Vitamin A-deficient testis germ cells are arrested at the end of S phase of the cell cycle: a molecular study of the origin of synchronous spermatogenesis in regenerated seminiferous tubules.

Vitamin A deficiency in male rats arrests spermatogenesis and leads to the loss of advanced germ cells. Retinol treatment of these rats seems to result in a synchronous spermatogenesis initiated from the remaining type A1 spermatogonia. To determine at a molecular level the onset of the M phase of the cell cycle occurring in the retinol-treated germ cells, the H1 histone kinase activity associated with the cdc2 kinase/cyclin B complex was measured. This kinase activity is an excellent molecular indicator of mitosis (M phase) since it is known to be high only for approximately 2 h between the G2/M phase transition of the cell cycle and the metaphase of mitosis. This activity was low in vitamin A-deficient testis, increased by 4 h after retinol treatment, and reached a 15.6-fold level at 12 h. These results suggest that the germ cells of vitamin A-deficient testis begin to enter the M phase around 4 h after retinol injection, with the highest percentage of cells entering at 12 h. These results are consistent with placing the origin of synchronous spermatogenesis in regenerated seminiferous tubules at the end of the S phase of the cell cycle.