The in vivo form of the murine class VI POU protein Emb is larger than that encoded by previously described transcripts

pouC Regulates Expression of bmp4 During Atrioventricular Canal Formation in Zebrafish

BACKGROUND

Many human gene mutations have been linked to congenital heart disease (CHD), yet CHD remains a major health issue worldwide due in part to an incomplete understanding of the molecular basis for cardiac malformation.

RESULTS

Here we identify the orthologous mouse Pou6f1 and zebrafish pouC as POU homeodomain transcription factors enriched in the developing heart. We find that pouC is a multi-functional transcriptional regulator containing separable activation, repression, protein-protein interaction, and DNA binding domains. Using zebrafish heart development as a model system, we demonstrate that pouC knockdown impairs cardiac morphogenesis and affects cardiovascular function. We also find that levels of pouC expression must be fine-tuned to enable proper heart formation. At the cellular level, we demonstrate that pouC knockdown disrupts atrioventricular canal (AVC) cardiomyocyte maintenance, although chamber myocyte specification remains intact. Mechanistically, we show that pouC binds a bmp4 intronic regulatory element to mediate transcriptional activation.

CONCLUSIONS

Taken together, our study establishes pouC as a novel transcriptional input into the regulatory hierarchy that drives AVC morphogenesis in zebrafish. We anticipate that these findings will inform future efforts to explore functional conservation in mammals and potential association with atrioventricular septal defects in humans. Developmental Dynamics 248:173-188, 2019. © 2018 Wiley Periodicals, Inc.

Involvement of mPOU (Brn-5), a class VI POU protein, in the gene expression of Pit-1 as well as PRL

PRL is mainly expressed in the pituitary and its gene expression is regulated by a variety of transcription factors including Pit-1. Brn-5 is a transcription factor that binds to Pit-1 binding elements and stimulates PRL reporter gene expression. In this study, the role of Brn-5 was examined. RNA interference (RNAi) against Brn-5 leaded to reduction in PRL content of GH3 cells, indicating endogenous Brn-5 may play a role in PRL gene expression. Furthermore Brn-5 RNAi decreased Pit-1 mRNA. Transfection of expression vectors for mPOU (human ortholog of Brn-5) modestly but significantly stimulated activities of PRL-Luc and Pit-1-Luc reporter genes in GH3 and HEK 293 cells. In addition, mPOU showed synergistic action with Pit-1 and CBP on PRL-Luc expression. mPOU-FL, a splicing variant of mPOU, showed weaker activity than mPOU. Chip assay suggested binding of mPOU to PRL and Pit-1 promoters of genomic DNA. Taken together, these results suggest that mPOU (Brn-5) enhances PRL gene expression directly in association with Pit-1 and CBP, and indirectly via the activation of Pit-1 gene expression.

A novel complex regulates cardiac actin gene expression through interaction of Emb, a class VI POU domain protein, MEF2D, and the histone transacetylase p300

Expression of the mouse cardiac actin gene depends on a distal enhancer (-7 kbp) which has been shown, in transgenic mice, to direct expression to embryonic skeletal muscle. The presence of this distal sequence is also associated with reproducible expression of cardiac actin transgenes. In differentiated skeletal muscle cells, activity of the enhancer is driven by an E box, binding MyoD family members, and by a 3' AT-rich sequence which is in the location of a DNase I-hypersensitive site. This sequence does not bind MEF2 proteins, or other known muscle transcription factors, directly. Oct1 and Emb, a class VI POU domain protein, bind to consensus sites on the DNA, and it is the binding of Emb which is important for activity. Emb binds as a major complex with MEF2D and the histone transacetylase p300. The form of Emb present in this complex and as a major form in muscle cell extracts is longer (80 kDa) than that previously described. These results demonstrate the importance of this novel complex in the transcriptional regulation of the cardiac actin gene and suggest a potential role in chromatin remodeling associated with muscle gene activation.