The Dissection of Meiotic Chromosome Movement in Mice Using an In Vivo Electroporation Technique

During meiosis, the rapid movement of telomeres along the nuclear envelope (NE) facilitates pairing/synapsis of homologous chromosomes. In mammals, the mechanical properties of chromosome movement and the cytoskeletal structures responsible for it remain poorly understood. Here, applying an in vivo electroporation (EP) technique in live mouse testis, we achieved the quick visualization of telomere, chromosome axis and microtubule organizing center (MTOC) movements. For the first time, we defined prophase sub-stages of live spermatocytes morphologically according to (GFP-)TRF1 and (GFP-)SCP3 signals. We show that rapid telomere movement and subsequent nuclear rotation persist from leptotene/zygotene to pachytene, and then decline in diplotene stage concomitant with the liberation of SUN1 from telomeres. Further, during bouquet stage, telomeres are constrained near the MTOC, resulting in the transient suppression of telomere mobility and nuclear rotation. MTs are responsible for these movements by forming cable-like structures on the NE, and, probably, by facilitating the rail-tacking movements of telomeres on the MT cables. In contrast, actin regulates the oscillatory changes in nuclear shape. Our data provide the mechanical scheme for meiotic chromosome movement throughout prophase I in mammals.