Activin A selectively represses expression of the membrane-bound isoform of Kit ligand in human fetal ovary.

Germ cell-expressed activin A promotes germ cell survival and proliferation indirectly, possibly by maintaining ovarian pregranulosa cells in an undifferentiated state and preventing primordial follicle formation until oocytes have matured sufficiently. We have previously demonstrated that recombinant activin A can repress the expression of Kit ligand (KITLG) in cultures of human fetal ovaries, and here we extend this finding to show that this repression acts selectively on the membrane-bound isoform of Kit ligand without affecting the soluble form, providing a potential mechanism for suppressing direct interaction between somatic and germ cells and thus inhibiting precocious primordial follicle formation.