Meiotic chromosome pairing and synaptonemal complex transformation in Culex pipiens oocytes.
The synaptonemal complexes of the oocytes of the mosquito Culex pipiens quinquefasciatus have been reconstructed from serial sections. A diffuse structure, probably a chromocenter composed of centromeric heterochromatin, was present during pachytene. As no synaptonemal complexes were visible inside the chromocenter the continuity of the 2 arms of a bivalent was lost. The telomeric ends were clustered on a small area of the nuclear membrane in a bouquet arrangement; they were associated in pairs, and sometimes joined through a special structure. One pair was composed of the 2 telomeres of the shortest bivalent and a ring configuration was thus formed. The other 2 chromosomes may form one or two rings. During a short transitional stage, after the disappearence of the synaptonemal complexes, several thousand annuli, 1200-1500 A in diameter, were present in the nuclei. The annuli disappeared as material originating mainly from the transverse filaments of the synaptonemal complexes formed a "capsule" around the chromosomes during diplotene.
D000818:Animals; D002875:Chromosomes / Q000502:physiology*; D003465:Culex / Q000235:genetics*; D005260:Female; D008540:Meiosis; D008854:Microscopy, Electron; D009865:Oocytes / Q000648:ultrastructure*; D010063:Ovum / Q000648:ultrastructure*