Cx36 is a target of Beta2/NeuroD1, which associates with prenatal differentiation of insulin-producing ß cells.

The insulin-producing ß cells of pancreatic islets are coupled by connexin36 (Cx36) channels. To investigate what controls the expression of this connexin, we have investigated its pattern during mouse pancreas development, and the influence of three transcription factors that are critical for ß-cell development and differentiation. We show that (1) the Cx36 gene (Gjd2) is activated early in pancreas development and is markedly induced at the time of the surge of the transcription factors that determine ß-cell differentiation; (2) the cognate protein is detected about a week later and is selectively expressed by ß cells throughout the prenatal development of mouse pancreas; (3) a 2-kbp fragment of the Gjd2 promoter, which contains three E boxes for the binding of the bHLH factor Beta2/NeuroD1, ensures the expression of Cx36 by ß cells; and (4) Beta2/NeuroD1 binds to these E boxes and, in the presence of the E47 ubiquitous cofactor, transactivates the Gjd2 promoter. The data identify Cx36 as a novel early marker of ß cells and as a target of Beta2/NeuroD1, which is essential for ß-cell development and differentiation.

Antisense genes to induce exon inclusion.

Many inherited diseases are associated with changed splicing patterns, and alternative splicing influences several biological processes as well as the replication of certain viral pathogens. For this reason, there is a broad interest in modulating individual splicing events for therapeutic purposes. Based on the small nuclear RNA (snRNA) U7, we have developed expression vectors for short antisense RNAs that accumulate in the cell nucleus where splicing occurs and that can very specifically modulate the splicing of individual exons. More specifically, in the context of the fatal neuromuscular disorder Spinal Muscular Atrophy (SMA), we have shown that U7 snRNA constructs can restore the inclusion of exon 7 in the SMN2 gene and thereby alleviate or even fully cure disease symptoms in a severe mouse model for SMA. Here we describe more generally procedures to produce U7 constructs to induce exon inclusion and to test their efficiency in cell culture experiments at the level of RNA as well as protein. The analytical methods comprise reverse transcription (RT-)PCR to detect the splicing changes, quantitative real-time RT-PCR to measure U7 snRNA expression levels and western blot and immunofluorescence methods to detect a restoration of protein expression. Additionally, we indicate how U7 cassettes can be introduced into gene transfer vectors for in vivo experiments in animal models or to transduce cell systems that are not readily amenable to DNA transfection.

Connexin36 and pancreatic beta-cell functions.

Most cell types are functionally coupled by connexin (Cx) channels, i.e. exchange cytoplasmic ions and small metabolites through gap junction domains of their membrane. This form of direct cell-to-cell communication occurs in all existing animals, whatever their position in the phylogenetic scale, and up to humans. Pancreatic beta-cells are no exception, and normally cross-talk with their neighbors via channels made of Cx36. These exchanges importantly contribute to coordinate and synchronize the function of individual cells within pancreatic islets, particularly in the context of glucose-induced insulin secretion. Compelling evidence now indicates that Cx36-mediated coupling, and/or the Cx36 protein per se, play significant regulatory roles in various beta-cell functions, ranging from the biosynthesis, storage and release of insulin. Recent preliminary data further suggest that the protein may also be implicated in the balance of beta-cell growth versus necrosis and apoptosis, and in the regulated expression of specific genes. Here, we review this evidence, discuss the possible involvement of Cx36 in the pathophysiology of diabetes, and evaluate the relevance of this connexin in the therapeutic approaches to the disease.