R 4331 (OTTO) Retinoic acid, 98%+ Cas no 302-79-4 - used in stem cells. R 4331 (OTTO) Retinoic acid, 98%+ Cas no 302-79-4 - used to study RA signaling of prospermatogonia transition into spermatogonia. R 4331 (OTTO) Retinoic acid, 98%+ Cas no 302-79-4 - used to study epigenetic regulation by RARα (retinoic acid receptor α).