Defective pairing and synaptonemal complex formation in a Sordaria mutant (spo44) with a translocated segment of the nucleolar organizer

Abstract

The recessive meiotic mutant spo44 of Sordaria macrospora, with 90% ascospore abortion, exhibits striking effects on recombination (67% decrease), irregular segregation of the almost unpaired homologues, and a decrease in chiasma frequency in the few cases where bivalents are formed. Three-dimensional reconstructions of ten prophase nuclei indicate that pairing, as judged by the absence of fully formed synaptonemal complexes (SC), is not achieved although lateral elements (LE) assemble. The pairing failure is attributable to defects in the alignment of homologous chromosomes. The leptotene alignment seen in the wild type before SC formation was not observed in the spo44 nuclei. Dense material, considered to be precursor of SC central elements, was found scattered among the LE in two nuclei. The behaviour of spo44 substantiates the hypothesis that chromosome matching and SC formation are separable events. - The total length of the LE in the mutant is the same as in the wild type, but due to variable numbers and length of the individual LE, homologues cannot be lined up. Light microscopic observations indicate that the irregular length and number of LE is due to extensive chromosome breakage. The wild-type function corresponding to spo44 is required for both LE integrity and chromosome matching. Reconstructions of heterozygous nuclei reveal the presence of a supernumerary nucleolar organizer in one arm of chromosome 7. It is suggested that rDNA has been inserted into a gene whose function is involved in pairing or into a controlling sequence that interacts with the pairing process.

Comparative sequence analysis of Sordaria macrospora and Neurospora crassa as a means to improve genome annotation

“…S. macrospora has also been used to analyze chromosome pairing and recombination during meiosis. This has involved extensive cytological studies as well as work on the molecular basis of meiotic events (Le Chevanton and Zickler, 1991;Thompson-Coffe et al, 1999;van Heemst et al, 1999;Zickler et al, 1985Zickler et al, , 1992.…”

Full-Length Synaptonemal Complex Grows Continuously during Meiotic Prophase in Budding Yeast

“…SC formation (synapsis) involves the multimeric assembly of coiled-coil containing proteins; the coiled-coil containing proteins that establish the SC central region interact with themselves and with chromosome axis proteins associated with each homolog in order to ultimately generate an elaborate protein lattice at the interface of lengthwise-aligned chromosomes [2], [3]. SC links initial homolog pairing with pairing maintenance by virtue of the fact that SC assembly is normally regulated such that it occurs only subsequent to homology recognition between chromosomes, whereas a fully assembled SC may be required for a normal number and distribution of crossover recombination events (which will in turn ensure the persistence of homologous associations after SC disassembly and until chromosome segregation on the meiosis I spindle) [2]–[8].…”

SUMO Localizes to the Central Element of the Synaptonemal Complex and is Essential for Meiotic Chromosome Synapsis in Saccharomyces cerevisiae

“…In order to segregate properly, chromosomes must identify and stably associate with their homologous partners. In the absence of such associations, homologs will segregate randomly with respect to one another, which can result in aneuploid daughter cells (Abbe 1881;Zickler, Lares et al 1985;Chelysheva, Gendrot et al 2007). Despite its critical importance, the molecular mechanisms that underlie stable homolog pairing during meiosis are poorly understood.…”