Onset Of Gonadal Differentiation Research Articles

Foxl2 is required for the initiation of the female pathway in a temperature-dependent sex determination system in Trachemys scripta

ABSTRACT KDM6B-mediated epigenetic modification of the testicular regulator Dmrt1 has previously been identified as the primary switch of the male pathway in a temperature-dependent sex-determination (TSD) system; however, the molecular network of the female pathway has not yet been established. Here, we have functionally characterized for the first time an upstream regulator of the female pathway, the forkhead transcription factor FOXL2, in Trachemys scripta, a turtle species with a TSD system. FOXL2 exhibited temperature-dependent female-specific expression patterns before the onset of gonadal differentiation and was preferentially localized in ovarian somatic cells. Foxl2 responded rapidly to temperature shifts and estrogen. Importantly, forced expression of Foxl2 at the male-producing temperature led to male-to-female sex reversal, as evidenced by the formation of an ovary-like structure, and upregulation of the ovarian regulators Cyp19a1 and R-spondin1. Additionally, knockdown of Foxl2 caused masculinization at the female-producing temperature, which was confirmed by loss of the female phenotype, development of seminiferous tubules, and elevated expression of Dmrt1 and Sox9. Collectively, we demonstrate that Foxl2 expression is necessary and sufficient to drive ovarian determination in T. scripta, suggesting a crucial role of Foxl2 in female sex determination in the TSD system.

Differentiation and Development of Gonads in the Yellow-Bellied Toad,Bombina variegataL., 1758 (Amphibia: Anura: Bombinatoridae)

The aim of this study was to investigate consecutive stages of gonadal development of the yellow-bellied toad (Bombina variegata) with particular emphasis on the origin of somatic and germ cell lineages as well as the timing of gonial cell migration. Changes in gonadal basal lamina distribution helped to explain the exceptional mode of gonadal differentiation in this species. Atypical and rapid differentiation of the male gonad in B. variegata is the result of the ability of gonial cells to migrate into the center of the gonad relatively early. Thus, the testis medulla contains germ cells from the onset of gonadal differentiation into cortex and medulla, whereas in other anurans a sterile medulla is characteristic of both future testes and ovaries; germ cells translocate into the medulla during the subsequent stage of testis development. This atypical testiculogenesis is probably the result of an acceleration of the sex determination period, indicating a contribution of sex determination heterochrony to the course of gonadogenesis. The results also suggest that medullar cells are derived from proliferating coelomic epithelial cells. Moreover, Sertoli cells constitute an integral part of the germinal epithelium in B. variegata, as in other vertebrates. Spermatids do not contact Sertoli cells just before spermiation and do not form bundles.

Temporal profile of brain and pituitary GnRHs, GnRH-R and gonadotropin mRNA expression and content during early development in European sea bass ( Dicentrarchus labrax L.)

A likely endocrine control mechanism for sexual differentiation in size-graded populations of European sea bass ( Dicentrarchus labrax) is proposed by evaluating the brain expression and pituitary content of two forms of gonadotropin-releasing hormone (GnRH), namely sea bream (sbGnRH) and salmon (sGnRH), the pituitary expression of one subtype of GnRH receptor (dlGnRH-R-2A) and the three gonadotropin (GtH) subunits, namely glycoprotein α (GPα), follicle-stimulating hormone β (FSHβ) and luteinizing hormone β (LHβ), as well as the pituitary and plasma LH levels between 50 and 300 days post-hatching (dph). Four gradings were conducted between 2 and 8 months after hatching, resulting in a population of large and small individuals, having 96.5% females (female-dominant population) and 69.2% males (male-dominant population), respectively, after the last grading. The onset of gonadal differentiation was different in the two sexes, and coincided with a peak of expression of sbGnRH or sGnRH. Furthermore, the expression of these GnRHs was correlated with the expression of dlGnRH-R-2A. Sex-related differences in the brain and pituitary content of sbGnRH were also found at the time of sexual differentiation. Moreover, the observed sexual dimorphism at the transcriptional or synthesis level of these GnRH forms suggests that a different neuro-hormonal regulation is operating according to sex. At the onset of sex differentiation, FSHβ transcriptional activity reached maximal values, which were maintained until the completion of the process. The present study suggests a role for sbGnRH, sGnRH and the dlGnRH-R-2A during gonadal differentiation, possibly through enhancement of FSHβ gene expression. In males, a different endocrine regulation seems to exist also during spermiogenesis and spermiation, when gene transcription, peptide synthesis and release of LH are of greater importance.

