Biology Reference
In-Depth Information
5
Highlights and Directions
Le Page et al. (2010) have indicated that in mammals sex is decisively
determined by a single
Sry
gene located on a morphologically distinguishable
sex chromosome. In fi shes sex determination remains indecisive, as it is
determined by many genes (e.g., Hale et al., 2010; Loukovitis et al., 2010;
Shirak et al., 2006) located on different and not readily distinguishable
chromosomes (e.g., Bradley et al., 2011); some of these genes are drastically
infl uenced by endocrines and similar chemicals (Pandian et al., 2012)
as well as biotic (social) and abiotic (e.g., temperature, Pandian et al.,
2012) factors. In this context, it is interesting to note that many leading
scientists (e.g., Herpin and Schartl, 2011) have concluded that many (sex
determining) genes at the top of the genetic cascade are not conserved,
while the downstream genes are homologous in a much broader spectrum
of fi shes. Hence the need for genome-wide linkage analysis and search for
more than one sex determining gene residing on different chromosomes
of fi shes is emphasized.
Le Page et al. (2010) have proposed that non-sexualization of the brain
is the root cause for the plasticity in sex differentiation in fi shes. However,
this may hold true only for all sex changing hermaphrodites and secondary
gonochores alone. The brains of primary gonochoric fi shes are indeed
sexualized on or before the juvenile/pubertal stage. This conclusion is based
on: (i) all the phenotypic morphotypes undergo intrasexual ontogenetic
change suggesting brain sexualization in them, (ii) PGCs from embryos and
OSCs/SSCs from differentiated gonad drawn from mature adults that have
already spawned/milted, when transplanted into undifferentiated gonads
of recipients, express bisexual potency. However, the transplantation of SSCs
into sterilized adult testis containing germ cells supporting cells differentiate
into testis alone; this clearly indicates that the germ cells supporting somatic
