Desmin enters the nucleus of cardiac stem cells and modulates Nkx2.5 expression by participating in transcription factor complexes that interact with the nkx2.5 gene.

The transcription factor Nkx2.5 and the intermediate filament protein desmin are simultaneously expressed in cardiac progenitor cells during commitment of primitive mesoderm to the cardiomyogenic lineage. Up-regulation of Nkx2.5 expression by desmin suggests that desmin may contribute to cardiogenic commitment and myocardial differentiation by directly influencing the transcription of the nkx2.5 gene in cardiac progenitor cells. Here, we demonstrate that desmin activates transcription of nkx2.5 reporter genes, rescues nkx2.5 haploinsufficiency in cardiac progenitor cells, and is responsible for the proper expression of Nkx2.5 in adult cardiac side population stem cells. These effects are consistent with the temporary presence of desmin in the nuclei of differentiating cardiac progenitor cells and its physical interaction with transcription factor complexes bound to the enhancer and promoter elements of the nkx2.5 gene. These findings introduce desmin as a newly discovered and unexpected player in the regulatory network guiding cardiomyogenesis in cardiac stem cells.

Duplication of the caspase-12 prodomain and inactivation of NLRC4/IPAF in the dog.

Caspases-1, 4, 5, and 12 and other proteins containing caspase recruitment domains (CARDs) play crucial roles in the induction of inflammatory processes. Recently, hybrid caspase-1/4 mRNAs encoding proteases with two CARDs were identified in cat and dog, indicating that the molecular machinery of caspase-dependent inflammation has an unconventional composition in members of the order Carnivora. Here we extended these studies and identified, both in cat and dog, splice variants of caspase-12, which also contained two CARDs. Comparative genomics analysis of the repertoire of canine CARD proteins revealed that the gene encoding NLRC4/IPAF, which is implicated in the inflammatory response to cytosolic flagellin, was inactivated by deleterious mutations in the dog. Our results demonstrate that the repertoires of CARD proteins in cat and dog differ significantly from that of humans and suggest the existence of uncharacterized pathways of inflammasome-mediated signaling in Carnivora.

Identification of a novel exon encoding the amino-terminus of the predominant caspase-5 variants.

Caspase-5 is a caspase-1-like protease with pro-apoptotic and pro-inflammatory activities. Here we have identified a novel exon at the 5'-end of the human caspase-5 gene. This novel exon was present in six alternatively spliced caspase-5 mRNA variants expressed in human peripheral blood mononuclear cells (PBMC) and encoded the previously unknown amino-terminus of caspase-5. The genomic region upstream of this exon contained sequence elements homologous to those of the caspase-11 promoter in the mouse, and transcription of caspase-5 was upregulated by lipopolysaccharide (LPS) in a caspase-11-like manner in human PBMC in vivo. Taken together, our findings call for a revision of the structure of caspase-5 at the genomic level as well as at the mRNA and protein levels.