Endomitosis in grasshoppers. I. Nuclear morphology and synthesis of DNA and RNA in the endopolyploid cells of the inner parietal layer of the testicular follicle.

Changes in chromosome number (n-16n) due to somatic polyploidization were observed in the inner parietal layer cells (IPLCs) of the testicular follicle in 30 grasshopper species. A distribution into a geometrical series originating from the diploid value was established for the chromosome number of most of the nuclei of the IPLCs. However, nuclei with chromosome numbers of n, 3n, 5n, 7n were also found. POLYPLOId cells showed morphological patterns indicative of classical endomitosis. Endometaphase was most frequently encountered in the IPLCs. At this stage, the chromosomes were sufficiently condensed so that they were individually identifiable and their numbers could be counted. A Feulgen stain-positive fibrillar halo around the central part of chromosomes produced a lampbrush-like appearance. It was shown that the presence of many endometaphases in the IPLCs was not correlated with intense chromosome replication. 3H-thymidine incorporation data as well as cytophotometric DNA measurements did not demonstrate any appreciable DNA synthesis in the IPLCs. However, these cells were found to incorporate intensely 3H-uridine, especially in the endometaphase stage. Based on these data a reconsideration of the morphological patterns of endomitosis is suggested. The chromosomes of endopolyploid cells are considered as suitable models for studies of the functional organization of actively transcribed, individually visible chromosomes.