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Choanoflagellate morphogenesis, interspecies signaling and the origin of animal multicellularity

Choanoflagellate morphogenesis, interspecies signaling and the origin of animal multicellularity. Nicole King Molecular and Cell Biology - UC Berkeley Clark Ctr. Auditorium, 3 :15pm , Thursday (10/29) Tristan Ursell Huang Group. The Questions.

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Choanoflagellate morphogenesis, interspecies signaling and the origin of animal multicellularity

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  1. Choanoflagellate morphogenesis, interspecies signaling and the origin of animal multicellularity Nicole King Molecular and Cell Biology - UC Berkeley Clark Ctr. Auditorium, 3:15pm, Thursday (10/29) Tristan Ursell Huang Group

  2. The Questions 1) When and under what conditions did the first multi-cellular metazoans evolve? 2) What genetic and molecular adaptations led to the rise of multi-cellularity? 3) Are there living relatives of the first organism(s) to make this evolutionary jump?

  3. The Background The fossil record: Prokaryotes: 3200 mya Eukaryotes: 2100 mya First metazoans: 600 mya Humanoids: 2 mya Simplest living metazoan: Porifera (sponges)

  4. What are we looking for? … in a model organism: - unicellular or colonial, living eukaryote - high genetic similarity in specific genes to simplest living metazoan - high morphological similarity to simplest living metazoan - there may (are) only be limited species to choose from.

  5. Evolutionary Advantages What selective advantage does MC impart? predation avoidance model predator-prey systems show heritable selection for multi-cellularity in prey Cellular multi-tasking and specialization temporal competition for the same cellular machinery in motility (basal body) and mitosis (mitotic spindle)

  6. Evolutionary Requirements What problems need to be solved? - Cell-cell adhesion - collagen, integrins - Cell-cell signaling - receptor tyrosine kinases - Spatial differentiation - more complex regulation through transcription and RNAs

  7. Evolutionary Requirements Have they been examined by unicellular life? - Cell-cell adhesion - heterotrophic protozoa –> specific binding of predator and prey - Cell-cell signaling - quorum sensing, friend / foe recognition - Temporal differentiation - sporulation, dormancy, foraging

  8. Identifying Candidates How do we identify a candidate last unicellular metazoan ancestor? - Phylogenetics as generated from mitochondrial and genomic DNA sequencing - Morphological (and in some sense phenotypic) comparison.

  9. Multiple Lineages Phylogenetic analysis suggests: Multiple transitions across all life Probably a single transition for metazoans - ribosomal RNA and low copy nuclear genes

  10. Multiple Lineages Phylogenetic analysis suggests: 3) Clustering indicates a genetic predisposition for MC in certain lineages

  11. Multiple Lineages Phylogenetic and morphological analyses suggest: Metazoans might have multiple distinct origins. - What would metazoan polyphyly imply?

  12. Identifying Candidates Choanoflagellates - unicellular, aquatic eukaryotes - heterotrophic (i.e. non-photosynthetic) - bare close morphological homology with Poriferanchoanocytes (foraging cells of sponges) - this morphology / cell-type unique to choanoflagellates and metazoans - protein sequencing places them with metazoans and distances them from fungi - rRNA studies put other amorphological species at the metazoan – fungi internode

  13. Identifying Candidates Striking resemblance observed as far back as 1868.

  14. Identifying Candidates All that said: - it is difficult to assess whether CFs are a ancestral or degenerate taxon. - as of 2005, protein sequencing of multiple CFs and sponges failed to make this distinction. - however, mtDNA sequencing suggests CFs are a genuine ancestor - metazoan mtDNA has fewer genes and lacks intergenic regions found in CFs

  15. Minimal Ancestral Genome What requirements determine the minimal ancestral genome of metazoans that pre-adapts for MC? - determine the unique set of genes shared by CFs and metazoans that do not have homologs in other phyla (CFs express many ‘animal-only’ genes) - over 800 protein domains are found only in metazoa (e.g. integrins, tyrosine kinases) - some domains used in metazoa cellular interactions are found in unicellular eukaryotes, suggesting pre-adapted use

  16. Mechanisms of Evolution What evolutionary changes were needed for MC to arise? 1) protein evolution –> new functions 2) regulatory evolution –> differentiation On a molecular level, how might these be achieved? 1) gene duplication and divergence 2) domain shuffling 3) multiple inputs, modular regulatory region design, relaxed spatial constraints

  17. Choanoflagellate morphogenesis, interspecies signaling and the origin of animal multicellularity Nicole King Molecular and Cell Biology - UC Berkeley Clark Ctr. Auditorium, 3:15pm, Thursday (10/29) Tristan Ursell Huang Group

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