On the positions of centromeres in chicken lampbrush chromosomes

Abstract

Using immunostaining with antibodies against cohesin subunits, we show here that cohesin-enriched structures analogous to the so-called centromere protein bodies (PB) are the characteristic of galliform lampbrush chromosomes. Their centromeric location was verified by FISH with certain DNA probes. PB-like structures were used as markers for centromere localization in chicken lampbrush chromosomes. The gap predicted to be centromeric in current chicken chromosome 3 sequence assembly was found to correspond to the non-centromeric cluster of CNM repeat on the q-arm of chromosome 3; the centromere is proposed to be placed at another position. The majority of chicken microchromosomes were found to be acrocentric, in contrast to Japanese quail microchromosomes which are biarmed. Centromere cohesin-enriched structures on chicken and quail lampbrush microchromosomes co-localize with pericentromeric CNM and BglII- repeats respectively. FISH to the nascent transcripts on chicken lampbrush chromosomes revealed numerous non-centromeric CNM clusters in addition to pericentromeric arrays. Complementary CNM transcripts from both C- and G-rich DNA strands were revealed during the lampbrush stage.

Transcription of highly repetitive tandemly organized DNA in amphibians and birds: A historical overview and modern concepts

“…The fate of transcripts is shown on example of CNM tandem repeat, whose transcription from both strands during lampbrush stage was demonstrated. 54 restricted on the long arm of chromosome I of the newt T. c. carnifex. 1,35 Transcribed tandemly repetitive sequences X132A in X. laevis were found at the terminal regions of the chromosomes.…”

“…52 CNM repeat is transcribed from both strands forming loop-specific pattern of Gand C-rich transcripts. 54 The C-rich transcripts of the CNM repeat were discovered on the lateral loops originating from the centromere chromomeres of microchromosomes and from the subterminal site of macrochromosome 3, while transcripts from opposite strand of the CNM repeat (G-rich transcripts) were detected on q-terminal regions of microchromosomes. 52,54 Chromosome-specific differences involving transcription of the PO41 and BglII-repeats were revealed.…”

“…3B). 52,54 However, it is not clear yet whether these non-coding RNAs anneal to form dsRNA. We propose a hypothesis that short regulatory RNAs originating from tandemly repetitive sequences participate in heterochromatin formation at the early stages of embryo development.…”

High-resolution mapping and transcriptional activity analysis of chicken centromere sequences on giant lampbrush chromosomes

“…Other macrochromosomes, namely GGA6 and GGA9, and most of the gene-rich microchromosomes, typical for Galliform karyotypes, contain an identical 41 bp-repeat (CNM repeat) within their centromere regions (Matzke et al 1990). CNM repeat is not centromere-specific and in addition to centromere regions localises in subtelomeric and interstitial regions of certain chicken chromosomes (Krasikova et al 2006). The centromere region of one of the small microchromosomes, GGA27, similar to centromeres of GGA5 and GGAZ, is built by non-tandemly repetitive DNA sequences (Shang et al 2010).…”

“…According to data reported by Edwards and Murray (2005), CENP-A protein is not concentrated at centromeres of Xenopus lampbrush chromosomes, and the position of a centromere can be defined by presence of centromeric repeats that are known to interact with CENP-A at other stages of the cell cycle and in other tissues. Importantly, in both avian and amphibian lampbrush chromosomes, pericentromeric compact chromomeres usually bear pairs of lateral loops, often very long, where RNA-polymerase II transcribes fragments of satellite DNA arrays (Diaz et al 1981;Baldwin and Macgregor 1985;Barsacchi-Pilone et al 1986;Solovei et al 1996;Krasikova et al 2006;Deryusheva et al 2007). At the same time, transcriptional activity of truly centromeric sequences has not been studied in detail.…”