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.

Variation in male reproductive system characters in Corydoradinae (Loricarioidei: Callichthyidae) reflects the occurrence of different lineages in this subfamily

“…Anatomical and histological data obtained in this study reveal that species of Corydoradinae analyzed share, independently of the lineages they belong, the typical testicular structure observed in fishes and shared by other vertebrates (Grier et al, 2016), consisting in the division on germinal and interstitial compartments (Koulish et al, 2002;Quagio-Grassiotto et al, 2013;Grier et al, 2016).…”

Morpho‐Functional Features of the Gonads ofDanio rerio: the Role of Brain‐Derived Neurotrophic Factor

“…Gametogenesis in vertebrates is regulated by a close interplay of cells, hormones, and growth factors (Grier et al, 2016). Particularly in mammals, neurotrophins, which include nerve growth factor, brain derived neurotrophic factor, neurotrophin 3, and neurotrophin 4/5, are growth factors playing key roles either in folliculogenesis (Streiter et al, 2016) or spermatogenesis (Li and Zhou, 2013).…”

Testicular structure and spermatogenesis of the oviparous goodeids Crenichthys baileyi (Gilbert, 1893) and Empetrichthys latos Miller, 1948 (Teleostei, Cyprinodontiformes)

“…Histological examination of the testes of C. baileyi and E. latos confirms that they are composed of germinal and interstitial compartments. Both compartments are always separated by a basement membrane in all vertebrates (Grier et al, ). The germinal compartment is composed of the germinal epithelium formed by two cell types: somatic Sertoli cells and germ cells.…”

“…Archival museum specimens have proven to be a rich source of data for studies of comparative gonad morphology (e.g., Grier & Parenti, ; Grier, Uribe, Lo Nostro, Mims, & Parenti, ; Parenti & Grier, ; Parenti, Grier, & Uribe, ). For many vertebrate taxa, especially rare, endangered, or extinct species, historical museum specimens may be the only study material available.…”