CENTROMERE AND TELOMERE MOVEMENTS DURING EARLY MEIOTIC PROPHASE OF MOUSE AND MAN ARE ASSOCIATED WITH THE ONSET OF CHROMOSOME-PAIRING

The preconditions and early steps of meiotic chromosome pairing were s tudied by fluorescence in situ hybridization (FISH) with chromosome-sp ecific DNA probes to mouse and human testis tissue sections. Premeioti c pairing of homologous chromosomes was not detected in spermatogonia of the two species. FISH with centromere- and telomere-specific DNA pr obes in combination with immunostaining (IS) of synaptonemal complex ( SC) proteins to testis sections of prepuberal mice at days 4-12 post p artum was performed to study sequentially the meiotic pairing process, Movements of centromeres and then telomeres to the nuclear envelope, and of telomeres along the nuclear envelope leading to the formation o f a chromosomal bouquet were detected during mouse prophase. At the bo uquet stage, pairing of a mouse chromosome-8-specific probe was observ ed. SC-IS and simultaneous telomere FISH revealed that axial element p roteins appear as large aggregates in mouse meiocytes when telomeres a re attached to the nuclear envelope, Axial element formation initiates during tight telomere clustering and transverse filament-IS indicated the initiation of synapsis during this stage. Comparison of telomere and centromere distribution patterns of mouse and human meiocytes reve aled movements of centromeres and then telomeres to the nuclear envelo pe and subsequent bouquet formation as conserved motifs of the pairing process. Chromosome painting in human spermatogonia revealed compacte d, largely mutually exclusive chromosome territories, The territories developed into long, thin threads at the onset of meiotic prophase. Ba sed on these results a unified model of the pairing process is propose d.