Differentiation in Gonochores - Genetic Sex Differentiation in Fish - page 63

Table 17. Land mark events in anatomical sex differentiation in ovary and testis in Oryzias
latipes (compiled from Suzuki and Shibata, 2004)

Age (dah) Ovary Testis

20-30 Cell layers at posterior end of ovary

are extended. Cell layers and mass,
ventral to ovary differentiate into
ovarian cavity and oviduct (Fig. 19A,
B, 20E)

PGC supporting somatic cells
develop as acinus precursors,
which differentiate into efferent
duct and sperm duct (Fig. 20B).
Urethra is developed ventral to
sperm duct (Fig. 20C).

31-50 UGP of medulla becomes apparent

and is connected with mesenchyme
cell layer between anus and urinary
pore (Fig. 19C,D)

Typical UGP medulla is
observed. Posterior end of
urethra (Fig. 20D).

51-90 Two layers originate from each side of

cortex. They invaginate into ventral
region of the mesenchyme and form
cavities namely genital lip, a female
specifi c feature (Fig. 19C,D). Fusion
of the cavities open into oviduct
anteriorly and to exterior posteriorly.
Prominent UGP is bi-or trilobed
(Fig. 19E) GPL is located dorsal to
UGP medulla.

Spermatogenesis and sperm are
observed. Epithelia of anterior
sperm duct and urethra are
nearer to urinary pore
(Fig. 20D).

fadrozole, an aromatase suppressant, severely inhibited the formation of
ovarian cavity and anterior oviduct (Suzuki et al., 2004).
Incidentally, amh/mis is responsible for the regression of Mullerian ducts
in the mammalian male fetus. The role of mis in gonadal sex differentiation
in fi shes, which have no Mullerian ducts, remain unclear. Shiraishi et al.
(2008) have shown that mis and mis type2 receptor ( misr2 ) mRNA are
expressed in somatic cells surrounding the germs cells of both sexes during
sex differentiation of medaka. Germ cell proliferation is suppressed by
the loss of either mis or misr2. When tissue fragments containing germ
cells are treated with recombinemt eel mis, the germ cells proliferate more
signifi cantly in both sexes, compared with the untreated control. In contrast,
culture tissue fragments from the mis or misr2 defective embryos inhibit
the proliferation of germ cells in both sexes. In medaka, mis indirectly
stimulates germ cell proliferation through misr2 expressed in somatic cells
immediately after they reach the gonadal primordium. However, Dmrt
may play an important role in dimorphic sexual differentiation of germ
cell proliferation.
Though inappropriate, differentiation of genital ducts in a protandric is
briefed to provide a continuity. The black porgy Acanthopagrus schlegeli has
a striking life cycle, including an early sex differentiation, bisexual gonad
and male to female natural sex change. According to the description by
Lee et al. (2011), the gonads develop 'ovarian cavity cracks' and become
'four stranded' at the age of 16 weeks. Subsequently, genital ducts are