The cellular program for the formation and dissolution of the synaptonemal complex in Coprinus

Abstract

Inhibition of protein synthesis by cycloheximide on processes in meiosis was used to probe the cellular program for the formation and dissolution of the synaptonemal complex (SC) in the synchronous meiotic system of Coprinus cinereus. The pathway for the synthesis and assembly of the synaptonemal complex is proposed to be as follows: (1) synthesis and assembly of lateral components on the chromosomes; (2) synthesis and assembly of the central components in the nucleolus; (3) the lateral components of the homologous chromosomes are brought together to pair when the homologous pairing occurs at zygotene; (4) the transport of the central components from the nucleolus to join the paired lateral components and thus complete the synaptonemal complex. Continued protein synthesis is required for all steps. Step (1) is nearly complete 2 h after the onset of karyogamy, because continued assembly is possible in the presence of cycloheximide. The transition point for step (2) is 4 h after the onset of karyogamy, as inhibition at this point results in accumulation of central components in the nucleolar dense body. The paired lateral components of step (3) are deprived of the central component. The transition point for step (4) is 5 h after the onset of karyogamy, for inhibition at this point no longer prevents transport. Two steps are proposed for dissociation and dissolution of the SC at the end of pachytene. Protein synthesis is required for the dissolution of SC. Inhibition at this point causes accumulation of polycomplexes. Mutations in various organisms from the literature relating to the SC support the validity of the proposed pathway.