Expression profiling of various marker genes involved in gonadal differentiation of teleosts: Molecular understanding of sexual plasticity

Abstract

Undifferentiated gonads transforming into either testis or ovary is an important eventin the developmental processes of vertebrate sex determination and differentiation.Molecular mechanisms underlying this phenomenon revealed involvement of severaltranscription factors, signaling molecules or receptors and steroidogenic enzymes, whichare eventually designated as marker genes/factors. Expression profiling of these markergenes using various teleosts models indicated sexually dimorphic or differentialexpression during gonadal differentiation. In this review, we highlight the functionalrelevance of certain eventful biomarkers to our molecular understanding of sexualplasticity in teleosts. Among the marker genes, dmrt1 and sox9a showed exclusiveexpression in differentiating testis while expression of ovarian aromatase, cyp19a1a andfoxl2 was prolific in developing ovary. Interestingly, in certain species like tilapiaexpression of cyp19a1a was evident even in undifferentiated gonads of XX females.Similarly, exclusive expression of sox9b in ovary was evident in few teleosts includingcatfish. Pioneering studies in several teleosts demonstrated the expression of vasa prior tosexual development which eventually regarded vasa as potential germ cell marker.Transcription factor such as Wt-1, signaling molecule such as Wnt-4 and orphan nuclearreceptors such as Ad4BP/SF-1, Dax-1 and SHP showed certain degree of differentialexpression, if not absolute sexual dimorphism during early development. Reports on thefate of these genes after sexual differentiation revealed significant association of some ofthese correlates during recrudescence and reproductive cycle. One of the necessities in the present arena is just not depending on the correlative response of marker genesinstead focusing on designing novel experiments to signify specific roles like thosedetermined for DMY/dmrt1 or cyp19a1a. To enable this, innovative studies in severalteleosts using morpholino or siRNA or knock-out/exploitation of normal mutants willfurther contribute on our molecular understanding of sexual development cascade. In thiscontext, natural or artificial sex reversal experiments might also provide new researchprospects. Nonetheless, in the present scenario, identification of marker genes providedtremendous application potential to examine impacts of endocrine disruptors at molecularlevel. © 2013 Nova Science Publishers, Inc.