title: Conserved form and function of the germinal epithelium through 500 million years of vertebrate evolution.
abstract: The germinal epithelium, i.e., the site of germ cell production in males and females, has maintained a constant form and function throughout 500 million years of vertebrate evolution. The distinguishing characteristic of germinal epithelia among all vertebrates, males, and females, is the presence of germ cells among somatic epithelial cells. The somatic epithelial cells, Sertoli cells in males or follicle (granulosa) cells in females, encompass and isolate germ cells. Morphology of all vertebrate germinal epithelia conforms to the standard definition of an epithelium: epithelial cells are interconnected, border a body surface or lumen, are avascular and are supported by a basement membrane. Variation in morphology of gonads, which develop from the germinal epithelium, is correlated with the evolution of reproductive modes. In hagfishes, lampreys, and elasmobranchs, the germinal epithelia of males produce spermatocysts. A major rearrangement of testis morphology diagnoses osteichthyans: the spermatocysts are arranged in tubules or lobules. In protogynous (female to male) sex reversal in teleost fishes, female germinal epithelial cells (prefollicle cells) and oogonia transform into the first male somatic cells (Sertoli cells) and spermatogonia in the developing testis lobules. This common origin of cell types from the germinal epithelium in fishes with protogynous sex reversal supports the homology of Sertoli cells and follicle cells. Spermatogenesis in amphibians develops within spermatocysts in testis lobules. In amniotes vertebrates, the testis is composed of seminiferous tubules wherein spermatogenesis occurs radially. Emerging research indicates that some mammals do not have lifetime determinate fecundity. The fact emerged that germinal epithelia occur in the gonads of all vertebrates examined herein of both sexes and has the same form and function across all vertebrate taxa. Continued study of the form and function of the germinal epithelium in vertebrates will increasingly clarify our understanding of vertebrate reproduction. J. Morphol. 277:1014-1044, 2016. © 2016 Wiley Periodicals, Inc.
authors.affiliation: Fish and Wildlife Research Institute, St. Petersburg, Florida.|Department of Vertebrate Zoology, Division of Fishes, National Museum of Natural History, MRC 159, Smithsonian Institution, Washington, DC.
authors.forename: Harry J
authors.initials: HJ
authors.lastname: Grier
authors.affiliation: Laboratorio Biología de la Reproducción, Departamento de Biología Comparada, Facultad de Ciencias, Universidad Nacional Autónoma de México, Ciudad de México, 04510, México.
authors.forename: Mari Carmen
authors.initials: MC
authors.lastname: Uribe
authors.affiliation: Laboratorio de Ecotoxicología Acuática, Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires & Instituto de Biodiversidad y Biología Experimental y Aplicada, CONICET-UBA, C1428EGA Buenos Aires, Argentina.
authors.forename: Fabiana L
authors.initials: FL
authors.lastname: Lo Nostro
authors.affiliation: Aquaculture Research Center. Kentucky State University, Frankfort, KY, 40601.
authors.forename: Steven D
authors.initials: SD
authors.lastname: Mims
authors.affiliation: Department of Vertebrate Zoology, Division of Fishes, National Museum of Natural History, MRC 159, Smithsonian Institution, Washington, DC.
authors.forename: Lynne R
authors.initials: LR
authors.lastname: Parenti
mesh_terms: D000663:Amphibians / Q000502:physiology; D000818:Animals; D005075:Biological Evolution; D004848:Epithelium / Q000502:physiology*; D005260:Female; D005399:Fishes / Q000502:physiology; D008297:Male; D006080:Ovarian Follicle / Q000166:cytology*; D012104:Reptiles / Q000502:physiology; D012708:Sertoli Cells / Q000378:metabolism*; D013737:Testis / Q000166:cytology; D013997:Time Factors; D014714:Vertebrates / Q000502:physiology*
keywords: basement membrane; follicle complex; folliculogenesis; gametogenesis; gonads structure