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Lecture 3

Lecture 3 - September 17 - LIFESCI 2A03

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McMaster University
Life Sciences
Joe Kim

LECTURE 3 LIFE SCI 2A03 Lecture 3 - Regeneration September 17, 2013  Regeneration – the regrowth of lost or destroyed parts or organs  Plants commonly show regeneration o Plant cutting is a technique used to produce a clone of a plant (vegetative or asexual reproduction) o A whole adult plant can regrow from a piece of a plant; a piece of stem, leaf or root o Individual stem cells are losing identity as stem cells – assuming identity of root cells o A classic experiment illustrated in carrots – differentiated root cells from a carrot plant can regrow into an entire plant  Separate cells from carrot, culture cells, individual cells will then be able to generate entire new plant  Regeneration in plants illustrated o Plants – always growing o Figure: Arabidopsis Root Regeneration  Regeneration in animals o Animals stop growing – must reactivate system of growth and development o A few invertebrates with simple body plans demonstrate bi directional regeneration where both cut sides can regenerate o Process of clonal reproduction o Eg/ Animals with radial symmetry; hydras, sea stars, anemones Eg/ Planaria bidirectional regeneration  Planaria – non-parasitic flatworm that exhibits an extraordinary ability to regenerate  Bidirectional Regeneration – the ability to regenerate whole bodies from small tissue fragments o Eg/ Hydra – cut in half; two new hydra that are smaller will regenerate that can each grow to the original adult size through cell division  Figure: Cut in 3 places; all 3 pieces can regenerate to full planaria  Steps: 1. Muscular contraction to limit size of cut surface 2. Thin wound epithelium forms over surface 3. Accumulation of undifferentiated cells (neoblasts) in the blastema 4. Growth and differentiation of blastema 1 LECTURE 3 LIFE SCI 2A03  Blastema – a mass of undifferentiated cells capable of growth and regeneration into organs or body parts; found in the early stages of embryonic development and in the regeneration of tissues, organs and bone o Similar to egg fertilized by sperm in embryonic development (embryonic blastema)  Neoblasts – regenerative cells within the blastema; small undifferentiated mitotic cells that comprise about 20% of the worms body they act as stem cells for growth an regeneration o No regeneration can occur if there are no neoblasts cells (eg/ near pharynx) o Neoblasts are like embryonic stem sells – develop into all cell types  Polarity o The first decision that the blastema makes is what portion of the body to regenerate: head or tail – difference in polarity o Information is contained within amputated fragment o Mechanism for polarity is not known  Same factors used in embryogenesis are involved  Studies to try to identify the mechanism have come from:  Studying errors – small fragment capable of regeneration, but is missing directional information (results in two heads)  Experiments that examine grafts from one organism to another – graft blastema from one organism to another; remove head of original organism; observe  Neoblasts exhibit pluripotency – demonstrating the ability to become any different cell type o Pluripotent – the ability to differentiate or become any cell type in the body o Isolated single neoblasts cells and cultured them in vitro (cNeoblasts) – cells able to differentiate into neuronal, intestinal and other known adult cell types o Single transplanted cNeoblasts restored regeneration in animals unable to regenerate o Confirmation of pluripotent quality of neoblasts  Experiment – kill neoblasts cells in adult planaria to prevent ability to regenerate; add single cNeoblasts to planaria  regeneration is restored from single neoblasts; must be capable of taking on all cell types 2 LECTURE 3 LIFE SCI 2A03 Other Organisms – Salamanders  Monodirectional Regeneration – regeneration of appendages that proceeds distally from cut on site  In insets and vertebrates, regeneration can only result in the replacement of lost appendages, not whole organisms from a part o Eg/ Cockroach and Amphibian – cut off a leg; body can regrow leg; leg cannot regrow body o Most urodele amphibians (salamanders) can regenerate throughout their lives  Regeneration in Salamanders o Different stages of regeneration 1. Wound Healing 2. Dedifferentiation – cells losing identity; muscle cells no longer muscle cells; reforming shape and level of gene and protein expression; lost specific muscle fate 3. Differentiation – cells become certain type o Takes about 40 days to form new limb o Blastema – dedifferentiated cells that accumulate at the end of the stump; the group of cells that will form the new limb  Contains positional information – the regeneration blastema grows and differentiates in a proximal to distal fashion; the small limb then grows to adult size and is indistinguishable from the original  Distal = away from the body  Proximal = close to the body o Early experiments in regeneration focused upon investigations of polarity and patterning  Experiment 1 – remove “hand” on forelimb and graft stump to body, remove forelimb from body (so that “hand stump” is grafted to side”  arm grows on side where grafted and where forelimb was located before  Experiment 2 – cut forelimb and hindlimb; graft piece of forelimb stump to hindlimb stump  regenerated 3 limbs; 2 on hindlimb stump (one with forelimb info, one with hindlimb info) + 1 where forelimb was located before  Experiment 3 - o Regenerative cells in blastema act like stem cells  Undifferentiated – cells move around and leave original structure
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