Breaking symmetry on time

Distinct mechanisms determine organ left-right asymmetry patterning in an uncoupled way

Disruption of Nodal in the lateral plate mesoderm (LPM) usually leads to left-right (LR) patterning defects in multiple organs. However, whether the LR patterning of organs is always regulated in a coupled way has largely not yet been elucidated. In addition, whether other crucial regulators exist in the LPM that coordinate with Nodal in regulating organ LR patterning is also undetermined. In this paper, after briefly summarizing the common process of LR patterning, the most puzzling question regarding the initiation of asymmetry is considered and the divergent mechanisms underlying the uncoupled LR patterning in different organs are discussed. On the basis of cases in which different organ LR patterning is determined in an uncoupled way via an independent mechanism or at a different time, we propose that there are other critical factors in the LPM that coordinate with Nodal to regulate heart LR asymmetry patterning during early LR patterning.

Genomic organization, expression, and phylogenetic analysis of Ca2+ channel beta4 genes in 13 vertebrate species

The Ca(2+) channel beta-subunits, encoded by CACNB genes 1-4, are membrane-associated guanylate kinase (MAGUK) proteins. As auxiliary subunits of voltage-gated Ca(2+) channels, the beta-subunits facilitate membrane trafficking of the pore-forming alpha1 subunits and regulate voltage-dependent channel gating. In this report, we investigate whether two zebrafish beta4 genes, beta4.1 and beta4.2, have diverged in structure and function over time. Comparative expression analyses indicated that beta4.1 and beta4.2 were expressed in separable domains within the developing brain and other tissues. Alternative splicing in both genes was subject to differential temporal and spatial regulation, with some organs expressing different subsets of beta4.1 and beta4.2 transcript variants. We used several genomic tools to identify and compare predicted cDNAs for eight teleost and five tetrapod beta4 genes. Teleost species had either one or two beta4 paralogs, whereas each tetrapod species contained only one. Teleost beta4.1 and beta4.2 genes had regions of sequence divergence, but compared with tetrapod beta4s, they exhibited similar exon/intron structure, strong conservation of residues involved in alpha1 subunit binding, and similar 5' alternative splicing. Phylogenetic results are consistent with the duplicate teleost beta4 genes resulting from the teleost whole genome duplication. Following duplication, the beta4.1 genes have evolved faster than beta4.2 genes. We identified disproportionately large second and third introns in several beta4 genes, which we propose may provide regulatory elements contributing to their differential tissue expression. In sum, both mRNA expression data and phylogenetic analysis support the evolutionary divergence of beta4.1 and beta4.2 subunit function.