Dynamic chromosome rearrangements of the white-spotted bamboo shark shed light on cartilaginous fish diversification mechanisms

Cartilaginous fishes have a very high phenotypical diversity, a phenomenon for which the mechanisms have been largely unexplored. Here, we report the genome of the white-spotted bamboo shark as the first chromosome-level genome assembly of cartilaginous fish. Using this genome, we illustrated a dynamic chromosome rearrangement process in the bamboo shark, which resulted in the formation of 13 chromosomes, all of which were sparsely distributed with conserved genes and fast-evolving. We found the fast-evolving chromosomes to be enriched in immune-related genes with two chromosomes harboring the major genes for developing the single-chain antibody. We also found chromosome rearrangements to have resulted in the loss of two genes (p2rx3 and p2rx5) which we also showed were involved in cartilage development using a CRISPR/Cas9 approach in zebrafish. Our study highlighted the significance of chromosome rearrangements in the phenotypical evolution of cartilaginous fishes, providing clues to inform further studies on mechanisms for fish diversification.