The testis-specific cytoplasmic poly(A) polymerase PAPOLB/TPAP is essential for spermatogenesis. Although this enzyme is responsible for poly(A) tail extension of a subset of mRNAs in round spermatids, the stability and translational efficiency of these mRNAs are unaffected by the absence of PAPOLB. To clarify the functional importance of this enzyme’s adenylation activity, we produced PAPOLB-null mice expressing a polyadenylation-defective PAPOLB mutant (PAPOLBD114A), in which the catalytic Asp at residue 114 was mutated to Ala. Introducing PAPOLBD114A failed to rescue PAPOLB-null phenotypes, such as reduced expression of haploid-specific mRNAs, spermiogenesis arrest, and male infertility. These results suggest that PAPOLB regulates spermatogenesis through its adenylation activity.

Mouse testes contain several isoforms of cytoplasmic poly(A)-binding proteins (PABPCs), including ubiquitous PABPC1 and testis-specific PABPC2/PABPt. PABPC2 is characterized by its absence from translationally active polyribosomes and elongating spermatids. To elucidate the function of PABPC2 in spermatogenesis, we produced mutant mice lacking PABPC2. The PABPC2-null mice showed normal fertility. The processes of spermatogenesis and sperm migration in the testes and epididymides, respectively, were normal in the mutant mice. When the involvement of PABPC2 in translational regulation of haploid-specific mRNAs was examined, these mRNAs were correctly transcribed in round spermatids and translated in elongating spermatids. Moreover, immunoblot analysis revealed low abundance of PABPC2 relative to PABPC1 in spermatogenic cells. These results suggest that PABPC2 may be either functionally redundant with other PABPCs (including PABPC1) or largely dispensable for translational regulation during spermiogenesis.