Chromosome cores and chromatin at meiotic prophase

We review the synaptonemal complex, SC, of the synapsed homologous chromosomes at meiotic prophase in insects and mammals in terms of its formation, and the association of specific chromatin elements with the synaptonemal complexes. The focus is: (1) The SC as visualized with a variety of techniques; (2) The nature of the chromatin loops where they are associated with the SCs--the bases of the loops may be instrumental in recombinant events judging from the presence of Rad51 protein and late recombination nodules at the SCs; (3) Differences in DNA content of similarly sized loops; (4) Requirements for chromatin attachment to the chromosome cores, requirements that are apparently lacking in foreign DNA inserts; (5) Regulation of loop size by the position along the chromosome; (6) The structural correlates of recombination at the SCs--these comments are based on studies of SC structure, DNA-core protein associations, fluorescent in situ hybridization to visualize specific DNA segments, and fluorescent immunocytology to visualize the chromosome core proteins.