Sponges display a remarkable degree of morphological plasticity and regenerative capacity. They can be dissociated into individual cells, which can then re-aggregate and fully regenerate to a juvenile stage animal. But to what extent does this regenerative process mimic normal development? Vengamanaidu Modepalli and colleagues set out to address this question at both a morphological and transcriptomic level in the sponge Sycon ciliatum. First, they develop a robust protocol to analyse regeneration in a semi-synchronous manner across multiple aggregates, and then characterise in detail the dynamic changes in cell-type composition and morphology that occur over the course of regeneration. They show that, while early stages bear little resemblance to developmental stages, subsequent phases show striking similarities to post-larval development. This morphological similarity between later stages of development and regeneration is also reflected in the transcriptome profiles; many key developmental signalling pathways and regulators of, for example, cell adhesion and migration are also upregulated during regeneration, and may be playing similar roles at equivalent stages. These datasets set the stage for further in-depth analysis of sponge regeneration, and – given the similarity between sponge collar cells and choanoflagellates (the sister group to metazoans) – may help inform our understanding of the origins of multicellularity.
