Structural Analysis and Spatiotemporal Expression of Atxn1 Genes in Zebrafish Embryos and Larvae

Zebrafish have come into focus to model cerebellar diseases such as spinocerebellar ataxias (SCAs), which is caused by an expansion of translated CAG repeats in several unrelated genes. In spinocerebellar ataxia type 1 (SCA1), gain-of-function in the mutant ATXN1 contributes to SCA1's neuropathy. Human ATXN1 and its paralog ATXN1L are chromatin-binding factors, act as transcriptional repressors, and have similar expression patterns. However, little is known about atxn1 genes in zebrafish. Recently, two family members, atxn1a and atxn1b, were identified as duplicate orthologs of ATXN1, as was atxn1l, the ortholog of ATXN1L. In this study, we analyzed the phylogenetic relationship of the atxn1 family members in zebrafish, compared their genetic structures, and verified the predicted transcripts by both RT-PCR and whole-mount in situ hybridization. All three genes, atxn1a, atxn1b, and atxn1l, show overlapping, but also distinct, expression domains during embryonic and larval development. While atxn1a and atxn1l display similar spatiotemporal embryonic expression, atxn1b expression is initiated during the onset of brain development and is predominantly expressed in the cerebellum throughout zebrafish development. These results provide new insights into atxn1 genes and their expression patterns in zebrafish during embryonic and late-larval development and may contribute importantly to future experiments in disease modeling of SCAs.