The role of choanocytes in the sponge stem cell system and their suggested homology with choanoflagellates

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• Shunsuke Sogabe (University of St Andrews)
• Wednesday 31 January 2018, 13:00-14:00
• Part II Lecture Theatre, Department of Zoology.

If you have a question about this talk, please contact Martin Minarik.

Metazoan multicellularity required the evolution of cellular processes such as cell differentiation, cell-cell adhesion and communication, along with complex gene regulatory networks and the emergence of a stem cell system. Choanocytes, the collared feeding cells in sponges, have been extensively compared with choanoflagellates due to their morphological similarities and their capacity to form multicellular structures. Recent studies on the choanoflagellate Salpingoeca rosetta, revealed many genes shared with metazoans are upregulated only when the S. rosetta cells form colonies. On the other hand, choanocytes have been suggested as playing a part in the sponge stem cell system, but there has been little progress on understanding the development and general biology of sponge choanocyte chambers. Here, we have documented the formation and maintenance of choanocyte chambers in the demosponge Amphimedon queenslandica, using cell trackers and proliferation assays, showing their dynamic nature in the sponge body. Contrary to previous studies in sponges as well as choanoflagellate colonies, we found that choanocyte chamber development is not always clonal. After metamorphosis, choanocytes in these chambers are also capable of dedifferentiating into archeocytes (primary stem cells), which can subsequently differentiate into multiple cell types including new choanocytes. We propose that choanocyte chambers in A. queenslandica are playing a central role in the stem cell system, increasing and maintaining the stem cell population. We have also obtained cell-type specific transcriptomes, with a number of analyses between choanocytes and choanoflagellate datasets showing no strong evidence of a shared gene repertoire. The results from our studies suggest that the similarities between choanocytes and choanoflagellates are likely the product of convergence, and it is time we revisited their assumed homology.

This talk is part of the Evolution and Development Seminar Series series.

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