R. Brawtal et al., FOLLISTATIN BUT NOT ALPHA-INHIBIN OR BETA(A)-INHIBIN SUBUNIT MESSENGER-RNA IS EXPRESSED IN OVINE FETAL OVARIES IN LATE-GESTATION, Journal of molecular endocrinology, 13(1), 1994, pp. 1-9
The aim of this study was to investigate the sites of follistatin and
alpha and beta(A) inhibin mRNA expression in the ovaries of female she
ep fetuses at 90, 100, 120 and 135 days of gestation (term=day 147). A
t 90 and 100 days primordial follicles were formed, followed by the ap
pearance of primary follicles at 100 days of gestation. At days 120 an
d 135, primordial, primary and preantral (i.e. secondary) follicles we
re present in the ovaries, but antral(i.e. tertiary) follicles were no
t observed at any of these gestational ages. Two Booroola genotypes we
re studied: homozygous carriers (BB) and non-carriers (++) of the fecu
ndity gene (FecB). Irrespective of genotype no specific hybridization
of the alpha and beta(A) inhibin riboprobes was detected in any ovaria
n cells at days 90, 100, 120 or 135 of gestation. In control mature ov
aries, on the other hand, strong hybridization in the granulosa cells
of antral follicles was observed. In contrast to alpha and beta(A) inh
ibin, follistatin antisense (but not sense) riboprobes hybridized spec
ifically to the granulosa cells of preantral follicles with two or mor
e layers of cells at days 120 and 135 of gestation. Moreover, hybridiz
ation was also evident in the cells of the ovarian rete at days 120 an
d 135, but not at 90 or 100 days. No follistatin mRNA expression was o
bserved in the granulosa cells of primordial or primary follicles or i
n any other ovarian cell type at any of the gestational ages examined.
No FecB-specific differences in follistatin expression were noted wit
h respect to stage of preantral follicular development and there were
no obvious differences in the intensity of expression. These results s
how that follistatin mRNA is expressed specifically in the granulosa c
ells and intraovarian rete. Expression of follistatin in rete cells wa
s coincident with the increasing numbers of growing follicles within t
he fetal ovary, indicating that rete cell function may have a role in
the ontogeny of early follicular growth. Our results suggest that foll
istatin and alpha and beta(A) inhibin may not be important for the ini
tiation of follicle growth in the sheep ovary, since these genes are n
ot expressed during the transformation of a primordial follicle to a p
rimary structure. However, the evidence for follistatin mRNA expressio
n in the ovine fetal ovary implies that this hormone is likely to play
a role during the early stages of follicle growth.