Molecular mechanism of spermatogenesis regulated by a testis-specific poly(A) polymerase, TPAP

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To elucidate the molecular mechanism of spermatogenesis, I have examined the implication of a testis-specific poly(A) polymerase, TPAP, in mouse spermatogenesis. The following experimental results have been obtained :1.Transgenic mice overexpressing TPAP exhibited normal spermatogenesis and fertility. The sizes of some transcription factor mRNAs as the substrates of TPAP were also unaffected, implying the presence of a regulatory mechanism(s) defining the extent of the cytoplasmic mRNA polyadenylation.2.TPAP was capable of interacting with mRNAs encoding germ cell morphogenesis-regulating proteins and transcription factors, including protamine, TFIIAγ, and CREMτ. These data suggest that TPAP presumably has the selectivity for mRNA recognition.3.Cytoplasmic polyadenylation element-binding protein 2, CPEB2, was expressed in the testis and was capable of binding to the 3'-untranslated regions of TFIIAγ and TRF2 mRNAs, thus implying a possible implication of CPEB2 in the poly(A) elongation of mRNAs, in cooperation with TPAP.4.Poly(A) binding protein PABPC1 was capable of binding to the 3'-untranslated region of TFIIAγ mRNA only when the mRNA contained poly(A) tail. Since TPAP showed the inability to bind to the same mRNA with and without the poly(A) tail, TPAP may interact with the TFIIAγ mRNA possibly through a protein complex.5.RecQL exhibiting a helicase activity has been identified as one of the TPAP-interacting proteins. Indeed, TPAP showed a direct binding activity to RecQL.