XCL-2 is a novel m-type calpain and disrupts morphogenetic movements during embryogenesis in Xenopus laevis

We identified a novel cDNA, XCL-2, encoding an m-type calpain, a calcium-dependent intracellular protease. This protein has all characteristic structures and active sites of canonical calpains. Zygotic transcription of the gene was first detected at stage 10. It is expressed exclusively in the ventral circumblastoporal collar and the mesoderm-free zone at the most anterior tip of neural fold in late gastrulae and neurulae. In later stages, expression is only found in cement gland and proctodeum. It is also expressed in a tissue-specific manner. In adult tissues, various levels of expression were detected in brain, eye, heart, intestine, kidney, lung, stomach and testis, but not in liver, muscle, nerve, ovary, skin and spleen. Overexpression of wild-type XCL-2 suggests that this gene is involved in gastrulation movement and convergent extension during gastrulation and neurulation. Overexpression of a dominant-negative mutant caused a phenotype morphologically similar to, but histologically different from, that caused by overexpression of wild-type XCL-2. The mutant phenotype can be rescued by injection of wild-type XCL-2. These data suggest that XCL-2 plays an important role in convergent extension movements during embryogenesis in Xenopus laevis.