Dictyostelium discoideum Slime Molds: The Social Amoebae 10 um 2 mm 10 5 cells.

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Presentation transcript:

Dictyostelium discoideum Slime Molds: The Social Amoebae 10 um 2 mm 10 5 cells

Life Cycle Diploid amoebas Haploid amoebas FusionMeiosis starvation Dispersal

The Dictyostelium Genome 6 chromosomes 33.6 Mb of DNA (77%[A+T]) 12,500 ORFs

Heterotrophic Feeding by Phagocytosis Movie

Actin Microfilament-Based Motility Drives Cell Movements Myosin II::GFP Actin::GFP Movie

The Microtubule Cytoskeleton Is Not Involved in Motility Tubulin::GFP Bacteria in phagosomes Movie

Mitosis and Cytokinesis Tubulin and Actin Myosin I and Myosin II Actin and Myosin II

Chemotaxis to cAMP Movie

Chemotaxis Triggers a Signal Transduction Cascade + cAMP cAR Heterotrimeric G-protein PLC  GTP IP 3 Actin Assembly Ca++ ER High Ca ++ Low Ca ++

Starving Cells Coordinate with cAMP Pacemaker Centers Trigger Spiral Waves of Cellular Movements

Responding to the Call... Phosphodiesterase outside cAMP outside cAR Receptor cAMP inside AdenylateHeterotrimeric CyclaseG-protein Movie Pacemaker center Movie

Differentiation is also Controlled by cAMP

Differential Gene Expression Prestalk cells (cAMP lower) Prespore cells (cAMP higher) Spore differentiation factor Light + Chlorinated hexanone DIF SDF-2

Slug Formation Prestalk cells Prespore cells (tagB::GFP) (cotB::GFP) leaders followers Video: 1.25 hr total time Chlorinated hexanone

Cells Assume Different Fates Depending on Their Location in The Slug Fluorescent reporters driven by differentiation- specific promoters PrestalkA::GFP and PrestalkO::RFP (i.e. subpopulations of stalk cells)

Culminant Structure

Morphogenesis!

The Morphogenetic Progression (24hr)

A Few Questions for Thought Describe, in your own words, the Dictyostelium life cycle. Review your notes from the first semester on microfilament (actin)/myosin-based cell motilities and integrate that with the Dictyostelium model. Review your notes from previous quarters on cell signaling - the roles of cAMP, G-proteins, phosphoinositides (IP 3 ), Calcium ions and kinases in how cells transduce, amplify and respond to changing environmental conditions. Describe the cooperative nature of culminant formation, considering how and why certain cells contribute to the structure by forming a stalk or spores. Consider how “cheaters” emerge in this process and how that might bring an immediate reward but ultimately prove a poor strategy for life (a very Haverfordian lesson).