Ian D. Broadbent

The Caenorhabditis elegans p120 catenin homologue, JAC-1, modulates cadherin–catenin function during epidermal morphogenesis

The cadherin–catenin complex is essential for tissue morphogenesis during animal development. In cultured mammalian cells, p120 catenin (p120ctn) is an important regulator of cadherin–catenin complex function. However, information on the role of p120ctn family members in cadherin-dependent events in vivo is limited. We have examined the role of the single Caenorhabditis elegans p120ctn homologue JAC-1 (juxtamembrane domain [JMD]–associated catenin) during epidermal morphogenesis. Similar to other p120ctn family members, JAC-1 binds the JMD of the classical cadherin HMR-1, and GFP-tagged JAC-1 localizes to adherens junctions in an HMR-1–dependent manner. Surprisingly, depleting JAC-1 expression using RNA interference (RNAi) does not result in any obvious defects in embryonic or postembryonic development. However, jac-1(RNAi) does increase the severity and penetrance of morphogenetic defects caused by a hypomorphic mutation in the hmp-1/α-catenin gene. In these hmp-1 mutants, jac-1 depletion causes failure of the embryo to elongate into a worm-like shape, a process that involves contraction of the epidermis. Associated with failed elongation is the detachment of actin bundles from epidermal adherens junctions and failure to maintain cadherin in adherens junctions. These results suggest that JAC-1 acts as a positive modulator of cadherin function in C. elegans.

Antibody-targeted myofibroblast apoptosis reduces fibrosis during sustained liver injury

BACKGROUND/AIMS Myofibroblast apoptosis promotes the resolution of liver fibrosis. However, retaining macrophages may enhance reversal. The effects of specifically stimulating myofibroblast apoptosis in vivo were assessed. METHODS A single chain antibody (C1-3) to an extracellular domain of a myofibroblast membrane protein was injected as a fluorescent- or gliotoxin conjugate into mice with liver fibrosis. RESULTS C1-3 specifically targeted alpha-smooth muscle actin positive liver myofibroblasts within scar regions of the liver in vivo and did not co-localise with liver monocytes/macrophages. Injection of free gliotoxin stimulated a 2-fold increase in non-parenchymal cell apoptosis and depleted liver myofibroblasts by 30% and monocytes/macrophages by 50% but had no effect on fibrosis severity in the sustained injury model employed. In contrast, C1-3-targeted gliotoxin stimulated a 5-fold increase in non-parenchymal cell apoptosis, depleted liver myofibroblasts by 60%, did not affect the number of monocytes/macrophages and significantly reduced fibrosis severity. Fibrosis reduction was associated with increased metalloproteinase-13 levels. CONCLUSIONS These data demonstrate that specific targeting of liver myofibroblast apoptosis is the most effective anti-fibrogenic therapy, supporting a role for liver monocytes and/or macrophages in the promotion of liver fibrosis reduction.

The C. elegans hmr-1 gene can encode a neuronal classic cadherin involved in the regulation of axon fasciculation

Nervous system morphogenesis is characterized by extensive interactions between individual axon growth cones and their cellular environments. Selective cell adhesion is one mechanism by which the growth of an axon can be modulated, and members of the classic cadherin group of cell adhesion molecules have been shown to play a role in this process in both vertebrates and Drosophila. In Drosophila, there are two classic cadherins: one involved primarily in regulating the morphogenesis of epithelia, and the other, DN-cadherin, required almost exclusively in neuronal development. In contrast, C. elegans has a single classic cadherin gene, hmr-1, whose function is required for epithelial morphogenesis. We show here that hmr-1 also encodes a second classic cadherin via a novel mechanism involving an alternative, neuron-specific promoter, coupled with alternative splicing. This novel HMR-1 isoform is very similar to DN-cadherin, and a mutant strain that specifically lacks the function of this isoform displays defects in the fasciculation and outgrowth of a subset of motor neuron processes; a phenotype that resembles loss of DN-cadherin function in Drosophila. These results indicate that Drosophila and C. elegans share a conserved, cadherin-dependent mechanism involved in regulating axonal patterning and fasciculation.