Retinoic acid receptor alpha is required for synchronization of spermatogenic cycles and its absence results in progressive breakdown of the spermatogenic process.

Targeted mutagenesis of the retinoic acid receptor alpha (RAR alpha) gene has revealed its essential role in spermatogenesis. Although cells in all stages of spermatogenesis were detected in RAR alpha(-/-) testes, there was an increase in degenerating pachytene spermatocytes and a temporary developmental arrest in step 8-9 spermatids in the first wave of spermatogenesis, a delay in the onset of the second wave, and a temporary arrest in preleptotene to leptotene spermatocytes in the first, second, and third waves. A striking aspect of the mutant phenotype was the failure of spermatids to align at the tubular lumen at stage VIII. Furthermore, there were missing or decreased numbers of the predicted cell types in tubules, and they exhibited a profound asynchrony of mixed spermatogenic cell types. In vivo bromodeoxyuridine labeling revealed a significant decrease in germ cell proliferation in both juvenile and adult RAR alpha(-/-) testes and confirmed the arrest at step 8-9 spermatids. Retinoid signaling through RAR alpha, thus, appears to be critical for establishment of synchronous progression of spermatogenesis and the subsequent establishment of correct cellular associations. Copyright 2004 Wiley-Liss, Inc.