IMMUNOELECTRON MICROSCOPIC AND ULTRASTRUCTURAL STUDY OF RAT PACHYTENE SPERMATOCYTE : CHROMOSOME REPLICATION IN PRE-MEIOTIC INTERPHASE AND SYNAPTONEMAL COMPLEXES

The synaptonemal complexes (SCs), the unique organelle of the meiotic prophase nucleus, play important roles in the meiosis-specific events of homologous chromosome pairing, genetic recombination, and chromosome disjunction. Recently the SCs structure has been actively studied using immunohistochemical technique. However, it is still unknown whether nuclear skeleton in premeiotic interphase basically corresponds with SCs in meiotic prophase in spite of the resemblance of the shapes in these two structures. Therefore, I studied the meiotic prophase nucleus in rat testis after hypotonic treatment under the electron microscopy. Moreover, the male rat was infused continuously with a low dose bromodeoxyuridine (BrdU) from the tail vein, following a modified Counce-Meyer's microspreading procedure and immunogold labeling was performed in this study. The results were as following : (1) The SCs are composed of at least two different electron dense granules and chromatin fibers. These granules and fibers form a radial loop in lateral or central elements as hitherto assumed. (2) The replication patterns of autosomal chromatin were similar to those of sex chromatin. (3) Chromosome replications had a time lag between cross of SCs part and near the SCs part, indicating that SCs and nuclear skeleton is different structure organelle. These results suggest that continuous infusion of low dose BrdU is useful for DNA replication study