Identification of all pachytene bivalents in the common shrew using DAPI-staining of synaptonemal complex spreads

Abstract

A major problem in studies of synaptonemal complexes (SC) is the difficulty in distinguishing individual chromosomes. This problem can be solved combining SC immunostaining with FISH of chromosome-specific sequences. However, this procedure is expensive, time-consuming and applicable only to a very limited number of species. In this paper we show how a combination of SC immunostaining and DAPI staining can allow identification of all chromosome arms in surface-spreads of the SC of the common shrew (Sorex araneus L.). Enhancement of brightness and contrast of the images with photo editing software allowed us to reveal clear DAPI-positive and negative bands with relative sizes and positions similar to DAPI landmarks on mitotic metaphase chromosomes. Using FISH with DNA probes prepared from chromosome arms m and n we demonstrated correct recognition of the chromosomes mp and hn on the basis of their DAPI pattern. We show that the approach we describe here may be applied to other species and can provide an important tool for identification of individual bivalents in pachytene surface-spreads.

Recombination Map of the Common Shrew,Sorex araneus(Eulipotyphla, Mammalia)

“…Suppression of recombination in the pericentromeric area of the mouse chromosomes has been interpreted as an effect of the blocks of centromeric heterochromatin that reside there (Froenicke et al 2002). In the common shrew there is only a very small amount of centromeric C-heterochromatin (Schmid et al 1982;Belonogova et al 2006) and it appears less likely that this causes the recombination suppression.…”

“…The number of cells studied for each karyotype is listed in Table 1. Each chromosome arm was identified by its specific DAPI pattern according to Belonogova et al (2006). The centromere position for each SC was identified by an ANA-C focus.…”

“…The efficiency of MLH1 mapping depends crucially on reliable chromosome identification for each bivalent (indeed, for metacentrics, identification of the individual chromosome arms). A characteristic feature of the common shrew is the ease in which DAPI patterns along chromosomes can be revealed in SC spreads (Belonogova et al 2006). 2.…”

Chromosome Synapsis and Recombination in Male Hybrids between Two Chromosome Races of the Common Shrew (Sorex araneus L., Soricidae, Eulipotyphla)

“…MLH1 signals were only scored if they were localised on an SC. Each chromosome arm was identified by its specific DAPI pattern, according to Belonogova et al [ 24 ] and relative size. The centromere position for each SC was identified by DAPI-banding.…”

Sex chromosomes of basal placental mammals

“…MHL1 is a DNA mismatch repair protein that localizes to the late recombination nodules in synapsed pachytene chromosomes (Plug et al 1998;Marco and Moens 2003;Lynn et al 2004). Extensive study of the distribution of MHL1 foci along meiotic chromosomes in a variety of mammals has produced information about timing and frequency of autosomal and sex chromosomal recombination (Anderson et al 1999;Froenicke et al 2002;Belonogova et al 2006).…”