Sexual and asexual development: two distinct programs producing the same tunicate.

Colonial tunicates are the only chordate that possess two distinct developmental pathways to produce an adult body: either sexually through embryogenesis or asexually through a stem cell-mediated renewal termed blastogenesis. Using the colonial tunicate Botryllus schlosseri , we combine transcriptomics and microscopy to build an atlas of the molecular and morphological signatures at each developmental stage for both pathways. The general molecular profiles of these processes are largely distinct. However, the relative timing of organogenesis and ordering of tissue-specific gene expression are conserved. By comparing the developmental pathways of B. schlosseri with other chordates, we identify hundreds of putative transcription factors with conserved temporal expression. Our findings demonstrate that convergent morphology need not imply convergent molecular mechanisms but that it showcases the importance that tissue-specific stem cells and transcription factors play in producing the same mature body through different pathways. • Embryogenesis and blastogenesis have different morphological and molecular programs • Distinct molecular programs can lead to the same outcome • Tissue-specific transcriptional timings are shared in both developmental pathways • The expression and timing of many transcription factors are conserved in development Kowarsky et al. present a developmental atlas of colonial tunicates. They show how sexual and asexual reproduction processes, despite having largely distinct molecular programs, share similar timing of organ formation. Tissue-specific stem cells and transcription factors display similar genetic dynamics in different developmental pathways to produce the same organism. [ABSTRACT FROM AUTHOR]