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within 6 months (Fig. 37). The presence of donor-derived gametes has
been confi rmed by PCR in 20% recipient males of Patagonian pejerrey.
On crossing these xenogenic males with pejerrey females, the progenies
are either hybrids or pure pejerreys with donor-derived germline at the
frequencies of 1.2 to 13.3%. Hence the transplantations of SSCs into the
sterile adult male allogenic
O. niloticus
and that of
O. bonariensis
into sterile
adult male xenogenic
O. hatcheri
have resulted in the production of males
only, i.e., apparently, the germ cells supporting somatic cells have lost
bisexual potency and the hormonal micro-climate prevalent in the adult
sterile testis allow the SSCs with bisexual potency to express unisexual
potency, i.e., develop testis alone.
In this context, a publication by Tagami et al. (2007) becomes relevant.
They have transplanted 'W' bearing PGCs into male recipient embryos,
and the female PGCs have colonized the recipient's gonad. In the 'testis'
of allogenic the female PGCs have been differentiated into spermatogonia
(30.8%), spermatocytes (32.7%), spermatids (28.4%) and spermatozoa (0.2%).
Hence the female PGCs in the testis of the allogenic cock successfully pass
through the fi rst and second meiotic divisions but are hardly capable of
spermeiogenesis.
While the technical feasibility of allogenesis and xenogenesis and their
potentials are of great signifi cance, research in this area demands very
sophisticated techniques and high skills for cell transplantation. Further, the
xenogenics may take a considerably long time to mature and undertaking
progeny testis. As an alternative, the Brazilian group led by C Franca used
a sterile male as a recipient. Lacerda et al. (2006) have claimed that their
allogenics of
O. niloticus
have developed testes from the donor-derived
SSCs,
albeit
without having undertaken progeny testing. In a subsequent
experiment, the SSCs, isolated from red Nile tilapia were transplanted into
the busulfan-treated adult testis of gray colored Chitralada tilapia (Lacerda
et al., 2010). Fluoresence microscopic evidence showed that the transferred
donor germ cells effi ciently colonized the testis and generated PKH26-
labeled spermatogenic cysts and ultimately formed mature spermatids
and spermatozoa. DNA microsatellite analysis revealed the presence of
donor-derived alleles in 6.3% of the F
1
progeny (Fig. 37).
The results obtained in all these experiments seem to indicate the
following: 1. Competing against the respective endogenous PGCs, the
colonizing effi ciency of the donor-derived OSCs in allogenic trout is about
41-47%. Among the mature allogenics, 5% females were fertile, as against
15% fertile males. But the fertility of the xenogenic trout was as high as 84%
for males and 10% for females. It is not known whether the competence to
differentiate into fertile ovary by both OSCs and SSCs is signifi cantly lower
than that to differentiate fertile testis in allogenic as well as xenogenics, or
