Worm Breeder's Gazette 8(1): 32
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.
DNA replication is normally a prelude to cell division but, in certain tissues, DNA synthesis occurs without mitosis or cytokinesis, producing cells with polyploid nuclei. We have been examining the timing and extent of such endoreduplication using Hoescht 33258 to stain DNA (Albertson et al., 1978). Video pictures of florescent nuclei were digitized using an Intellect 100 image processor and the florescence intensity of each nucleus was calculated. Tentative conclusions for the intestine and lateral hypodermis are illustrated by the figure below. The approximate times of DNA synthesis are indicated by an S. DNA contents are given as multiples of the haploid content C. Neurons and body muscles are diploid (2C) throughout larval development. The twenty intestinal cells are diploid at hatching. The posterior 14 cells usually undergo a round of DNA synthesis and a nuclear division near the beginning of the L1 lethargus (Sulston and Horvitz, 1977) and become binucleate cells with two diploid nuclei. The anterior 6 nuclei do not normally divide. The DNA contents of all of the intestinal nuclei increase during subsequent larval growth, doubling once each intermoult. The times of the doublings are not known, except for the L1 stage where doubling appears to occur in the lethargus soon after the nuclear divisions. Some of the syncytial nuclei of the lateral hypodermis are tetraploid. These nuclei, generated by the seam cells during larval growth, undergo a round of DNA synthesis just prior to cell fusion with the syncytium. Interestingly, the embryonic hypodermal nuclei remain diploid and postembryonic nuclei derived from the ventral hypodermal precursors (Pn) are also probably diploid. Thus, nuclei of different DNA contents exist within the same syncytial cell. [See Figure 1]