Authors

D Huchon¹;  ¹ Tel Aviv University, Israel

Discussion

Myxozoa are a diverse and enigmatic group of microscopic parasitic animals closely related to jellyfish and hydroids. Evolutionary research on Myxozoa has long been hampered by their small size and lack of informative morphological characteristics. The challenges extended to DNA sequencing, where issues such as obtaining substantial DNA quantities, fast evolutionary rates, and host contaminations presented hurdles. This lecture explores how high-throughput sequencing methodologies provided novel insights into myxozoan evolution and genomics. Leveraging genomic data, we could conclusively confirme the phylogenetic positioning of myxozoans as the sister clade of Polypodium hydriforme. We revealed that myxozoans have a small nuclear genome, characterized by an exceptionally fast evolutionary rate. Intriguingly, all myxozoans have lost crucial animal genomic and developmental pathways, including cytosine methylation and all Hox genes. Moreover, our investigations have brought to light the fascinating case of Henneguya salminicola, a myxozoan species that has lost aerobic respiration, marking the first molecular characterization of an anaerobic animal. In contrast to the compact nuclear genome, myxozoans feature colossal mitochondrial genomes, which contain many non-coding regions comprised of repetitive elements. Few myxozoan species harbor a partitioned mitochondrial genome organized into several mega-chromosomes. Most canonical genes commonly found in all metazoan mitochondrial genomes are absent in myxozoans, likely due to their accelerated evolutionary rate. Conversely, numerous open reading frames with unknown functions have been identified. While comparative genomics and transcriptomics of myxozoan species remain challenging due to their rapid evolutionary rate and the subsequent complexities in reliable genomic annotation, future genomic data are expected to revolutionize our understanding of myxozoan host relationships, evolution, and ecology.