Appearance of cysts of round spermatids ran about 6 h earlier in both lut and rbp4 mutants compared with wild-type testes, as about one-third of testes from those two mutant genotypes contained at least one cyst with round spermatids at 104-106 h PHS (versus 110-112 h PHS in wild type). This evidence concerns the gene RBP4 and cyst.