J Neurosci Res. 2007; 85: 1347-1357.

76. El-Hoss J, Sullivan K, Cheng T, Yu NY, Bobyn JD, Peacock L, et al. A murine model of neurofibromatosis type 1 tibial pseudarthrosis featuring proliferative fibrous tissue and osteoclast-like cells. J Bone Miner Res. 2012; 27: 68-78.

77. Kazmi SJ, Byer SJ, Eckert JM, Turk AN, Huijbregts RP, Brossier NM, et al.: Transgenic Mice Overexpressing Neuregulin-1 Model Neurofibroma Malignant Peripheral Nerve Sheath Tumor Progression and Implicate Specific Chromosomal Copy Number Variations in Tumorigenesis. Am J Pathol 2013; 182: 646-667.

78. Venturin M, Bentivegna A, Moroni R, Larizza L, Riva P. Evidence by expression analysis of candidate genes for congenital heart defects in the NF1 microdeletion interval. Ann Hum Genet. 2005; 69: 508-516.

79. Simmons GW, Pong WW, Emnett RJ, White CR, Gianino SM, Rodriguez FJ, et al. Neurofibromatosis-1 heterozygosity increases microglia in a spatially and temporally restricted pattern relevant to mouse optic glioma formation and growth. J Neuropathol Exp Neurol. 2011; 70: 51-62.

80. O’Brien DE, Brenner DS, Gutmann DH, Gereau RW 4th. Assessment of pain and itch behavior in a mouse model of neurofibromatosis type 1. J Pain. 2013; 14: 628-637.

81. Diggs-Andrews KA, Brown JA, Gianino SM, Rubin JB, Wozniak DF, Gutmann DH. Sex Is a major determinant of neuronal dysfunction in neurofibromatosis type 1. Ann Neurol. 2014; 75: 309-316.

82. Lin L, Chen J, Richardson JA, Parada LF. Mice lacking neurofibromin develop gastric hyperplasia. Am J Physiol Gastrointest Liver Physiol. 2009; 297: G751-761.

83. De la Croix NJ, Makowski AJ, Uppuganti S, Vignaux G, Ono K, Perrien DS, et al. Asfotase-alpha improves bone growth, mineralization and strength in mouse models of neurofibromatosis type-1. Nat Med 2014; 20: 904-910.

84. Daston MM, Scrable H, Nordlund M, Sturbaum AK, Nissen LM, Ratner N. The protein product of the neurofibromatosis type 1 gene is expressed at highest abundance in neurons, Schwann cells, and oligodendrocytes. Neuron. 1992; 8: 415-428.

85. Urban BA, Fishman EK, Hruban RH, Cameron JL. CT findings in cystic schwannoma of the pancreas. J Comput Assist Tomogr. 1992; 16: 492- 493.

86. Malhotra R, Ratner N. Localization of neurofibromin to keratinocytes and melanocytes in developing rat and human skin. J Invest Dermatol. 1994; 102: 812-818.

87. Kuorilehto T, Ekholm E, Nissinen M, Hietaniemi K, Hiltunen A, Paavolainen P, et al. NF1 gene expression in mouse fracture healing and in experimental rat pseudarthrosis. J Histochem Cytochem. 2006; 54: 363-370.

88. Lee TK, Friedman JM. Analysis of NF1 transcriptional regulatory elements. Am J Med Genet A. 2005; 137: 130-135.

89. Barron VA, Zhu H, Hinman MN, Ladd AN, Lou H. The neurofibromatosis type I pre-mRNA is a novel target of CELF protein-mediated splicing regulation. Nucleic Acids Res. 2010; 38: 253-264.

90. Baron P1, Kreider B. Axons induce differentiation of neurofibroma Schwann-like cells. Acta Neuropathol. 1991; 81: 491-495.

91. Norton KK, Xu J, Gutmann DH. Expression of the neurofibromatosis I gene product, neurofibromin, in blood vessel endothelial cells and smooth muscle. Neurobiol Dis. 1995; 2: 13-21.

92. Cibis GW, Whittaker CK, Wood WE. Intraocular extension of optic nerve meningioma in a case of neurofibromatosis. Arch Ophthalmol. 1985; 103: 404-406.

93. Doughty FR. Incidence of neurofibroma in cattle in abattoirs in New South Wales. Aust Vet J. 1977; 53: 280-281.

94. Johnson RC, Anderson WI, Luther PB, Ryan AM. Multicentric schwannoma in a mature Holstein cow. Vet Rec. 1988; 123: 649-650.

