Gonadal mRNA Expression Levels of TGFβ Superfamily Signaling Factors Correspond with Post-Hatching Morphological Development in American Alligators

Abstract

Paracrine factor signaling regulates many aspects of vertebrate gonadal development. We investigated key ovarian and testicular morphological markers of the American alligator (Alligator mississippiensis) during the first 5 months post-hatching and correlated gonadal development with mRNA expression levels of a suite of regulatory factors. In both sexes, we observed significant morphology changes, including ovarian follicle assembly and meiotic progression of testicular germ cells. Concomitant with these changes were sexually dimorphic and ontogenetically variable mRNA expressions. In ovaries, FOXL2, aromatase, and follistatin mRNA expression was greater than in testes at all ages. At one week after hatching, we observed ovarian medullary remodeling in association with elevated activin/inhibin βA subunit, follistatin, and aromatase mRNA expressions. Three and 5 months following hatching and concomitant with follicle assembly, ovaries showed increased mRNA expression levels of GDF9 and the mitotic factor PCNA. In testes, the activin/inhibin α and βB subunit transcript levels were greater than in ovaries at all ages. Elevated testicular expression of GDF9 mRNA levels at 5 months after hatching aligned with increased spermatogenic activity. We propose that the mRNA expression levels and concomitant morphological changes observed here affect the establishment of alligator reproductive health and later fertility.

Gonadal Differentiation in Reptiles Exhibiting Environmental Sex Determination

“…The mechanism underlying this pathology has been hypothesized as a disruption of the gonadotropin-estrogen-inhibin/activin signaling cascade [Guillette and Moore, 2006], but it is still poorly understood. Although further investigations on this signaling pathway have begun to elucidate the mechanisms of normal and abnormal folliculogenesis [Moore et al, 2010a[Moore et al, , c, d, 2012, reptilian folliculogenesis requires further study. This process could be one of the sensitive endpoints for investigations on the role of contaminant exposure early in life (see below).…”

Altered sex hormone concentrations and gonadal mRNA expression levels of activin signaling factors in hatchling alligators from a contaminated Florida lake

“…Follistatin is a TGF-β ligand antagonist that binds and neutralizes activins (Nakamura et al, '92; Welt et al, 2002). We have demonstrated the expression of Inhba, Inhbb, Fst , and Inha mRNA in alligator gonads during the first 5 months post-hatching (Moore et al, 2010a). Furthermore, expression levels were sexually dimorphic, with testes expressing elevated levels of Inha and Inhbb mRNA and ovaries expressing elevated Fst mRNA levels.…”

Loss of <i>R-Spondin1</i> and <i>Foxl2</i> Amplifies Female-to-Male Sex Reversal in XX Mice

“…Nevertheless, evidence is accumulating to suggest that FOXL2 is an important ovarian differentiating gene. Indeed, its ovarian-specific expression is conserved in all vertebrate species studied until now [Loffler et al, 2003;Baron et al, 2004;Govoroun et al, 2004;Wang et al, 2004;Nakamoto et al, 2006;Liu et al, 2007;Rhen et al, 2007;Wotton et al, 2007;Alam et al, 2008;Ijiri et al, 2008;Oshima et al, 2008;Siegfried and Nusslein-Volhard, 2008;Nakamoto et al, 2009;Okada et al, 2009;Shi et al, 2009;Amberg et al, 2010;Moore et al, 2010;Shoemaker-Daly et al, 2010;Wu et al, 2010], and in an invertebrate species such as the pacific oyster [Naimi et al, 2009]. In addition to the function of Foxl2 in development, Foxl2 is also required for ovarian homeostasis.…”