In the present study we examined the pattern of cell survival versusdeath of the MP3 progeny in 472 embryos from four different species, from the genetically ...
J. Embryol. exp. Morph. 78, 169-182 (1983) Printed in Great Britain © The Company of Biologists Limited 1983
Neuronal cell death in grasshopper embryos: variable patterns in different species, clutches, and clones By CURTIS M. LOER 1 - 3 , JOHN D. STEEVES 2 AND COREY S. GOODMAN 1 From the Department of Biological Sciences, Stanford University
SUMMARY Previous studies showed that cell death plays an important role in adjusting the segmentspecific number of ganglionic neurones during grasshopper embryogenesis (Bate, Goodman & Spitzer, 1979; Goodman & Bate, 1981). In every segment, the single midline precursor 3 (MP3) divides once to produce two progeny. In some segments, one or both of these two progeny die; there is a general pattern of cell death of the MP3 progeny across the thoracic and abdominal segments. In the present study we examined the pattern of cell survival versus death of the MP3 progeny in 472 embryos from four different species, from the genetically related offspring within different clutches of the same species and from the genetically identical offspring within isogenic clones of the same species. We find variability in the pattern of cell survival versus death amongst embryos of the same species, clutch and clone, suggesting a significant epigenetic influence on this pattern. However, our results also show significant differences in the pattern of cell death between different genera and species, and between different clones and clutches within a single species, suggesting a genetic influence on this pattern as well.
INTRODUCTION
Each segmental ganglion in a grasshopper's metameric nervous system contains a highly specific pattern of neurones. From segment to segment, this pattern varies; each segment's complement of neurones is tailored to that segment's particular needs. One of the most striking differences between segments is the number of neurones; thoracic ganglia contain about 2000 neurones whereas abdominal ganglia contain about 500 neurones. Each different segmental pattern is produced, however, from a common segmentally repeated set of precursor cells (Bate, 1976; Bate & Grunewald, 1981; Goodman, Bate & Spitzer, 1981; Goodman & Bate, 1981). The differences in cell number arise in two ways: 1
Authors' address: Department of Biological Sciences, Stanford University, Stanford, CA 94305, U.S.A. 2 Author's address: Department of Zoology, University of British Columbia, Vancouver, BC3 V6T 2A9, Canada. Author's present address: Biology Department B-022, University of California, San Diego, La Jolla, CA 92093, U.S.A.
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differential production of cells by the neuronal precursors and differential death of the cells produced. Cell death appears to play the more important role in adjusting cell number; segmental differences are sculpted from a common block rather than constructed differently from the outset (Bate, Goodman & Spitzer, 1981; Goodman & Bate, 1981; Bate & Goodman, in preparation). This is illustrated by the progeny of one of the identified neuronal precursor cells, the median neuroblast (MNB). In the metathoracic (T3) segment, the MNB produces about 100 progeny, most of which survive. In the first abdominal segment, the MNB produces about 90 progeny, only 45 of which survive; thus cell death accounts for most of the segment-specific difference in cell number from this NB (Goodman & Bate, 1981). At specific stages of embryogenesis, there is massive cell death in the abdominal segments while there is relatively little death in the thoracic segments. Interestingly, many cells destined to die begin their morphological differentiation before they die (Bate & Goodman, in preparation). Whether cells in the
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