95. Sartin EA, Doran SE, Riddell MG, Herrera GA, Tennyson GS, D’Andrea G, et al. Characterization of naturally occurring cutaneous neurofibromatosis in Holstein cattle. A disorder resembling neurofibromatosis type 1 in humans. Am J Pathol. 1994; 145: 1168- 1174.

96. Canfield P. The ultrastructure of bovine peripheral nerve sheath tumours. Vet Pathol. 1978; 15: 292-300.

97. Omi K, Kitano Y, Agawa H, Kadota K. An immunohistochemical study of peripheral neuroblastoma, ganglioneuroblastoma, anaplastic ganglioglioma, schwannoma and neurofibroma in cattle. J Comp Pathol. 1994; 111: 1-14.

98. Nielsen AB, Jensen HE, Leifsson PS. Immunohistochemistry for 2’,3’-cyclic nucleotide-3’-phosphohydrolase in 63 bovine peripheral nerve sheath tumors. Vet Pathol. 2011; 48: 796-802.

99. Geldermann H, He H, Bobal P, Bartenschlager H, Preuss S. Comparison of DNA variants in the PRNP and NF1 regions between bovine spongiform encephalopathy and control cattle. Anim Genet. 2006; 37: 469-474.

100. Stöber M, Geburek F, Liebler-Tenorio EM, Sohrt J, Wohlsein P. Nerve sheath tumors in cattle: literature review and case report. Dtsch Tierarztl Wochenschr. 2001; 108: 269-272.

101. Ciment G. Cloning of the chicken homolog of the NF-1 gene product and its expression during early chicken embryogenesis. National NF Foundation Consortium Program.1992; 16.

102. Schafer GL, Ciment G, Stocker KM, Baizer L. Analysis of the sequence and embryonic expression of chicken neurofibromin mRNA. Mol Chem Neuropathol. 1993; 18: 267-278.

103. Baizer L, Ciment G, Hendrickson SK, Schafer GL. Regulated expression of the neurofibromin type I transcript in the developing chicken brain. J Neurochem. 1993; 61: 2054-2060.

104. Bhattacharyya A, Oppenheim RW, Prevette D, Moore BW, Brackenbury R, Ratner N,. S100 is present in developing chicken neurons and Schwann cells and promotes motor neuron survival in vivo. J Neurobiol. 1992; 23: 451-466.

105. Schöniger S, Summers BA. Localized, plexiform, diffuse, and other variants of neurofibroma in 12 dogs, 2 horses, and a chicken. Vet Pathol. 2009; 46: 904-915.

106. Bejerano G, Pheasant M, Makunin I, Stephen S, Kent WJ, Mattick JS, Haussler D. Ultraconserved elements in the human genome. Science. 2004; 304: 1321-1325.

107. Gallant JR, Traeger LL2, Volkening JD3, Moffett H4, Chen PH5, Novina CD5, Phillips GN Jr6. Nonhuman genetics. Genomic basis for the convergent evolution of electric organs. Science. 2014; 344: 1522-1525.

108. Artieri CG, Singh RS. Demystifying phenotypes: The comparative genomics of evo-devo. Fly (Austin). 2010; 4: 18-20.

109. Goode S, Melnick M, Chou TB, Perrimon N: The neurogenic genes egghead and brainiac define a novel signaling pathway essential for epithelial morphogenesis during Drosophila oogenesis. Development 1996;122: 3863-3879.

110. Bar-Peled L, Chantranupong L, Cherniack AD, Chen WW, Ottina KA, Grabiner BC, Spear ED. A Tumor suppressor complex with GAP activity for the Rag GTPases that signal amino acid sufficiency to mTORC1. Science. 2013; 340: 1100-1106.

111. Blennerhassett MG, Tomioka M, Bienenstock J. Formation of contacts between mast cells and sympathetic neurons in vitro. Cell Tissue Res. 1991; 265: 121-128.

112. Banerjee S, Bhat MA. Glial ensheathment of peripheral axons in Drosophila. J Neurosci Res. 2008; 86: 1189-1198.

113. Holland LZ, Carvalho JE, Escriva H, Laudet V, Schubert M, Shimeld SM, Yu JK. Evolution of bilaterian central nervous systems: a single origin? Evodevo. 2013; 4: 27.

