Coleoid cephalopods have distinctive neural and morphological characteristics compared to the other invertebrates. Early studies reported massive genomic rearrangements occurred before the split of octopus and squid l...
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Coleoid cephalopods have distinctive neural and morphological characteristics compared to the other invertebrates. Early studies reported massive genomic rearrangements occurred before the split of octopus and squid lineages, which might be related to the neural innovations of their brain, yet the details remain elusive. Here we combine genomic and single-cell transcriptome analyses to investigate the octopod chromosome evolution and cerebral characteristics. We present a chromosome-level genome assembly of a golden-ringed octopus, Amphioctopus fangsiao, and a single-cell transcriptome of its supra-esophageal brain. Chromosome-level synteny analyses estimate that the chromosomes of the ancestral octopods experienced multiple chromosome fission/fusion and loss/gain events by comparing with the nautilus genome as outgroup, and that a conserved genome organization was detected during the evolution process from the last common octopod ancestor to their descendants. Besides, protocadherin, GPCR and C2H2 ZNF genes are thought to be highly related to the neural innovations in cephalopods, and the chromosome analyses find several collinear modes of these genes on the octopod chromosomes, such as the collinearity between PCDH and C2H2 ZNF, as well as between GPCR and C2H2 ZNF. Phylogenetic analyses show that the expansion of the octopod protocadherin genes is drove by a tandemduplication mechanism on one single chromosome, including two separate expansions at 65 Ma and 8-14 Ma, respectively. Furthermore, we identify eight cell-types(i.e., cholinergic and glutamatergic neurons) in the supra-esophageal brain of A. fangsiao, and the single-cell expression analyses revealthe co-expression of protocadherin and GPCR in specific neural cells, which may contribute to the neural development and signal transductions in the octopod brain. The octopod genome analyses reveal the dynamic evolutionary history of octopod chromosomes and neural-related gene families. The single-cell transcri
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