Gene expression of sex-determining factors and steroidogenic enzymes in the chicken embryo: influence of xenoestrogens

Many genes involved in gonadal development have been proposed for mammals. To elucidate if those genes play any critical role in sexual differentiation of the avian gonad, we have examined expressions of the genes for proposed sex-determining factors (SF1, Sox9, DMRT1, Wpkci, and AMH), steroidogenic enzymes (P-450scc, 3β-HSD, P-450c17, 17β-HSD and aromatase) and the estrogen receptor in the urogenital system during chicken embryogenesis (days 4–16 of incubation), using a semi-quantitative reverse transcription-polymerase chain reaction. Transcripts of the genes for sex-determining factors except Wpkci and AMH were detected in both sexes but had no sexual dimorphism. Wpkci expression was female specific and constantly high throughout incubation. AMH was expressed in both sexes from the earliest stages but was higher in males than in females after the onset of gonadal differentiation. Expressions of the genes for more downstream enzymes in a steroidogenic pathway, such as P-450c17, 17β-HSD and aromatase, were clearly higher in females than in males. In particular, 17 β- HSD expression increased in the course of gonadal development in females, whereas it was constantly low in males. Aromatase was highly expressed in females during gonadal differentiation but not in males over the period. In addition, to elucidate the relationship between gene activation during embryogenesis and reproductive abnormalities in wild birds, we examined expressions of these genes in embryos treated with various doses of diethylstilbestrol (DES), as a representative estrogenic compound. DES had no effect on the expressions of all the genes in either sex during the periods of gonadal differentiation (days 8, 12, and 16). Sexual dimorphism of the gene expression for steroidogenic enzymes appeared to be closely related to gonadal development in the chicken embryo, especially in the female. However, all the genes examined here seem unlikely to respond to xenoestrogens.

Temporal profile of the outer- and inner-ring iodothyronine deiodinase pathways in the liver and skin in developing rainbow trout Oncorhynchus mykiss

We measured the activities of iodothyronine-activating (D1 and D2) and -inactivating (D3) deiodinases, as well as the circulating levels of their corresponding substrates and/or products, T4, T3, and rT3, in the developing rainbow trout. The study was conducted through 20 consecutive months and included fry, fingerlings, and mature animals from 14 to 88 weeks post-hatching (ph). Initially, blood concentration of active iodothyronines was low and tissue D3 activity was greater than the activity of D1 and D2. As fry developed into fingerlings, the activity of liver D2 increased, while that of skin D3 declined. The time course of these changes was directly (T3) or inversely (rT3 and D3) correlated to an increase in age, length, and body weight. The initial increment in both circulating T3 and hepatic D2 activity during the first spring (March-April; weeks 46–50 ph) coincided with the onset of gonadal differentiation, whereas the highest values of T3 and hepatic D1 and D2 (September–October; weeks 70–74 ph) occurred at the onset of sexual maturity. These results suggest that a hepatic supply of active T3 is temporally associated with gametogenesis.

Developmental changes of the oestrogen receptor-alpha and -beta mRNAs in the female reproductive organ of the rat--an analysis by in situ hybridization

This study employed an in situ hybridization technique to compare the cellular expression of oestrogen receptor (ER) subtypes, ER alpha and beta, in the female reproductive organ of the rat during prenatal and postnatal periods. Diffuse signals of ER alpha and beta mRNAs were co-expressed in the foetal ovary; they were weak and inconsistent before onset of gonadal differentiation, but increased in intensity with age. ER beta mRNA signals in the ovary sharply increased in intensity to adult levels by postnatal days 6-7, whereas those of ER alpha mRNA remained unchanged after birth. ER alpha was the sole subtype expressed during the prenatal period from the oviduct to the vagina, being localized mainly to the sub-epithelial stromal cells, and remained predominant thereafter. Signals for ER alpha mRNA in the epithelia were confined to the oviduct during prenatal and early postnatal periods; those in uterine and vaginal epithelia first appeared by postnatal days 4-5 and 6 respectively. Expressions of ER beta mRNA in the reproductive tract were absent during the prenatal period, and were weakly expressed during the postnatal period. Thus, oestrogen action in the developing ovary may be co-mediated by both ER alpha and beta, whereas ER alpha may be the primary mediator in the differentiation and growth of the female reproductive tract.

Gene expression during gonadal differentiation in the rat: A two‐dimensional gel electrophoresis investigation

AbstractGonadal protein patterns were studied during development in the rat by two‐dimensional micro‐gel electrophoresis. Specific proteins were detected in both the male and the female sex at the morphologically indifferent state (two female‐ and one male‐specific) and during differentiation. At the onset of gonadal differentiation (day 14) two additional sex‐specific proteins were discovered in the male and two in the female. These proteins remained expressed during further development. One testicular protein was restricted to the cytosol of the tunica albuginea. The other one was absent from the tunica. In the female gonad, the two proteins were membrane‐specific, one present in germ cells, the other in somatic cells. In the testis, one additional protein was discovered at postnatal day 1. Thus according to biochemical criteria there is no indifferent state of gonadal development. The testis and ovary express sex‐specific genes both before and after the onset of gonadal differentiation.