Reddien and Alvarado, 2004

Reddien and Alvarado, 2004 - Annu. Rev. Cell Dev. Biol....

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Unformatted text preview: Annu. Rev. Cell Dev. Biol. 2004. 20:72557 doi: 10.1146/annurev.cellbio.20.010403.095114 Copyright c 2004 by Annual Reviews. All rights reserved First published online as a Review in Advance on July 2, 2004 F UNDAMENTALS OF P LANARIAN R EGENERATION Peter W. Reddien and Alejandro Sanchez Alvarado University of Utah School of Medicine, Department of Neurobiology and Anatomy, Salt Lake City, Utah 84132-3401; email: sanchez@neuro.utah.edu, reddien@neuro.utah.edu Key Words stem cells, blastema, epimorphosis, morphallaxis, flatworm Abstract The principles underlying regeneration in planarians have been ex- plored for over 100 years through surgical manipulations and cellular observations. Planarian regeneration involves the generation of new tissue at the wound site via cell proliferation (blastema formation), and the remodeling of pre-existing tissues to re- store symmetry and proportion (morphallaxis). Because blastemas do not replace all tissues following most types of injuries, both blastema formation and morphallaxis are needed for complete regeneration. Here we discuss a proliferative cell population, the neoblasts, that is central to the regenerative capacities of planarians. Neoblasts may be a totipotent stem-cell population capable of generating essentially every cell type in the adult animal, including themselves. The population properties of the neoblasts and their descendants still await careful elucidation. We identify the types of structures produced by blastemas on a variety of wound surfaces, the principles guiding the re- organization of pre-existing tissues, and the manner in which scale and cell number proportions between body regions are restored during regeneration. CONTENTS INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 726 Anatomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 726 Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 728 THE PLANARIAN BLASTEMA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 729 Responses to Wounding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 729 Possible Cues for the Initiation of Regeneration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 729 Cell Proliferation, Cell Migration, and the Regeneration Blastema . . . . . . . . . . . . . 730 THE CELL BIOLOGY OF PLANARIAN REGENERATION . . . . . . . . . . . . . . . . . . 731 What Are Neoblasts? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 731 What Is the Source of Neoblasts? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 733 Neoblast Migration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 735 PROPERTIES OF BLASTEMA FORMATION...
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Reddien and Alvarado, 2004 - Annu. Rev. Cell Dev. Biol....

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