Synaptonemal Complexes in the Pre-cyst of Pneumocystis carinii

• Published in: The Journal of eukaryotic microbiology 2001-01, Vol.48 (s1), p.134s-134s
• Main Authors: PETERS, SARAH E., ENGLISH, KATE, RANA, AMER, AKTER, SAYMA, MALIK, SHAMAILA, WARBURTON, NICHOLAS C., DUCKETT, JEFFREY G.
• Format: Article
• Language: English
• Subjects: Animals; Lung - microbiology; Meiosis - physiology; Microscopy, Electron; Pneumocystis - growth & development; Pneumocystis - ultrastructure; Rats; Synaptonemal Complex - ultrastructure; Tissue Fixation - methods
• ISSN: 1066-5234; 1550-7408
• DOI: 10.1111/j.1550-7408.2001.tb00485.x

P. carinii from several different hosts has been examined by transmission electron microscopy. The organism exists in several forms within infected lungs: the unicellular trophozoite or trophic form, the pre-cyst, the cyst (containing eight intracystic bodies or spores) and the empty or excysted cyst. It is presumed that the trophozoite is haploid and divides by binary fission, but that it also undergoes a conjugation at the beginning of the sexual stage of its life-cycle. The pre-cyst is an intermediate stage between the trophozoite and the cyst. Following a meiotic event in the uninuclear pre-cyst, the function of this stage is the production of eight nuclei in the mature cyst. Evidence for meiosis is the presence of the synaptonemal complex, in which paired homologous chromosomes in a diploid nucleus undergo recombination. Matsumoto and Yoshida reported the presence of the synaptonemal complex in P. carinii in rat alveoli, but to date this is the only report of this structure in P. carinii. Their study also detailed the three stages of the pre-cyst: early, intermediate and late. The early pre-cyst is uninuclear and it is in this stage that synaptonemal complexes were observed. Meiosis I and II occur in the intermediate pre-cyst, producing four haploid nuclei and a post-meiotic mitosis results in the formation of eight nuclei to produce the late pre-cyst. Development of a delimiting membrane in the late pre-cyst produces the eight intracystic bodies in the mature cyst, which ruptures to release intracystic bodies as young trophozoites. We have carried out an ultrastructural study of P. carinii using a fixative which well preserved the organisms. Here we present an example of synaptonemal complexes in the early pre-cyst, confirming the earlier report of Matsumoto and Yoshida.