Evidence-based insights on Leishmania replication and cytokinesis

Background: Leishmania parasites are transmitted to humans and mammals by sand fly vectors in the form of flagellated promastigotes that propagate inside tissue macrophages in the form of aflagellate amastigotes. Majority of information on sequential development is derived from that of the kinetoplastids: trypanosomatidae; notably that of T. brucei. Objective: Investigation of ultra-morphologic events involved in Leishmania replication to provide a detailed description of the sequential processes by which Leishmania replicates its single-copy organelles Material and Methods: Leishmania promastigotes were maintained by in vitro culture, and amastigotes were attained by inoculation of laboratory out bred male Syrian hamsters with cultured promastigotes. Concentrated pellets of promastigotes and 1 mm thick tissue biopsies from infected hamsters were optimally processed for electron microscopy. Ultrathin-sections were examined and photographed by a Zeiss EM 952 electron microscope. Results: In promastigotes and amastigotes, initial amplification of subpellicular microtubules resulted in morphometric increase in size of the dividing forms. Replication of nucleus and kinetoplast was asynchronous. Kinetoplast S phase occurred before commencement of nuclear S phase. Lengthening and merging of the kinetoplast mitochondrion occurred into that of the amastigote cell and coincided with detection of the hidden basal body which started duplication of the flagellum. Separation of basal body, flagellar pocket and flagellum appeared to occur before kinetoplast division which was found to divide and separate before closed mitosis (pleuromitosis). Centrosomes were recognized in the centre of the spindle synchronously with the K-DNA lengthening. Cytokinesis progressed from the posterior pole to the anterior pole of the cell along the longitudinal axis, bisecting the cell symmetrically. Conclusion: Compiled records provided definite information on the sequential cellular cycle of the Leishmania spp. and the chronological proceedings of replication of their nucleus and kinetoplast. Replication by nuclear (karyokinesis) and cytoplasmic (cytokinesis) division machineries, documents its non-conformability with its taxonomically related trypanosomatids.