[Chicken lampbrush chromosomes: transcription of tandemly repetitive DNA sequences]

The transcribed part of the genome includes both protein-coding sequences and a variety of sequences with unknown functions. Amphibian and avian lampbrush chromosomes represent a convenient experimental system for studying cell functions and the regulation of transcription of protein-noncoding DNA. Taking lumpy loops formed on chicken (Gallusgallus domesticus) chromosome 2 at the lampbrush stage as an example, we applied an approach allowing RNA sources to be identified in the lateral loops of lampbrush chromosomes. This approach involves a bioinformatic analysis of data from the chicken genome sequencing project and a high-resolution mapping of transcripts on microsurgically isolated bivalents. As a result, a novel tandemly repetitive DNA sequence, LL2R (lumpy loop 2 repeat), of approximately 440 bp in size was identified in the chicken genome, its transcripts taking part in the formation of lumpy loops with a massive RNP matrix on chromosome 2 in growing oocytes.