Localization and transcriptional activity analysis of RrS1 repeat in centromere regions of P. lessonae lampbrush chromosomes. a, c. Microphotographs with DNA/DNA (a) and DNA/(DNA+RNA) (c) FISH of RrS1 repeat to lampbrush chromosomes of P. lessonae (red). Chromosomes are counterstained with DAPI (blue). Asterisks indicate enlarged fragments of the same chromosomes with fluorescent signal of RrS1 repeat shown on panels a` and c`. d, f. Schematic drawings of chromosomal centromere regions demonstrate the distribution of visualized DNA/DNA (d) and DNA/(DNA+RNA) (f) FISH signals (red). Transcripts of RrS1 repeat are not detectable after pre-treatment with RNase A; RrS1 repeat localizes in two distinctive chromomeres in a centromere region (indicated by arrowheads) (a, a`, d). Without pre-treatment with RNase A hybridization signal is clearly revealed not only in centromere chromomeres but also in RNP-matrix of long lateral loops (indicated by arrows) extended from the centromere chromomeres (c, c`, f). Circular arrows show direction of transcription (e, f). TU – transcriptional unit. b, b`, e. Corresponding phase contrast micrographs (b, b`) and schematic drawing of a centromere region (e). Nu – extrachromosomal nucleoli. Scale bars = 10 μm.