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to about 100 at the 20 dph fry (Fig. 13). To have a better insight into the
role played by tDmrt1 'as superior molecular marker' of inducing male
differentiation in tilapia, Kobayashi et al. (2008) have treated XX tilapia fry
with 17α-methyltestosterone (MT) from 6 to 14 dph. The mean number of
PGC cells in the MT-treated XX fry is 98 and is less than that (135) in the
normal XY fry. Hence the MT dose-dependent sex reversal is accompanied
by sex specifi c tDmrt1 expression. Incidentally, similar trends of faster and
slower proliferation of PGCs in female and male embryos of the cyprinid
rosy barb Puntius conchonius have been reported by Cek et al. (1998).
In the untreated normal Nile tilapia fry, the tDmrt1 signals become
localized in Sertoli cells and epithelial cells of intratesticular efferent duct,
recalling similar events in the DMY induction in O. latipes . When the
formation of the intratesticular efferent duct anlage is apparent at 25 dph
(Fig. 14), the tDmrt1 expression is detected in Sertoli cells, medullary mass
and its derivative the intratesticular epithelial cells of efferent duct. Using
laminin antibody, tDmrt1 positive cells have been found only within the
Fig. 14. Sexual dimorphism during gonadal differentiation in Oreochromis niloticus . Schematic
representation of gonadal histogenesis during gonadal differentiation. CE = coelomic
epithelium, GGC = gonial germ cell, SPC = steroid producing cell, BV = blood vessels, OVC =
ovarian cavity, pED = anlage of intratesticular efferent duct, Oc = oocyte, ED = intratesticular
efferent duct, M = medullary cell, I = interstitium (from Kobayashi, 2010, reproduced with
permission by The International Journal of Developmental Biology, 54: 105-111)
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