Interaction of Hand2 and E2a is important for transcription of Phox2b in sympathetic nervous system neuron differentiation.

Transcription factors play a crucial role in the development of various tissues. In particular, the transcription factors of the basic helix-loop-helix (bHLH) family are crucial regulators of neurodifferentiation. Previous studies suggested that the bHLH transcription factor Hand2 is essential for sympathetic nervous system neuron differentiation in vivo, but the molecular mechanisms involved have not been well elucidated. It is important for understanding their mode of action in cellular differentiation to clarify how these bHLH factors regulate distinct transcriptional targets in a temporally and spatially controlled manner. Recent reports on ES cell differentiation suggested that its molecular mechanism mimics that of in vivo neurogenesis. However, the diverse nature of ES cell populations has prevented efficient analysis. To address this issue, we previously established a cell line in P19 embryonal carcinoma (EC) cells. Efficient sympathetic nervous system (SNS) neuron differentiation is induced in the cell line. Using this cell line, we succeeded in showing that the interaction of bHLH transcription factor Hand2 with E2a is required for transcription of Phox2b, which is essential for autonomic nervous system neuron development, and this binding activates this expression in SNS differentiation. Moreover, we also demonstrated that Hes5 regulated the transcription of Phox2b as a negative regulator and it inhibited the SNS differentiation. These findings have enabled us to determine the novel regulatory mechanism of Phox2b in SNS differentiation.

The bHLH transcription factor Hand2 regulates the expression of nanog in ANS differentiation.

The basic helix-loop-helix transcription factor Hand2 is induced by bone morphogenetic proteins (BMPs) in neural crest-derived precursor cells during the early stage of development of the autonomic nervous system (ANS). Previous studies showed that Hand2 was essential for the ANS differentiation. However, regulatory mechanism of pluripotent genes has not been elucidated in ANS differentiation. Here, we show that Hand2 regulated nanog expression in ANS differentiation. Our studies demonstrated that the forced expression of Hand2 promoted the ANS differentiation program in P19 embryonal carcinoma (EC) cells without aggregation. Furthermore, our results suggested that Hand2 bound to the promoter of nanog, a gene required for embryonic stem cells self-renewal, and suppressed nanog expression after Hand2 induction. The rapid downregulation of nanog mRNA during ANS differentiation correlated with the Hand2 transcriptional activity and nanog promoter methylation. These findings are evidence for a presence of the novel regulatory mechanism of nanog in ANS differentiation.

Expression and functional significance of mouse paraspeckle protein 1 on spermatogenesis.

Paraspeckle protein 1 (PSP1) in humans is a recently identified component protein of a novel nuclear body, paraspeckle. The protein has a DBHS (Drosophila behavior, human splicing) motif that is found in PSF and p54(nrb)/NonO proteins. These DBHS-containing proteins have been reported to be involved in various nuclear events such as DNA replication, transcription, and mRNA processing. Here we show that mouse paraspeckle protein 1 (mPSP1; encoded by the Pspc1 gene) has two isoforms with different C-termini lengths. Abundant expression of the longer isoform (mPSP1-alpha) and the shorter one (mPSP1-beta) were observed in testis and kidney, respectively. Transiently expressed mPSP1-alpha was localized in nuclei, but mPSP1-beta was localized in both nuclei and cytoplasm. These observations suggest that alternative splicing regulates tissue distribution and subcellular localization. Like other DBHS-containing proteins, mPSP1 has RNA-binding activity. In mouse testis, mPSP1-alpha was found in the nuclear matrix fraction. Furthermore, by coimmunoprecipitation, we confirmed that mPSP1 interacts with other DBHS-containing proteins, PSF and p54(nrb)/NonO. Therefore, we conclude that mPSP1 may regulate multiple phases of important nuclear events during spermatogenesis.

CPEB2, a novel putative translational regulator in mouse haploid germ cells.

Translational control of specific mRNAs by cytoplasmic polyadenylation has fundamental roles in gametogenesis. The cytoplasmic polyadenylation element binding (CPEB) protein regulates cytoplasmic polyadenylation of mRNAs as a trans factor in oogenesis and spermatogenesis. The CPEB protein contains two RNA recognition motifs and a Zn-finger structure. Proteins (KIAA0940 and KIAA1673) with similar structures are predicted from the genome database, but nothing is known about their expression and function. Here, we report another novel member of the CPEB protein family, CPEB2. Comparison of the amino acid sequences of CPEB family members suggests that the family can be divided structurally and, perhaps, functionally into two groups: the CPEB group, and the CPEB2-KIAA0940-KIAA1673 group. The CPEB2 maps to mouse chromosome distal 5B and is abundantly expressed in testis. However, it was detected by reverse transcription-polymerase chain reaction in all tissues that we examined. It preferentially binds to poly(U) and localizes to the cytoplasm in transfected HeLa cells. The CPEB2 is expressed postmeiotically in mouse spermatogenesis, suggesting a possible role in translational regulation of stored mRNAs in transcriptionally inactive haploid spermatids.