Morphogenesis defects are associated with abnormal nervous system regeneration following roboA RNAi in planarians

The process by which the proper pattern is restored to newly formed tissues during metazoan regeneration remains an open question. Here, we provide evidence that the nervous system plays a role in regulating morphogenesis during anterior regeneration in the planarian Schmidtea mediterranea. RNA interference (RNAi) knockdown of a planarian ortholog of the axon-guidance receptor roundabout (robo) leads to unexpected phenotypes during anterior regeneration, including the development of a supernumerary pharynx (the feeding organ of the animal) and the production of ectopic, dorsal outgrowths with cephalic identity. We show that Smed-roboA RNAi knockdown disrupts nervous system structure during cephalic regeneration: the newly regenerated brain and ventral nerve cords do not re-establish proper connections. These neural defects precede, and are correlated with, the development of ectopic structures. We propose that, in the absence of proper connectivity between the cephalic ganglia and the ventral nerve cords, neurally derived signals promote the differentiation of pharyngeal and cephalic structures. Together with previous studies on regeneration in annelids and amphibians, these results suggest a conserved role of the nervous system in pattern formation during blastema-based regeneration.

[1]  J. Baguñá,et al.  Proximal and distal transformation during intercalary regeneration in the planarianDugesia(S)mediterranea , 1985, Wilhelm Roux's archives of developmental biology.

[2]  R. Chandebois.  THE DYNAMICS OF WOUND CLOSURE AND ITS ROLE IN THE PROGRAMMING OF PLANARIAN REGENERATION. II — DISTALIZATION , 1980, Development, growth & differentiation.

[3]  Michael Levin,et al.  Characterization of innexin gene expression and functional roles of gap-junctional communication in planarian regeneration. , 2005, Developmental biology.

[4]  P. Reddien,et al.  Fundamentals of planarian regeneration. , 2004, Annual review of cell and developmental biology.

[5]  K. Watanabe,et al.  The role of dorsoventral interaction in the onset of planarian regeneration. , 1999, Development.

[6]  M. Singer,et al.  The Influence of the Nerve in Regeneration of the Amphibian Extremity , 1952, The Quarterly Review of Biology.

[7]  A. Droin,et al.  La Régénération caudale des Urodèles (Induction et réactivité du territoire) , 1961 .

[8]  F. Cebrià,et al.  Planarian homologs of netrin and netrin receptor are required for proper regeneration of the central nervous system and the maintenance of nervous system architecture , 2005, Development.

[9]  K. Agata,et al.  Distinct structural domains in the planarian brain defined by the expression of evolutionarily conserved homeobox genes , 1999, Development Genes and Evolution.

[10]  T. Gojobori,et al.  Dissecting planarian central nervous system regeneration by the expression of neural‐specific genes , 2002, Development, growth & differentiation.

[11]  T. Starzl,et al.  Studies on Transplantation , 1967 .

[12]  E. Maestrini,et al.  A gene deleted in Kallmann's syndrome shares homology with neural cell adhesion and axonal path-finding molecules , 1991, Nature.

[13]  R. Chandebois.  THE DYNAMICS OF WOUND CLOSURE AND ITS ROLE IN THE PROGRAMMING OF PLANARIAN REGENERATION I—BLASTEMA EMERGENCE , 1979 .

[14]  Kiyokazu Agata,et al.  Ectopic pharynxes arise by regional reorganization after anterior/posterior chimera in planarians , 1999, Mechanisms of Development.

[15]  J. Weissenbach,et al.  The candidate gene for the X-linked Kallmann syndrome encodes a protein related to adhesion molecules , 1991, Cell.

[16]  K. Agata.  Regeneration and gene regulation in planarians. , 2003, Current opinion in genetics & development.

[17]  B. Habermann,et al.  The planarian Schmidtea mediterranea as a model for epigenetic germ cell specification: analysis of ESTs from the hermaphroditic strain. , 2005, Proceedings of the National Academy of Sciences of the United States of America.

[18]  C. Goodman,et al.  Slit Is the Midline Repellent for the Robo Receptor in Drosophila , 1999, Cell.

[19]  Phillip A. Newmark,et al.  The Schmidtea mediterranea database as a molecular resource for studying platyhelminthes, stem cells and regeneration , 2002, Development.

[20]  L. Craven,et al.  The growth and morphogenesis of the regenerating forelimb of adult Triturus following denervation at various stages of development. , 1948, The Journal of experimental zoology.

[21]  V. Kiortsis,et al.  Factors of regeneration in Spirographis spallanzanii , 1965 .

[22]  C. Goodman,et al.  Slit Proteins Bind Robo Receptors and Have an Evolutionarily Conserved Role in Repulsive Axon Guidance , 1999, Cell.

[23]  S. Bryant,et al.  A stepwise model system for limb regeneration. , 2004, Developmental biology.

[24]  Phillip A. Newmark,et al.  Not your father's planarian: a classic model enters the era of functional genomics , 2002, Nature Reviews Genetics.

[25]  M. Egar.  Accessory limb production by nerve‐induced cell proliferation , 1988, The Anatomical record.

[26]  Adam L. Bermange,et al.  Identification of genes needed for regeneration, stem cell function, and tissue homeostasis by systematic gene perturbation in planaria. , 2005, Developmental cell.

[27]  M. Inatani.  Molecular mechanisms of optic axon guidance , 2005, Naturwissenschaften.

[28]  Felix V. Santos,et al.  Studies on Transplantation in Planaria , 1931, Physiological Zoology.

[29]  G. Tear,et al.  Axon guidance mechanisms and molecules: lessons from invertebrates , 2003, Nature Reviews Neuroscience.

[30]  K. Agata,et al.  Neural Projections in Planarian Brain Revealed by Fluorescent Dye Tracing , 2005, Zoological science.

[31]  Alejandro Sánchez Alvarado,et al.  Allometric scaling and proportion regulation in the freshwater planarian Schmidtea mediterranea , 2003, Developmental dynamics : an official publication of the American Association of Anatomists.

[32]  A. Sánchez Alvarado,et al.  Double-stranded RNA specifically disrupts gene expression during planarian regeneration. , 1999, Proceedings of the National Academy of Sciences of the United States of America.

[33]  K. Watanabe,et al.  Dorsal and ventral positional cues required for the onset of planarian regeneration may reside in differentiated cells. , 2001, Developmental biology.