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Lecture 6

October 22 - Lecture 6 Notes - LIFESCI 2A03

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Life Sciences
Joe Kim

LECTURE 6 LIFESCI 2A03 Molecular Basis of Regeneration: Planarians as a Model System October 22, 2013 Introduction: Planaria Regeneration and Stem Cells The Problem of Regeneration – Alejandra Sanchez Alvarado, Jan 2007  Planaria – free living flat worms; related to parasitic flat worms (eg/ tape worm); live in wet environments; 3-12 mm; scavengers (Eat remains of other animals) o Centralized nervous system o Two lobes (horseshoe shape) connected to ventral cords sending projections to tip of organism; brain controls motion and musculature of organism o Muscular pharynx – from ventral surface; ingest and excrete food from same opening o Eye spots – detect light, contain pigment cup; organism avoids light o Most cells act as stem cells; can cut length wise or width wise and will regenerate entire body o Regeneration is fast and robust; decapitate animal, can regenerate in 7 days to fully functioning organism  Day 1 – wound healing  Day 2 – unpigmented area; forming epithelium  Day 3 – regeneration blastema; white pigmented tissue  Day 4 – beginning of photoreceptors (notice anlage); neurons form, pigment cups form, photoreceptors emerge  Day 5 – complete differentiation of missing structures  Day 7 – planaria completely competent to respond to light, food, touch o Schmidtea mediterranea – bilaterally symmetric; derivatives of all 3 germ layers form  Complex organ system that sit on top of each other (layers)  Gastrovascular system – food processing to serve as a source of carbon; enters through single opening (part of pharynx) to gut, then dispersed to body; food not digested is excreted from same pharyngeal opening  Excretory system – protophrania; dorsal surface, equivalent to kidneys, two cephalic ganglia sitting on top of 2 ventral cords that traverse to top of animal; neuronal contact between two ventral cords that traverse to anterior-posterior axis  Sexual and Asexual Biotypes  Sexual o Hermaphrodites (testes and ovaries) yet cannot self fertilize  Asexual o Arose as a result of a chromosomal translocation (from chromosome 1  3); cannot sexually reproduce  Pinches off at waist to produce two segments that each regenerate to form a full clone o Focus most on asexual biotypes for studies o Small genome, 700 Mb (nucleotides) o Locomote by cilia that beat in one direction; musculature lifts head and turns body o Regenerative capacity and plasticity root in neoblasts (undifferentiated cells) that populate the majority of the body  Modern research with planaria o Simple organism can allow us to extrapolate findings to humans o Found 240 genes involved in regeneration o Smed-wi in planaria – maintenance of stem cells and regulating function of daughter cells (daughter cells cannot regenerate  Analogous to piwi in drosophila  Distinguishing stem cells from other cells in the planaria o Morphology – large nucleus, little cytoplasm o Cell-surface or intracellular protein markers – different expression in stem cells and other cells (eg/ in niche) o Cell proliferation – mitotic divisions in stem cells  Techniques 1. Labeling dividing cells a. BrdU Labeling b. H3P
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