Differentiation in Gonochores - Genetic Sex Differentiation in Fish - page 91

positive PGCs expressed abundantly in the gonads but its fl uorescence
began to diminish with the advancing spermatogonial process. Based on Gfp
intensities, tubicular cells were divided into a few fractions. Of them ritili
is used to isolate spermatogonia A type. Lacerda et al. (2006) injected 2 ml
of suspension containing 5x10 6 cells/ml, while Okutsu et al. transplanted
only 18,000 cells containing 10,000 SSCs.
OSCs from the dominantly orange body colored transgenic rainbow
trout carrying pVasa - Gfp were dissociated and concentrated OSCs
fl ow cytometrically were isoloated. From this ovarian cell suspension,
20-30 nl containing 15,000 cells including about 100 OSCs were used for
transplantation.
Vasa : The RNA helicase vasa is a germ cell marker in animals and its
homologue in vertebrates to date is considered as limited to bisexual
reproduction, although it remains unclear with reference to sequential
hermaphroditic fi shes, which mature fi rst either as females (protogyny)
or males (protandry) and subsequently change to the opposite sex. Xu
et al. (2005) have cloned Cag Vasa , a Vasa homologue, from the gibel carp
Carassius auratus gibelio , a fi sh known to shift between gono- and gyno modes
of reproduction. In bisexually reproducing gibel carp, vasa is maternally
provided (see Pandian, 2011) and its zygotic expression is restricted to
gonads. Following the dynamic sub-cellular distribution, vasa RNA is
found most signifi cantly in spermatogonia and spermatocytes entering
or undergoing meiosis but not in meiotic products namely the spermatids
and sperm, as against the continued low-high-low presence throughout
oogenesis from oogonia through vitellogenic oocytes to maturing oocytes.
The sequence of differential expression of vasa RNA and its protein in
oogenesis and spermatogenesis in gibel carp is also common to medaka,
tilapia (Kobayashi et al., 2000) and zebrafi sh (Knaut et al., 2000, 2002).
These fi ndings reveal that oogonial cells have retained sexual plasticity
throughout oogenesis from oogonia to mature oocytes, whereas it is limited
to the primary and secondary spermatocytes alone. Incidentally, a fi rst line
normal spermatogonial stems of medaka fi sh has been established and the
line has retained the competence to long-term self-renewal and test-tube
sperm production (Hong et al., 2004).
In an attempt to understand the genetic mechanism of differentiation
in the gono- and gyno-gibel carp C. auratus gibelio , Du et al. (2008) found no
expression of Hira (histone regulation) transcription in the liver of gyno-carp
but a high level of Hira RNA in gono-carp. They suggested that the Hira
may be associated with different modes of reproduction in the carp. Wu et
al. (2009) cloned a novel oocyte-specifi c variant H2A implying a possible
association between chromatin structure and reproduction of the gibel carp,
which can switch between gynogenic and bisexual modes of reproduction.