FIG. 4.

Schematic representation of the secretion of testosterone by fetal and adult Leydig cells during gestation, postnatally, and in the adult. The switch over from fetal- to adult-type Leydig cells occurs prepubertally, starting around Day 7. LuRKO males are hypoandrogenic from this point forward due to a failure to develop adult Leydig cells. Lower panels show transcriptional data for selected fetal/adult Leydig cell antigens during the period. The dotted arrows in these panels indicate the effect of 48 h of testosterone treatment at a dose of 2.5 mg.