The role of maternal factors in the evolution of development is poorly understood. Here we describe the use of reciprocal hybridization between the surface dwelling (surface fish, SF) and cave dwelling (cavefish, CF) morphs of the teleost Astyanax mexicanus to determine investigate the roles of maternal genetic effects in cavefish development. Reciprocal hybridization, a procedure in which F1 hybrids are generated by fertilizing SF eggs with CF sperm (SF X CF hybrids) and CF eggs with SF sperm (CF X SF hybrids), revealed that the CF degenerative eye phenotype showed maternal genetic effects. The eyes of CF X SF hybrids resembled the degenerate eyes of CF in showing ventral reduction of the retina and corresponding displacement of the lens within the optic cup, a smaller lens and eyeball, more lens apoptosis, a smaller cartilaginous sclera, and lens-specific gene expression characteristics compared to SF X CF hybrids, which showed eye and lens gene expression phenotypes resembling SF. In contrast, reciprocal hybridization failed to support any roles for maternal genetic effects in the CF regressive pigmentation phenotype or in CF constructive changes related to enhanced jaw development. The Astyanax orthologs of mMaternal transcripts encoded by some of thethe pou2f1b, runx2b, and axin1 genes, which are key involved in determining ventral embryonic fates, genes involved in zebrafish dorsoventral patterning were increased in unfertilized CF eggs. In contrast, maternal mRNAs encoded by the ß-catenin and syntabulin genes, which control dorsal embryonic fates, were unchangedwith theshowed similar expression levels in unfertilized SF and CF eggs. This study reveals that CF eye degeneration is controlled by changes in maternal factors produced during oogenesis and introduces A. mexicanus as a model system for studying the role of maternal changes in the evolution of development.
Maternal Genetic Effects in Astyanax Cavefish Development
