Abstract
Cartilaginous fishes (chondrichthyans) are comprised of sharks, rays and chimaeras, and they generally exhibit internal fertilization, low fecundity, long gestation time, and enhanced longevity. Although collectively known as ‘fishes’, these life history traits do not resemble the counterparts well studied in teleost fishes and remain largely unexplored at the molecular level. We launched the Squalomix consortium (https://github.com/Squalomix/info) to conduct evolutionary genomic analysis of sharks and rays (Nishimura, et al. F1000Res 2022) and have reported a conserved nature of their genomes. This conserved nature is reflected in well-retained repertoires orthologous to the genes encoding endocrine hormones and their receptors responsible for reproduction and other physiological processes in mammals (Hara, et al., Nat Ecol Evol 2018). We have also investigated a genomic manifestation of reproductive systems of chondrichthyans, especially in the organization of sex chromosomes. Anecdotally, no natural and experimental case reports of sex reversal implied firmly established sex chromosome and sex determination systems of chondrichthyans. Our original effort enabled by cultured cells as well as existing reports have revealed XY or XO systems in some shark and ray species (summarized in Uno, et al., Comm Biol 2020). Among them, our analysis of Stegostoma tigrinum, the zebra shark (or leopard shark), revealed a putative X chromosome, allowing the probable first-ever DNA-based characterization of a chondrichthyan sex chromosome. Our comparative study covering different fish lineages permits molecular evolutionary exploration of reproductive mechanisms in vertebrates and how their components have been harboured in the chondrichthyan genomes.
About Prof. Shigehiro Kuraku
Shigehiro leads the Laboratory for Phyloinformatics at the RIKEN Centre for Biosystems Dynamics Research. His research uses cutting-edge DNA sequencing technologies and bioinformatics to explore the diversity and evolution of vertebrate genomes and epigenomes. His lab is involved in whole genome sequencing and analysis projects, fostering biodiversity literacy from a genomics and molecular viewpoint.
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