Among thereby an important factor in the

Among all vertebrates fishes
exhibit  greatest diversity in species
and act as a relevant model for genetic and evolutionary studies. A common
feature observed in most  of several fish
species is hermaphroditism. It was observed that few genes have been
linked in the process of sex determination or differentiation as in zebra fish.
The genes Fushi Tarazu factor-1 (FTZ-F1)
play crucial role as they were involved in regulating interrenal development  as well as expression patterns similar with
reproductive tissue differentiation. For
most of the fish species the differentiation of gonad into a testis or an ovary
is strongly influenced by hormonal,
environmental or social factors. In the studies it was observed that they can
be sex reversed by exposure to estrogens, suggesting that the estrogen levels
play a crucial role during sex differentiation. In certain studies in zebra
fish it was observed gonadal sex differentiation occurred due to the compounds
that interfere the with cyp19 gene expression. The Cyp19 gene product aromatase
usually converts testosterone into 17 beta-estradiol but when inhibited leads
to male to female sex reversal. FTZ-F1 genes involved in  steroid biosynthesis and  regulatory region of Cyp19 contains binding
sites for FTZ-F1 genes, that are involved in sex differentiation process 44. The Dax-1 gene has however
been identified in the Nile Tilapia 18, 45, suggesting that other
fish species may also have Dax-1 homologues that play a role in sex
differentiation. The
double sex and mab-3 related (DM) transcription factor 1 (dmrt1) plays a very
important role in testicular differentiation. Several HMG-box containing genes,
Sox-genes, have been identified in fish 46-48. Those transcription
factors include dmy,sd4BP/SF1,sox9,dax1 and wt1 that plays crucial role in sex
determination and differentiation. It was found that HMG-Box cis element has
been identified in gene promoter of fushi tarazu factor 1a
(ff1a) 49. It was also observed that
Sox9 alone does not direct sex determination and differentiation in zebra fish.
AMH inhibits the expression of aromatase in the developing gonads 50 therefore negatively
controlling the differentiation and function of Leydig cells by down regulating
enzymes that are involved in the steroidogenic pathway 51. WT1 has been shown
to be expressed in the intermediate mesoderm earlier to and during renal tissue
differentiation 52. It is also essential for
the steroidogenic interrenal development together with ff1b 53, 54. WT1 is thereby an
important factor in the early events during development of gonadal primordium.
Dmrt1 also play an important role in testis determination in teleosts, as the
levels of  aromatase enzyme differ during
sex differentiation can cause sex reversals 55. These Dmrt is usually
regulated by GATA factors. GATA factors processes the binding sites of cyp19
gene promoter that indicates its role in regulating aromatase expression 56, 57.