Mutations in laminin alpha 1 result in complex, lens-independent ocular phenotypes in zebrafish

We report phenotypic and genetic analyses of a recessive, larval lethal zebrafish mutant, bal a69 , characterized by severe eye defects and shortened body axis. The bal a69 mutation was mapped to chromosome 24 near the laminin alpha 1 ( lama1) gene. We analyzed the lama1 gene sequence within bal a69 embryos and two allelic mutants, bal arl and bal uw1 . Missense ( bal a69 ), nonsense ( bal arl ), and frameshift ( bal uw1 ) alterations in lama1 were found to underlie the phenotypes. Extended analysis of bal a69 ocular features revealed disrupted lens development with subsequent lens degeneration, focal cornea dysplasia, and hyaloid vasculature defects. Within the neural retina, the ganglion cells showed axonal projection defects and ectopic photoreceptor cells were noted at inner retinal locations. To address whether ocular anomalies were secondary to defects in lens differentiation, bal a69 mutants were compared to embryos in which the lens vesicle was surgically removed. Our analysis suggests that many of the anterior and posterior ocular defects in bal a69 are independent of the lens degeneration. Analysis of components of focal adhesion signaling complexes suggests that reduced focal adhesion kinase activation underlies the anterior segment dysgenesis in lama1 mutants. To assess adult ocular phenotypes associated with lama1 mutations, genetic mosaics were generated by transplanting labeled bal cells into ocular-fated regions of wild-type blastulas. Adult chimeric eyes displayed a range of defects including anterior segment dysgenesis and cataracts. Our analysis provides mechanistic insights into the developmental defects and ocular pathogenesis caused by mutations in laminin subunits.