Developmental morphology of the neonatal alligator (Alligator mississippiensis) ovary

Abstract

American alligator (Alligator mississippiensis) ovary development is incomplete at hatching. During the months following hatching, the cortical processes of oogenesis started in ovo continues and folliculogenesis is initiated. Additionally, the medullary region of the gonad undergoes dramatic restructuring. We describe alligator ovarian histology at hatching, 1 week, 1 month, and 3 months of age in order to characterize the timing of morphological development and compare these findings to chicken ovary development. At hatching, the ovarian cortex presents a germinal epithelium containing oogonia and a few primary oocytes irregularly scattered between somatic epithelial cells. The hatchling medulla shows fragmentation indicative of the formation of lacunae. By 1 week of age, oocytes form growing nests and show increased interactions with somatic cells, indicative of the initiation of folliculogenesis. Medullary lacunae increase in diameter and contain secretory material in their lumen. At 1 month, nest sizes and lacunar diameters continue to enlarge. Pachytene oocytes surrounded by somatic cells are more frequent. Trabeculae composed of dense irregular connective tissue divide cortical nests. Three months after hatching oocytes in meiotic stages of prophase I up to diplotene are present. The ovary displays many enlarged follicles with oocytes in diplotene arrest, thecal layers, lampbrush chromosomes, and complete layers of follicular cells. The medulla is an elaborated complex of vascularized lacunae underlying the cortex and often containing discrete lymphoid aggregates. While the general morphology of the alligator ovary is similar to that of the chicken ovary, the progression of oogenesis and folliculogenesis around hatching is notably slower in alligators. Diplotene oocytes are observed at hatching in chickens, but not until 3 months in alligators. Folliculogenesis is completed at 3 weeks in chickens whereas it is still progressing at 3 months in alligators.

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

“…Although the location of synthesis of these factors is unknown in the pre-follicular crocodilian ovary, we can compare spatial expression patterns in other vertebrates with morphologically similar ovaries (Moore et al, 2008) to formulate a hypothesis. Steroidogenic cells differentiate and migrate from the nephrogenous mesenchyme in chicken and mouse ovaries (Sekido and Lovell-Badge, 2007).…”

“…Follicle assembly occurs slowly over many months post-hatching (Forbes, '40; Moore et al, 2010b, 2008), and the mechanisms regulating this process are being investigated. In mice, follicle assembly occurs over the first 3 days postnatal and some of the signaling mechanisms that regulate follicle assembly are becoming clear.…”

Molecular Mechanisms of Sex Determination in Reptiles

“…Primordial follicles form when a single layer of granulosa cells surrounds individual oocytes. The timing of meiosis initiation and follicle formation is species-specific, but usually occurs late in fetal life or shortly after birth [Moore et al, 2008]. Primordial follicles remain quiescent until females reach sexual maturity.…”

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

“…As observed in previous studies, newly hatched alligator gonads are not quiescent [Guillette et al, 1994;Milnes et al, 2008;Moore et al, 2008]. Analogous to the importance of appropriate mammalian follicle assembly [Bristol-Gould et al, 2006] or post-natal Sertoli cell proliferation [Buzzard et al, 2003], we propose that the mRNA expression levels and concomitant morphological changes observed here affect the establishment of alligator reproductive health and later fertility.…”