114. von Hilchen CM, Bustos AE, Giangrande A, Technau GM, Altenhein B. Predetermined embryonic glial cells form the distinct glial sheaths of the Drosophila peripheral nervous system. Development. 2013; 140: 3657-3668.

115. HUFFMAN JW. The detailed anatomy of the para-urethral ducts in the adult human female. Am J Obstet Gynecol. 1948; 55: 86-101.

116. Heath D. Female ejaculation: its relationship to disturbances of erotic function. Med Hypotheses. 1987; 24: 103-106.

117. Satoh H, Mori K, Furuhama K. Morphological and immunohistochemical characteristics of the heterogeneous prostate-like glands (paraurethral gland) seen in female Brown Norway rats. Toxicol Pathol. 2001; 29: 237-241.

118. Tepper SL, Jagirdar J, Heath D, Geller SA: Homology between the female paraurethral (Skene’s) glands and the prostate. Immunohistochemical demonstration. Arch Pathol Lab Med. 1984; 108: 423-425.

119. Korenchevsky V. The female prostatic gland and its reaction to male sexual compounds. J Physiol. 1937; 90: 371-376.

120. Brambell FW, Davis DH. The normal occurrence, structure and homology of prostate glands in adult female Mastomys erythroleucus Temm. J Anat. 1940; 75: 64-74.

121. Smith AF, Landon GV, Ghanadian R, Chisholm GD. The ultrastructure of the male and female prostate of Praomys (Mastomys) natalensis. I. Normal, castrated and ovariectomised animals. Cell Tissue Res. 1978; 190: 539-552.

122. Johnson FP. The homologue of the prostate in the female. J Urol. 1922; 8: 13-27.

123. LINTGEN C, HERBUT PA. A clinico-pathological study of 100 female urethras. J Urol. 1946; 55: 298-305.

124. Thielen JL, Volzing KG, Collier LS, Green LE, Largaespada DA, Marker PC: Markers of prostate region-specific epithelial identity define anatomical locations in the mouse prostate that are molecularly similar to human prostate cancers. Differentiation. 2007; 75: 49-61.

125. Zaviacic M. The adult human female prostata homologue and the male prostate gland: a comparative enzyme-histochemical study. Acta Histochem. 1985; 77: 19-31.

126. Norris HW: Branchial nerve homologies. Z Morphol Anthropol 1924; 24: 211-226.

127. Jenne DE, Tinschert S, Reimann H, Lasinger W, Thiel G, Hameister H, Kehrer-Sawatzki H. Molecular characterization and gene content of breakpoint boundaries in patients with neurofibromatosis type 1 with 17q11.2 microdeletions. Am J Hum Genet. 2001; 69: 516-527.

128. Roehl AC1, Vogt J, Mussotter T, Zickler AN, Spöti H, Högel J, Chuzhanova NA. Intrachromosomal mitotic nonallelic homologous recombination is the major molecular mechanism underlying type-2 NF1 deletions. Hum Mutat. 2010; 31: 1163-1173.

129. Kong A, Gudbjartsson DF, Sainz J, Jonsdottir GM, Gudjonsson SA, Richardsson B, Sigurdardottir S. A high-resolution recombination map of the human genome. Nat Genet. 2002; 31: 241-247.

130. Lupski JR. 2002 Curt Stern Award Address. Genomic disorders recombination-based disease resulting from genomic architecture. Am J Hum Genet. 2003; 72: 246-252.

131. Chakravarti A, Kapoor A. Genetics. Mendelian puzzles. Science. 2012; 335: 930-931.

132. Tabor HK, Auer PL, Jamal SM, Chong JX, Yu JH, Gordon AS, et.al. Pathogenic variants for Mendelian and complex traits in exomes of 6,517 European and African Americans: implications for the return of incidental results. Am J Hum Genet. 2014; 95: 183-193.

133. Fenger M: Next generation genetics. Frontiers in Genetics. 2014; 5: 322 .

134. McNeill WH: Plagues and People. New York, Anchor Books. 1976.

135. Kerr RA. Ocean science. Creatures great and small are stirring the ocean. Science. 2006; 313: 1717.

136. Joanny JF, Ramaswamy S. Biological physics: Filaments band together. Nature. 2010; 467: 33-34.

137. Luiggi C. Crowd control. The Scientist 2013; 27: 26-33.