Organization of some repetitive DNAs and B chromosomes in the grasshopper Eumastusia koebelei koebelei (Rehn, 1909) (Orthoptera, Acrididae, Leptysminae)

Abstract

B chromosomes occur in approximately 15% of eukaryotes and are usually heterochromatic and rich in repetitive DNAs. Here we describe characteristics of a B chromosome in the grasshopper Eumastusia koebelei koebelei (Rehn, 1909) through classical cytogenetic methods and mapping of some repetitive DNAs, including multigene families, telomeric repeats and a DNA fraction enriched with repetitive DNAs obtained from DOP-PCR. Eumastusia koebelei koebelei presented 2n=23, X0 and, in one individual, two copies of the same variant of a B chromosome were noticed, which are associated during meiosis. The C-positive blocks were located in the pericentromeric regions of the standard complement and along the entire length of the B chromosomes. Some G+C-rich heterochromatic blocks were noticed, including conspicuous blocks in the B chromosomes. The mapping of 18S rDNA and U2 snDNA revealed only autosomal clusters, and the telomeric probe hybridized in terminal regions. Finally, the DOP-PCR probe obtained from an individual without a B chromosome revealed signals in the heterochromatic regions, including the entire length of the B chromosome. The possible intraspecific origin of the B chromosomes, due to the shared pool of repetitive DNAs between the A and B chromosomes and the possible consequences of their association are discussed.

Keywords: Cytogenetics; DOP-PCR; FISH; Orthoptera; multigene family.

Figure 1.

Conventional staining with Giemsa in meiotic cells of Eumastusia koebelei koebelei harboring B chromosomes. a zygotene b early pachytene c metaphase I d anaphase I e metaphase II. B chromosomes are associated side by side in initial meiosis (a, b) and by centromere in other cells (c–e). These chromosomes are also segregated to the same pole in d and maintained together in metaphase II (e). X and B chromosomes are indicated. Bar: 5 µm.

Figure 2.

C-banding (a, d), CMA₃ staining (b, e, f) and FISH using as probes DOP-PCR (c, g), 18S rDNA-green and TTAGG-red (h) and U2 snDNA (i) in meiotic cells of Eumastusia koebelei koebelei with B chromosomes (d–i) and without them (a–c). a, h late pachytene b early diakinesis c, d, g diplotene e, i metaphase I f zygotene. Images d–g partially highlight B chromosomes. X, B and other chromosomes harboring specific signals are indicated; arrowheads point to the centromeres of B chromosomes. Inserts in g, h highlight B chromosomes. Bar: 5 µm.