L312/Spring 2003Lecture 22Drummond April 7 For today: Start Chapter 21; tissue structure and connections today (skip plant tissues) Last time: Anaphase initiation by APC (anaphase promoting complex) : triggers inhibitor degradation active protease degrades cohesins, metaphase progresses to anaphase MAPs and catastrophins in maintaining a steady state involving microtubules failure to degrade: long strings/hair failure to stabilize: short, unconnected Critically compare features of microtubules and MAPs in mitosis XKCM-1 (catastrophin) and XMAP-215 (X = xenopus, a favored frog) Finish: Steps in anaphase: anaphase A: kinetochore microtubules shorten anaphase B: interpolar microtubles lengthen and slide; centrosomes move apart The steps in mammalian cytokinesis The role of actin and myosin This time: Tissues (connective, epithelial, etc.) and the extracellular matrix What holds cells together? What gives tissues strength?

MAPs bind microtubules and modulate stability and function XMAP215 XKCM1 Antibody depleted Antibody depleted Antibody depleted Implications: [MT]? [GTP]?

Actin and myosin are central to cell resolution into two cells What are possible roles for the interpolar microtubules at this late stage? Initiated in anaphase

What happens to the integrins during cytokinesis? what is the key molecular event That mediates integrin release?

Stepping back: cells in the context of structure What and where is the extracellular matrix? Who makes it? What role does each cell type serve? Where do you think tumors arise? Tendons Bone Cartilage Eye matrix

What is the primary protein structure that provides ECM strength? Compare to cell Dimensions! 1/4th of your protein Collagen A ~1000 aa long (+elastin, keratin, And others) What distinguishes these from IFs? What are the dots? Tendons Bone Cartilage Eye matrix Secretion and assembly? Fibroblasts?

How are collagen Fibers crosslinked?

Vitamin C is essential for crosslinking collagen (deficiencies result in weakened skin, teeth, bones) * *

James Morris couldn’t cross-link his collagen

Packing of collagen fibers leads to a banding pattern

Stripped ECM reveals collagen and fibroblasts

Perpendicular layering of collagen fibrils in skin (and elsewhere) How do you make Collagen fibers into A strong skin Network?

Bone cells (osteoblasts)/osteoclasts in a connective matrix Where is the bone? Where is the collagen?

Integrins mediate transmembrane interactions What else? The shallow lake analogy

Glycosaminoglycans (GAGs) are long, negatively charged polymers What role do these ECM components play? Why are they sulfated? (polymer = hyaluronan)

Proteoglycan structure in the ECM