BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Talks.cam//talks.cam.ac.uk// X-WR-CALNAME:Talks.cam BEGIN:VEVENT SUMMARY:The fossil origins of eukaryotic morphogenesis: exploring the begi nnings of complex multicellularity in the Holozoa - Paul K. Strother (Bos ton College) DTSTART:20220228T143000Z DTEND:20220228T153000Z UID:TALK168998@talks.cam.ac.uk CONTACT:Elena Scarpa DESCRIPTION:The fossil record is a (backwards) time machine that provides us with the occasional snapshot of former life on Earth. Phosphatic nodule s from the Torridonian Sequence in in the NW Scottish Highlands preserve l ake bottom sediments from 994 ± 48 Ma and some layers include 3-dimension ally preserved cells and cell clusters. The simple morphologies of unicell ular organisms throughout much of the Precambrian record have permitted th e recognition of only a handful of protist-level clades. The Torridonian\, however\, has preserved more complex morphology in the form of various ce ll clusters\, some of which contain 2 clearly distinct cell types. A proce ss of elimination\, based on cell-cell morphology led us to propose the Ic hthyosporea as the closest morphological analog to this new form\, Bicellu m Brasieri. Nick Butterfield pointed out years ago that individual Precamb rian deposits might be conducive to the preservation of life-cycle varieti es\, and\, indeed\, we found several populations of what we infer to be th e intermediate phases in the Bicellum life cycle. These include the initia tion of multicellularity through the formation of a (multinucleate) syncyt ium\, followed by cellularization into isodiametric cells forming a parenc hymatous stereoblast. Some stereoblasts preserve an admixture of a small n umber of elongate cells within the largely isodiametric cell mass. Others show a single enclosing layer of elongate cells\, that we infer to have mi grated to the periphery of the cell mass. In the inferred mature\, cyst\, form\, the elongated cells have thickened walls and they are devoid of cel l contents. \n\nEven though the dynamics of this reconstruction are specul ative\, fossil themselves do provide the basis for an independent morphoge nic model from which to explore the early evolution of morphogenesis eukar yotes. For example\, Malcolm Steinberg’s Differential Adhesion Hypothesi s (DAH) provides a possible causal mechanism for the movement of elongate cells to the cell mass periphery. Similar dynamics have been shown in both adhesion experiments with living cell masses and computer simulations. It is interesting to speculate that mechanistic aspects of development in ea rly eukaryotes may have incorporated a combination of D’Arcy Thompsonian ‘physical forces’ (or Kauffman’s ‘order for free’) in conjuncti on with the chemical environmental signalling that eventually led to genet ic control of cell development and differentiation in the evolving holozoa n lineage. The extent to which such elements will become incorporated into new models of hypothetical protistan ancestors to the Metazoa remains to be seen\, but Bicellum does demonstrate that simple cell-sorting in protis ts was taking place in lake bottoms almost a billion years ago. LOCATION:Online END:VEVENT END:VCALENDAR