Characterization of the heterochromatin of the darkling beetle Misolampus goudoti: cloning of two satellite DNA families and digestion of chromosomes with restriction enzymes.

Abstract

The darkling beetle Misolampus goudoti Er. has 58% of C-banded chromosome material. In this paper we deal with the study of the heterochromatin of this insect both by molecular and cytogenetical methods. Two different satellite DNA families have been characterized in Misolampus goudoti by agarose gel electrophoresis of EcoRI and PstI restriction fragments, respectively. The EcoRI family is composed of a monomeric unit of 196 bp (64.3% A-T rich) DNA sequence, representing about 120,000 copies per haploid genome. The presence of frequent intermediate-size satellite variants and an internal direct repetition of 61 bp in the EcoRI repetitive main monomer suggest that the evolution of this satellite proceeded by unequal crossing-over, occurring both within and between the 196 bp unit. Another highly repetitive sequence, defined by digestion of genomic DNA with PstI, has a more complex unit of 1.2 kb with about 70,000 copies per haploid genome. In situ digestion of M. goudoti chromosomes with restriction enzymes shows a non-specific chromosome DNA extraction from pericentromeric positions with EcoRI and chromosome specific extraction of DNA with PstI and HinfI. This is discussed in relation to the chromosomal location of both satellites.