Ascidiella aspersa belongs to ascidians, which are the class of chordates, the closest relatives of vertebrates. It is a potential model organism for bio-imaging study due to its extremely transparent embryos (Shito et al., 2020) as well as is a globally distributed cosmopolitan species.However, there are no standard developmental tables for this organism. In this study, as a first step to establish A. aspersa as a model organism, we have provided a standard developmental table with web-based digital image resource.

It contains three-dimensional (3D) images of A. aspersa embryos and cross-sectional images through the developmental time course. These 3D images were reconstructed from more than 3,000 high-resolution images by confocal laser scanning microscopy. With reference to the standardized developmental table of the Ciona intestinalis type A (Hotta et al., 2007), 26 different developmental stages (stages 1-26) from fertilized eggs to hatched larvae were customized for A. aspersa. We annotated the cell lineages up to the cleavage period and compared the cleavage patterns, the embryonic morphology and developmental time with that of C. intestinalis. We found that the stereo-typed cleavage patterns and developmental time up to the neurula period as the C. intestinalis was conserved also in A. aspersa. On the other hand, the ratio of the trunk and tail length in tailbud period was smaller than that of C. intestinalis, and the timing of the bending of the tail is relatively earlier than that of C. intestinalis.

This A. aspersa standard 3D digital resource is essential for connecting different omics data to different spatiotemporal hierarchies, and it is useful for system-level understanding of chordate development.

Please refer to: The ontology of the anatomy and development of the solitary ascidian Ciona: the swimming larva and its metamorphosis. Scientific Reports, accepted Kohji Hotta, Delphine Dauga and Lucia Manni DOI:

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