Biology Reference
In-Depth Information
by Vtg EIA, while 100% of immature females and 95% of adult males are
accurately sexed by 17β estradiol and 11-KT ratios (Chu-Koo et al., 2009).
With reference to macroandry, the identifi cation of
growth hormone
pseudogene
in male salmonids is relevant (Table 9) but more details on
this aspect are provided elsewhere (Pandian et al., 2012). Interestingly,
on transplantation of Spermatogonial Stem Cells (SSCs) into the sterile
alevins of triploid masu, the fertile xenogenic masu also displays nuptial
body coloration and males with an elongated jaw, both of which are typical
secondary sexual characters. For the other sex specifi c characters, more
details can be obtained from Pandian (2010). The genetic mechanism of
differentiation of most of these secondary sexual characters need to be
studied. Nevertheless the morphological and molecular differentiation
of gonopodium has received attention since 1938. Viviparity is usually
facilitated by an intromittent organ namely gonopodium in Poeciliidae,
andropodium in Herniramphidae, priparium in Phallostethidae, penes in
Cottidae, tubular genital papillae in Athernidae or anal fi ns in
Corynopoma
riisei
(Burns et al., 1995). The anal fi n of goodeids is modifi ed into a primitive
gonopodium, which is not structurally and functionally similar to that in
poeciliids (Bisazza, 1997).
Secondary sexual characters generally appear at puberty. The formation
of gonopodium in poeciliids offers an entry point to understand the sexual
differentiation in juveniles. Anal fi ns of male and female juveniles (<10
mm) of
Gambusia affi nis
are identical (Turner, 1941). When a male reaches
a body length of 15 mm and larger size, the anal fi n rays 3, 4 and 5 are
greatly elongated with increased number of segments from about 15-20
to 38-43; besides, the 4th and 5th rays are bifurcated, and adorned with
elbow, serrae, spines and terminal hooks (Fig. 26), while all the other rays
remain short. In the female, the fi ns remain short but the 4th and 5th rays
are bifurcated and a little elongated. More details on cell proliferation, and
further differentiation are described by Ogino et al. (2004).
In
G. affi nis,
Ogino et al. (2004) have also cloned two
ar α
c
DNA
and
identifi ed them as
ar α
and
ar β
. Both are strongly expressed prominently
in the distal region of outgrowing anal fi n rays;
ar α
is expressed in both
epithelium and mesenchymal regions of the anal fi n, while that of
ar β
in
the distal mesenchyme and outgrowing fi n rays. The signaling molecule,
sonic hedgehog
(
shh
) induces the development epithelium of distal anal fi n
rays.
shh
participates in differentiation or regeneration of fi ns with
Ptc1
receptor, whose expression is also detected adjacent to the
shh
-expressing
region. Administration of androgen induced anal fi n outgrowth concomitant
with the
shh
induction to the formation of a gonopodium. The functions
of
ar
in the formation of intromittent organ in other fi shes are indicated by
Ogino et al. (2011).
