Somatic breakpoints, distribution of repetitive DNA and non-LTR retrotransposon insertion sites in the chromosomes of Chironomus piger Strenzke (Diptera, Chironomidae)

Abstract

Structural aberrations, their frequency and distribution as well as distribution of the tandem repetitive minisatellite DNA clusters of Alu and Hinf elements and two retroelements, the LINE NLRCth1 and the SINE CTRT1, were analyzed in the genome of the chironomid C. piger Strenzke larvae from a Bulgarian population. A consistent somatic variability in the structure of the polytene chromosomes was detected, showing that the C. piger genome is more actively rearranging than supposed before. Breakpoints were concentrated in proximal parts of chromosomes significantly more often than in distal parts. By FISH analysis we could detect only one locus containing Alu elements and 38 Hinf cluster loci which appear to be dispersed equally all over the chromosomes. The retrotransposons NLRCth1 and CTRT1 are present only in a few loci, but highly variant among different individuals. The mean number of NLRCth1 sites per individual was 18.4 +/- 2.09 and of CTRT1 was 54.8 +/- 8.42. A third of breakpoint locations were close to or coincide with a locus occupied by a retroelement (either NLRCth1 or CTRT1). Nineteen percent of breakpoints coincided with Hinf repetitive DNA elements. Some breakpoints were identical in the two sibling species C. piger and C. riparius Meigen (syn.: C. thummi thummi) and are considered as conserved hot spots of chromosome breakage.

Chironomids (Diptera) and their salivary gland chromosomes as indicators of trace-metal genotoxicity

“…Aberrations are considered inherited when they affect all cells in both salivary glands of the same individual. Generally they occur at low (∼1%) frequencies in C. riparius and C. piger (Michailova et al 1996;Sella et al 2004;Michailova et al 2009a) or at >1% frequencies in C. plumosus (Butler et al 1999;Gunderina et al 1999). Inherited aberrations can result either from an aberration that occurred in the zygote or from the heritage of the parents.…”

“…In C. riparius and C. piger, the breakpoints of chromosomal rearrangements are not randomly distributed. They are accumulated in specific sites in the genome containing repetitive DNA clusters (Bovero et al 2002;Michailova et al 2009a). Bovero et al (2002) defined as "common" breakpoints those cytological points where a breakage was observed at least twice in larvae of the same or of different populations.…”

“…To study the genotoxic effect of trace-metal-polluted sediments, samples of the Chironomid species listed below were collected from sediments of different polluted water basins in a wide variety of European countries-Bulgaria, Italy, Russia, Poland, Finland and the UK (Michailova et al 1996(Michailova et al , 1998(Michailova et al , 2009aMichailova & Mettinen 2000;Ilkova 2004;Petrova et al 2004). There are no available concentration thresholds that officially define a sediment as polluted by a given trace metal.…”

“…This species has the same chromosome set and chromosome morphology as the phylogenetically younger C. riparius, which is "homosequential" -that is, with the same set-and chromosome-banding pattern. It can be distinguished from C. riparius in two ways: by the cytogenetic location of constitutive heterochromatin (Michailova et al 2009a) and by the number and location of the minisatellite clusters Alu and Hinf Michailova et al 2009a). So far, only the population of C. piger from the Kokalyane (Bulgaria) station was studied.…”

The effect of long-term contamination by heavy metals on community and genome alterations of Chironomidae (Diptera) in a stream with mine drainage water (southern Poland)

“…The chromosome set is 2n = 8. It is a species homosequental to C. riparius (both species have the same band pattern along the polytene chromosomes) and can be distinguished by the appearance and localization of heterochromatin and repetitive DNA elements (Keyl 1965, Michailova et al 2009). …”