Disproportionate numbers of rDNA loci in diploid and polyploid testis nuclei of gerris najas detected by fluorescence in situ hybridization

Abstract

The replication state of rDNA in testes nuclei undergoing polyploidization by classical‐type endomitosis was investigated in Gerris najas (Heteroptera) by means of fluorescence in situ hybridization. The number of just one rDNA locus per haploid genome was determined by in situ hybridization on meiotic nuclei. Additionally, DNA measurements of spermatids and testes nuclei were performed. Although regular duplication levels of nuclear DNA were found within the limits of the accuracy of the method, these did evidently not apply to the ribosomal genes. The comparison of the number of rDNA signals with the DNA content of 106 testis nuclei revealed drastic variations of the number of rDNA loci between individual nuclei with similar DNA content. Polyploid nuclei of the testis epithelium showed too low numbers of rDNA loci in relation to those expected from the levels of ploidy, while cyst cell nuclei displayed increased numbers of rDNA loci. The results indicate that the ribosomal genes are either underreplicated, or in part eliminated, during the endomitotic cycles of epithelium cell nuclei, but amplified in the cyst cell nuclei, probably already at their diploid stage.

DNA content, interphase AgNOR-area, number of3HrDNA hybridization signals and the methylation level in coding rDNA sequence in different organs ofLupinus luteus L.

“…The number of fluorescence signals after in situ rDNA/DNA hybridization is lower in the testis epithelium than expected from the DNA content, therefore, rDNA is underreplicated during successive endomitotic cycles. On the other hand, in cyst cell nuclei, genes coding for rRNA seem to be overreplicated (Becker & Nagl, 1994). Therefore, one can assume that in the upper part of the root in Lupinus luteus rDNA underreplication occurs, similarly to Zea mays (Olszewska et al, 1981).…”