Ja. Parrott et Mk. Skinner, DIRECT ACTIONS OF KIT-LIGAND ON THECA CELL-GROWTH AND DIFFERENTIATIONDURING FOLLICLE DEVELOPMENT, Endocrinology, 138(9), 1997, pp. 3819-3827
The direct actions of kit-ligand/stem cell factor (KL) in developing o
varian follicles were investigated. Previous studies have shown that g
ranulosa cells express KL that can support oocyte development. The cur
rent study demonstrates that KL can also act directly on theca cells t
o promote cellular growth and differentiation. Through RT-PCR analysis
it was shown that bovine granulosa cells express KL, and theca cells
express the receptor c-kit. Bovine theca interna cells were isolated a
nd cultured in serum-free conditions to study KZ actions. KL stimulate
d theca cell growth in a dose-dependent manner as measured by [H-3]thy
midine incorporation into DNA when cells were cultured under subconflu
ent conditions. KL had no effect on theca cell androstenedione or prog
esterone production under these growth-permissive conditions. In contr
ast, KL stimulated theca cell androstenedione production but had no ef
fect on progesterone production when theca cells were cultured under c
onfluent (non-growth-permissive) conditions. Estradiol (10(-7) M) and
human CG (100 ng/ml) were used as controls and regulated theca cell st
eroid production at any cell density. These results demonstrate that K
L can directly stimulate theca cell growth and steroid production duri
ng follicular development. The observation that KL stimulated androste
nedione production but not progesterone production suggests that KL pr
omotes a follicular phase differentiated state in theca cells. The pot
ential reg ulation of KL and c-kit expression during follicular develo
pment was studied using a specific quantitative RT-PCR procedure. Tota
l RNA from granulosa cells (for KL) and theca cells (for c-kit) was ex
amined from small (<5 mm), medium (5-10 mm), and large (>10 mm) size f
ollicles. Steady state levels of KL messenger RNA were highest in gran
ulosa cells from large size follicles and lowest in small and medium s
ize follicles. No differences were observed in the steady state levels
of c-bit messenger RNA in theca cells from small, medium, or large si
ze follicles. The observation that KL expression is highest in large s
ize follicles suggests that KL may be important for increased growth a
nd steroid production in large and dominant follicles. Observations de
monstrate that KL can dramatically alter theca cell function and suppo
rt the hypothesis that local granulosa-theca cell interactions play an
important role in regulating cellular function within ovarian follicl
es. This study identifies KL as the first granulosa cell-derived growt
h factor that can directly stimulate theca cell growth and androstened
ione production in the absence of gonadotropins.