Worm Breeder's Gazette 3(1): 25
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
As we have previously reported for light microscope studies, embryogenesis of the free-living soil nematode Caenorhabditis a strictly determinate cleavage pattern producing a newly hatched juvenile with about 550 cells quite predictably arranged. Here we present results on the electronmicroscopy of C. elegans embryos. We introduce methods for fixing, embedding and serial sectioning embryos encased in the egg shell. Fixation with either osmium tetroxide alone or with glutaraldehyde followed by osmium tetroxide at elevated temperature gives satisfactory, reproducible results with embryos in all developmental stages from the fertilized egg to hatching. With our procedures for analyzing the electronmicrographs we are able to make detailed reconstructions from serial sections of embryos of a metazoan organism. Eighteen wild type eggs at various stages have been sectioned to date. Utilizing our methods we have characterized and mapped the 24 cells of an early stage embryo. Specifically, we determined the lineage history of all cells of this embryo by matching the reconstructed 3-dimensional arrangement of this series to a living embryo at this stage, observed with Nomarski optics on video tape ( Deppe et al. 1977). In addition, cytoplasmic and nuclear morphological features, such as incomplete membranes between sister cells, rounding-off of the cytoplasm and chromatin condensation patterns, have been correlated to cell division. By mapping cells with such structures, supplementary lineage information can be obtained from electronmicrographic series. This paper is the second of a series on the electronmicroscopy of wild type embryos of the free-living soil nematode Caenorhabditis first paper on methodology we described the cellular anatomy of an early stage embryo with 24 cells as determined by reconstructions from serial section electronmicrographs (Krieg et al. 1977). Here we continue our description of the embryogenesis. We have characterized and mapped each of the 294 cells in an electronmicrographic series of a middle stage egg and thus present a complete description of a developing embryo at the cellular level . Data from this embryo are consistent with the results obtained on living eggs with the light microscope, but more detailed. Specifically we see arrangement of cells into tissues already at this stage. We also obtained supplementary lineage information for about 60 ectoderm- and mesoderm-cells of this embryo by mapping incomplete cell divisions and special chromatin condensation.