Dimorphic Expression of Various Transcription Factor and Steroidogenic Enzyme Genes during Gonadal Ontogeny in the Air-Breathing Catfish, <i>Clarias gariepinus</i>

Abstract

In the present study the expression of 13 genes known to be involved in sex differentiation and steroidogenesis in catfish was analyzed during gonadal ontogeny by quantitative real-time RT-PCR. Dmrt1 and sox9a showed exclusive expression in male gonads while ovarian aromatase (cyp19a1) and foxl2 were abundant in differentiating female gonads. Most of the genes related to steroidogenesis were expressed only after gonadal differentiation. However, genes coding for 3β-hydroxysteroid dehydrogenase (3β-hsd), 17α-hydroxylase/C17–20 lyase type 1 (cyp17) and steroidogenic acute regulatory protein (star) were barely detectable during gonadal differentiation. Ovarian aromatase, cyp19a1, which is responsible for estradiol-17β biosynthesis in females, was expressed very early in the undifferentiated gonads of catfish, around 30–40 days post hatch (dph). The steroidogenic enzyme, 11β-hydroxylase (cyp11b1) required for the production of 11-ketotestosterone (11-KT) was expressed only after differentiation of testis. These results suggest that estradiol-17β has a critical role in ovarian differentiation, while the role of 11-KT in testicular differentiation is doubtful. In conclusion, dimorphic expression of dmrt1 and sox9a in gonads during early development is required for testicular differentiation, and sex-specific expression of cyp19a1 and foxl2 in females plays a critical role in ovarian development. Our study reveals that the critical period of gonadal differentiation in catfish starts around 30–40 dph when sex-specific genes showed differential expression.

Expression Analysis of <b><i>sox3</i></b> during Testicular Development, Recrudescence, and after hCG Induction in Catfish, <b><i>Clarias batrachus</i></b>

“…However, the present study showed the dimorphic expression of sox3 during gonadal development and differential expression during the seasonal cycle in a gonochoristic fish model. Sox3 expression was noticed in both male and female developing gonads in C. gariepinus [Raghuveer et al, 2011], while the present study showed expression changes during gonadal development in comparison to adult fishes. In catfish, the immature testis and ovary showed higher sox3 expression than the mature testis during ontogeny, which confirms the more important role of Sox3 in gonadal development and maturation during early stages than in the adult fish.…”

“Brain sex differentiation” in teleosts: Emerging concepts with potential biomarkers

“…To delineate female brain sex development/differentiation, in depth studies on the development of the CAergic system during male and female brain sex development of air-breathing catfish, Clarias batrachus demonstrated gender specific differences where female brain showed higher level of tyrosine hydroxylase (Th) expression with high copy numbers as compared to males (Mamta et al, 2014; Table 1). Brain Th ontogeny also revealed higher transcript levels in female brain at 50, 75 and 100 dph as compared to male brain at same age groups (Mamta et al, 2014; Table 1) wherein 50 dph is the critical period for gonadal sex differentiation in catfish (Raghuveer et al, 2011a). These findings were further correlated with the levels of NE and DA which also showed sexual dimorphism (Mamta et al, 2014).…”

Diversity and Plasticity of Sex Determination and Differentiation in Fishes

“…Many studies on the ontogenic expression of Foxl2 have been carried out in vertebrates [Baron et al, 2005;Yao, 2005]. These studies revealed Foxl2 as one of the earliest markers of ovarian differentiation in vertebrates [Schlessinger et al, 2010;Raghuveer et al, 2011]. As in mammals, the mRNA of P450arom and Foxl2 were found to be co-localized in the ovaries of adult medaka [Nakamoto et al, 2006], tilapia [Wang et al, 2004], and flounder [Yamaguchi et al, 2007].…”