EXPRESSION OF THE C-KIT GENE IS CRITICAL FOR MIGRATION OF NEONATAL RAT GONOCYTES IN-VITRO

Rat gonocytes migrate to the basement membrane during the first postna tal week, a change in position crucial for their survival. These cells express the c-kif gene from the day of birth through Day 5 in vivo an d develop the ability to migrate in Sertoli cell-gonocyte cocultures. In this study, we asked whether c-kif expression and synthesis of Kit protein are required for pseudopod production by gonocytes in vitro. T o determine whether gonocyte migration in vitro is invariably accompan ied by c-kif expression, we quantified percentages of gonocytes expres sing c-kif with increasing time in vitro and correlated these data wit h pseudopod development by individual cells. We also determined the ef fect of exposure to Kit antibodies on gonocyte migration in vitro, and , conversely, asked whether addition of exogenous stem cell factor (SC F), the Kit ligand, stimulates pseudopod development. We found that 1) increasing numbers of gonocytes express c-kif with increasing time in vitro; 2) once these cells begin migrating in vitro, the appearance o f a pseudopod on a gonocyte is absolutely correlated with kif expressi on by that cell; 3) incubating cocultures with Kit antibodies signific antly reduces the number of cells with pseudopods, without any detecta ble decrease in numbers of gonocytes; and 4) addition of exogenous SCF to cocultures prepared on Day 5 results in a transient but significan t increase in the percentage of gonocytes with pseudopods even though we found that Sertoli cells in the cultures produce endogenous SCF. Th us, our findings provide evidence to support a role for c-kif expressi on by neonatal gonocytes and, presumably, SCF expression by neonatal S ertoli cells in stimulating migration of these germ cells in vitro.