Differentiation in Gonochores - Genetic Sex Differentiation in Fish - page 57

females with predominance of vitelloginic follicles are perhaps involved in
arresting prophase I of the meiotic division of most germ cells in the early
oocyte stage. This may be a reason for the reductions in relative fecundity
and relative fecundity rate observed in aged female fi shes (cf. Fig. 27).
In recent years a number of reports on the mutants in zebrafi sh reversing
its sex have been published. For instance, Abrams and Mullins (2009)
considered only the maternal defective mutants, indicating the occurrence of
>40 unique mutants to confi rm the maternal control of early differentiation
in zebrafi sh. Table 16 lists some of these mutants relevant to sex reversal
during embryonic and post-hatching stages in zebrafi sh.
Table 16. Selected examples of mutants and their role in sex differentiation in zebrafi sh

Mutant Remarks

Ziwi Reduces the number of PGCs (cf Saito et al.,2008) leading to production of

all male progenies (Houwing et al., 2007)

Fancl Expresses in developing germ cells of bipotential gonads at the critical

time of sex differentiation. Caspase 3 immuno assay reveals the increased
apoptosis of germ cells in homozygous mutants leading to production
of all male progenies. On failure of oocytes to survive through meiosis,
the PGC supporting somatic cells fail to express the ovarian gene cyp19la
nor the consequent down-regulation of the testis gene amh. However, the
introduction of tumor suppressor gene tp53 into fancl mutants rescues
production of females, indicating that fancl is involved only with survival of
developing oocytes through meiosis (Rodrequez-Mari et al., 2010)

Brca Q658X Homologue of BRCA2 mutant in human with hereditary breast and ovarian

cancer. Brca Q658X induces the failure of embryonic differentiation of oocyte
of zebrafi sh. Oogenesis proceeds normally but produces binucleate oocytes
(Shive et al., 2010)

2.6d Silurus meridionalis

Only fragmentary information is available on genes responsible for
morphological and molecular sexual dimorphic differentiation in this
catfi sh. Yet, it seems to provide an interesting but a different differentiation
process and calls for further study on the role of sex differentiation genes
from zero dah. Information on the gamety of the catfi sh, as well as whether
the catfi sh belongs to the tertiary gonochore, in which potential intersexual
gonad, develops directly into either an ovary or a testis is required. In
gonochoric teleosts, the initial ovarian ontogeny varies with species and is
fi rst indicated either by the appearance of the ovarian lumen or by germ
cell meiosis (Nakumara et al., 1998). In Cichlasoma dimerus, O. latipes, and
A. anguilla, the entrance of oogonia into meiotic division and development
of primary growth stage oocytes occur prior to the formation of the ovarian
lumen but it is after the formation of the lumen in P. olivaceus, P. lethostigma,
O. niloticus and O. aureus (see Luckenback et al., 2003). Apparently,