Maternal genetic effects in Astyanax cavefish development

Area of Science:

• Evolutionary developmental biology
• Genetics
• Ichthyology

Background:

• The role of maternal factors in evolutionary developmental changes is not well understood.
• Cavefish (CF) and surface fish (SF) morphs of Astyanax mexicanus offer a model to study developmental divergence.
• Previous research has not fully elucidated the maternal genetic contributions to CF adaptations.

Purpose of the Study:

• To investigate the role of maternal genetic effects in the development of cavefish (CF) traits.
• To determine if maternal factors influence CF eye degeneration, pigmentation loss, or jaw enhancement.
• To establish Astyanax mexicanus as a model for studying maternal influences on evolutionary development.

Main Methods:

• Reciprocal hybridization between SF and CF Astyanax mexicanus morphs.
• Generation of F1 hybrids by crossing SF eggs with CF sperm (SF × CF) and CF eggs with SF sperm (CF × SF).
• Analysis of embryonic and larval phenotypes, including eye morphology, lens development, and gene expression patterns.
• Quantification of maternal transcripts (pou2f1b, runx2b, axin1, ß-catenin, syntabulin, sonic hedgehog) in unfertilized eggs and early embryos.

Main Results:

• Reciprocal hybridization demonstrated significant maternal genetic effects on CF eye degeneration.
• CF × SF hybrids exhibited degenerate eye phenotypes (retinal ventral reduction, lens displacement, smaller eye/lens, increased apoptosis) resembling CF.
• Maternal transcripts for ventral fate genes (pou2f1b, runx2b, axin1) were elevated in CF eggs, while dorsal fate gene expression was similar between morphs.
• Maternal effects were not supported for CF pigmentation or jaw development phenotypes.
• Maternal transcripts of a sonic hedgehog gene were present in both SF and CF eggs.

Conclusions:

• Cavefish eye degeneration is significantly controlled by maternal factors established during oogenesis.
• Maternal genetic contributions play a crucial role in the evolution of specific developmental pathways, such as eye loss.
• Astyanax mexicanus reciprocal hybridization is a powerful tool for dissecting maternal genetic influences in evolutionary development.