The generation of germline cells is a critical process in the reproduction of multicellular organisms. Studies in animal models have identified a common repertoire of genes that play essential roles in primordial germ cell (PGC) formation. However, comparative studies also indicate that the timing and regulation of this core genetic program vary considerably in different animals, raising the intriguing questions regarding the evolution of PGC developmental mechanisms in metazoans. Cephalochordates (commonly called amphioxus or lancelets) represent one of the invertebrate chordate groups and can provide important information about the evolution of developmental mechanisms in the chordate lineage. In this study, we used genome and transcriptome data to identify germline-related genes in two distantly related cephalochordate species, Branchiostoma floridae and Asymmetron lucayanum. Branchiostoma and Asymmetron diverged more than 120 MYA, and the most conspicuous difference between them is their gonadal morphology. We used important germline developmental genes in several model animals to search the amphioxus genome and transcriptome dataset for conserved homologs. We also annotated the assembled transcriptome data using Gene Ontology (GO) terms to facilitate the discovery of putative genes associated with germ cell development and reproductive functions in amphioxus. We further confirmed the expression of 14 genes in developing oocytes or mature eggs using whole mount in situ hybridization, suggesting their potential functions in amphioxus germ cell development. The results of this global survey provide a useful resource for testing potential functions of candidate germline-related genes in cephalochordates and for investigating differences in gonad developmental mechanisms between Branchiostoma and Asymmetron species.
Keywords: Amphioxus; Development; Evolution; GO annotation; Primordial germ cell; Reproduction.
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