1. Multicellularity Colonies: cyanobacteria and choanoflagellates
Sponges as organisms
Picture is of an integrin-linked ILK(integrin-linked kinas) antibody.
Picture source:
Adv Immunol. 1999;72: Links
Integrins in the immune system.
Shimizu Y, Rose DM, Ginsberg MH.

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

3. Figure 26.3x2 Filamentous cyanobacteria from the Bitter Springs Chert
Frank et al. 2003: cyanobacteria specialize to protect nitrogenases as oxygen rises in atmosphere.
Origin of life is covered on pp of chapter 26, Tree of Life

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
There are three kinds of cells here, each with a different function:
vegetative cells – photosynthesis
heterocysts – nitrogen fixation
Oxygen began building up in the atmosphere (after precipitating a LOT of iron) about 2 biliion years ago.
akinetes – resistant cells forming spores under bad conditions

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. Figure 32.8 Animal phylogeny based on sequencing of SSU-rRNA
colonial choanoflagellate
See Maldonaldo This paper questions the choanoflagellate as metazoan-sister argument in doubt, while addressing a number of themes relevant to multicellularity and sponge evolution.
See Roy 2005 for problems with arthropod sister group analysis.
Nicole King, Christopher T. Hittinger, Sean B. Carroll* 2003 Evolution of Key Cell Signaling and Adhesion Protein Families Predates Animal Origins. Science 301: 361 – 363
The evolution of animals from a unicellular ancestor involved many innovations. Choanoflagellates, unicellular and colonial protozoa closely related to Metazoa, provide a potential window into early animal evolution. We have found that choanoflagellates express representatives of a surprising number of cell signaling and adhesion protein families that have not previously been isolated from nonmetazoans, including cadherins, C-type lectins, several tyrosine kinases, and tyrosine kinase signaling pathway components. Choanoflagellates have a complex and dynamic tyrosine phosphoprotein profile, and cell proliferation is selectively affected by tyrosine kinase inhibitors. The expression in choanoflagellates of proteins involved in cell interactions in Metazoa demonstrates that these proteins evolved before the origin of animals and were later co-opted for development.

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

10. Multicellularity Colonies: cyanobacteria and choanoflagellates
Sponges as organisms

11. Figure Sponges

12. Figure 33.3 Anatomy of a sponge
individuation (i,e, origin of an immune system) is essential to being a metazoan --- develop this concept using mueller 2003.
The aggregation of cells into groups is also key. The key molecules here are integrins. For sponges, the key reference is Pancer 1997.
In this paper they report integrins plus signaling proteins with high homology to higher metazoans and argue for metazoan status for the sponges.
The whole significance of the integrins is that they are involved BOTH in aggregation of cells and transduction of signals, and they are unusual in sending signals both ways across the cell membrane.

13. It’s what’s between cells that defines multicellularity in animals.
-The extracellular matrix is important here --- see which reveals that animals have a cell-wall equivalent, it’s just more elastic.
The ECM is perhaps key to defining organism – components include the glycoproteins collagen, fibronectin, and proteoglycans.
See Campbell Ch 6 (cell biology) p (cells wasll here too)

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.
Interactions between cells and their extracellular environment play an essential role in controlling tissue architecture, cell survival, and cell migration. These processes are important for normal animal development and are disrupted during cancer progression.
Integrins are cell surface proteins that sense the extra cellular protein (matrix) environment and signal to the cell to control differentiation, survival and migration of cells. In animals there are multiple integrins with specialized and overlapping roles in various cell types. From Cram lab text – berkeley
images:

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

16. Multicellularity Colonies: cyanobacteria and choanoflagellates
Sponges as organisms