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especially 11-KT, the potent androgen of males. The p450 11β cDNA
has been cloned in
A. japonicus
(Jiang et al., 1996),
O. mykiss
(Liu et
al., 2000) and
D. labrax
(Socorroa et al., 2007). In the trout, p450 11β is
expressed specifi cally during testicular differentiation (Baron et al.,
2005b). Androgens such as testosterone, DHT, or 11-KT have no direct
effect on regulation of
cyp19a1b
expression in the brain of zebrafi sh
(Mouriec et al., 2009).
(vii)
foxl2
is a
forkhead
box transcription factor (Hannenhalli and Kaestner,
2009) and is a female specifi c gene known to induce the earliest
dimorphic sexual differentiation. It directly binds testis specifi c
sox9
enhancer element (TESCO) and silences the
sox9
expression
in the ovaries (Uhlenhaut et al., 2009). Hence
fox12
is a suppressor
of testes fate. It regulates the expression of
p450 arom
during sexual
differentiation and signals the transcriptional regulation of
cyp19a1
(Yamaguchi et al., 2007). In
S. meridionalis, foxl2
is found to be
expressed extensively in the brain and pituitary and with the highest
level in the ovary, indicating the possible involvement of
foxl2
in the
brain-pituitary-ovary axis (Liu et al., 2007). The association of
foxl2
SNP (Single Nucleotide) polymorphism in
P. olivaceus
has shown
that the SNP1 in the forkhead domain is signifi cantly associated with
gonado somatic index (GSI), SNP2 downstream forkhead domain
with serum 17β-estrodiol (E
2
) level and SNP3 in the 3'- UTR with
hepatosomatic index (HSI) (Shi et al., 2009).
(viii)
DaxL
is atypical of the family of nuclear receptors to hormones and
is linked to chromosome XX in mammals (Zanaria et al., 1994). It has
been isolated and characterized in many fi shes, e.g.,
O. mykiss
(Baron
et al., 2005a),
Dicentrarchus labrax
(Martins et al., 2007) and
Squalius
alburnoides
(Pala et al., 2009). It is known not to express in germ cells
but in Sertoli cells and in follicular cells surrounding perinuclear
oocytes in the adult female
S. alburnoides
(Pala et al., 2009).
(ix)
fi g α
: is a germ cell specifi c transcription factor required for ovarian
follicle formation. The expression of
fi g α
and z
pe
coincides with the
onset of gonadal differentiation in zebrafi sh (Jorgensen et al., 2008).
Many genes, which are more known in the genetic cascade of
mammals, may soon be identified and characterized in fishes.
Some examples are the
fi gl α
, which are expressed in Sertoli cells
of
S. alburnoides
(Pala et al., 2009), and
tbx1a
, a homologue of
tbx
,
is highly expressed in somatic cells surrounding germ cells of the
differentiating testis of
O. mykiss
(Yano et al., 2011). In fi shes the
existence of
shbga
and
shbgb
encoding different proteins are reported.
Shbga,
the mammalian homologue of
shbg,
found in almost all teleosts,
