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Evolution of Multicellularity: Cyanobacteria, Choanoflagellates & Sponges

Explore the ancient origins of multicellularity through colonies of cyanobacteria, choanoflagellates, and sponges. Discover key evolutionary events and cellular differentiation processes. Uncover the role of integrins and enzymes in animal evolution.

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Evolution of Multicellularity: Cyanobacteria, Choanoflagellates & Sponges

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  1. Colonies: cyanobacteria and choanoflagellates • Sponges as organisms Multicellularity

  2. Cyanobacteria - among the oldest fossils Stromatolite section Stromatolites: colonies of cyanobacteria

  3. Figure 26.3x2 Filamentous cyanobacteria from the Bitter Springs Chert

  4. Figure 26.2 Clock analogy for some key events in evolutionary history

  5. Figure 27.11 The cyanobacterium Anabaena and its nitrogen-fixing heterocysts

  6. Development and communication in Anabaena Crucial components need to be identified to understand the process of heterocyst cellular differentiation. What is the switch that commits a cell to differentiate? How is transcription controlled at different stages of development? Is there a single master transcriptional regulatory control or do several regulators work in parallel? What mechanisms are involved in expression of the nitrogen-fixation genes?

  7. Figure 26.1 Some major episodes in the history of life

  8. colonial choanoflagellate Figure 32.8 Animal phylogeny based on sequencing of SSU-rRNA

  9. Enzymes typical of true animals (metazoans) are found in their colonial protist anscestors, e.g. tyrosine kinase is found in choanoflagellates. tyrosine

  10. Colonies: cyanobacteria and choanoflagellates • Sponges as organisms Multicellularity

  11. Figure 33.2 Sponges

  12. Figure 33.3 Anatomy of a sponge

  13. It’s what’s between cells that defines multicellularity in animals.

  14. Integrins are cell-surface proteins that sense the extracellular protein (matrix) environment and signal to the cell to control differentiation, survival and migration of cells.

  15. Figure 26.2 Clock analogy for some key events in evolutionary history

  16. Colonies: cyanobacteria and choanoflagellates • Sponges as organisms Multicellularity

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