POU4F2 and Infertility: These ultrastructural abnormalities in Brn-3b KO sperm, which include acrosomal defects, disorganization of the mitochondrial and fibrous sheath aligns with observation of infertility in Brn-3b KO male mice and may also explain our observation of reduced sperm count and poor motility in Brn-3b KO sperm.