Dimorphic expression of tryptophan hydroxylase in the brain of XX and XY Nile tilapia during early development

Department of Animal Sciences, School of Life Sciences-Centre of Advanced Study, University of Hyderabad, P.O. Central University, Hyderabad 500046, Andhra Pradesh, India.
General and Comparative Endocrinology (Impact Factor: 2.47). 11/2009; 166(2):320-9. DOI: 10.1016/j.ygcen.2009.11.009
Source: PubMed


Serotonin (5-HT) is well known for modulating the release of GnRH and gonadotropin in teleosts. Reports on increased female:male ratio after the blockade of 5-HT biosynthesis proposed a role for 5-HT in brain sex differentiation. Two types of tryptophan hydroxylase (Tph), rate-limiting enzyme in the biosynthesis of 5-HT were cloned from vertebrates. In the present study, we cloned Tph from brain and evaluated its importance during early development of XX and XY Nile tilapia. Tph cloned from tilapia brain is 1888 bp in length and it encodes predicted protein of 462 amino acid residues. Tph activity of tilapia was confirmed by demonstrating the conversion of L-tryptophan to 5-hydroxy tryptophan by the recombinant protein after transient transfection of this cDNA clone in COS-7 cells. Northern blot identified single transcript around 2kb in male brain. Tissue distribution of Tph revealed high abundance in brain, kidney, liver and testis. Semi-quantitative RT-PCR revealed exclusive expression of Tph in the male brain from 5 to 20 days post hatch (dph) while in the female brain, it was from 25 dph. These results were authenticated by localization of Tph transcripts in olfactory bulb-telencephalon region of 11 dph male brain using in situ hybridization. Tph immunoreactivity (-ir) was also evident in the nucleus preopticus-periventricularis area of male brain as early as 12 dph. However, Tph-ir was observed in several regions of both male and female brain without any distinction from 30 dph. Dimorphic expression pattern of Tph during early brain development around the critical period (7-21 dph) of gonadal sex determination and differentiation may implicate a role for Tph in brain sex differentiation of tilapia.

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Available from: Deshou Wang, May 18, 2015
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    • "In this context, our previous reports showed variations in GnRH–GTH immunoreactivity in genetic XX and XY populations of the Nile tilapia (Sakai et al., 2005; Swapna et al., 2008). Consequently, the sexual dimorphic expression of tph was observed during early development in the Nile tilapia and catfish (Raghuveer et al., 2011; Sudhakumari et al., 2010). Subsequent analysis also revealed high levels of 5-HT in the brain of developing males undergoing gonadal sex differentiation (Raghuveer et al., 2011). "
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    • "Sterol transfer protein, star delivers cholesterol from cytoplasm to mitochondria, which is a rate-limiting step in steroidogenesis (Stocco, 2000). Having found that endosulfan and flutamide create adverse estrogenecity by specifically enhancing the E 2 production, our study also aimed to analyze the impact on catfish GnRH and tph2 as they are potential targets to reveal altered E 2 feedback (Tsai et al., 2000; Swapna and Senthilkumaran, 2009; Sudhakumari et al., 2010; Raghuveer et al., 2011b). Tph, a homotetrameric enzyme, is involved in the rate-limiting step of serotonin (5-HT) biosynthesis (Boadle-Biber, 1993). "
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