Endoplasmic reticulum stress responses in Leishmania.
The fine structure of apoptotic HeLa cells from cultures contaminated with mycoplasma in early and in advanced stages of the cell demise process differs from those so far described in apoptotic cells. The observed changes are enhanced after exposure of the cells to staurosporine. At low microscopic magnifications cells that have apparent normal cytoplasm and nuclei, actually may be harbouring cystic-like profile(s) of parasitic origin in an altered cytoplasm. The membranes of the transitional elements of the endoplasmic reticulum (TER) appear fragmented in irregular branching stripes of the smooth component of the TER (Fig. 1, white asterisks in L delimited area). The concentration of the rough endoplasmic reticulum (RER) membranes is less than in normal HeLa cells. Near to the smooth ER tubule-saccular elements lie groups of 50 nm microvesicles aside stacked, thin, various sized profiles of Golgi saccules ( ] ). The 50 nm microvesicles bud off mainly from the periphery of the stacked Golgi elements (Fig 1 thin arrow heads inside line U) and also from the extremities of smooth ER tubules (Fig. 1 small arrows). Small groups of compacted microvesicles are noted in cells still maintaining normal nuclear appearance (not shown). With the start of chromatin condensation progressively larger compact microvesicular clusters are formed. These attain sizes larger (Fig. 2) than those of the clusters of microvesicles derived from the fragmentation of Golgi saccules seen in mitotic (LUCOCQ et al., 1989; SESSO et al., 1999) and in apoptotic (SESSO et al., 1999) cells. Contemporaneously two major cytoplasmic alterations may be noted in contaminated cells namely when treated with staurosporine. Occasionally, both deformations appear in the same cell. One, is progressive cytoplasmic loss by formation at the cell periphery of blebs that separate from the inner cytoplasm (Figs. 3 and 4) or by localized detachment of sectors of the peripheral cytoplasm with various forms and sizes (not shown). In some cells, the remainder thin, cytoplasm with few mitochondria and rough ER profiles surrounds the nucleus in a ring-like form. Such small cells are noted in heavily contaminated samples. Some of the cells exhibit sectors of the cytoplasm with a reticulated appearance. Such net-like regions are composed by various sized tubular and ellipsoidal, apparently empty profiles. It is unclear if the smooth membranes that compose these regions with reticulated aspect, may have derived from the Golgi apparatus. The shape and size of the empty spaces correspond to those from villus-like formations seen free close to and emerging from the cell surface. In contaminated cells namely after staurosporine treatment the free villus like forms are seen sprouting from the cell surface and also free nearby. Spheroidal 50-100nm (thin arrow in Fig. 5) profiles with inner structure identical to that of villus-like elements are consistently proximate to the fake villi. Vestiges of what can be remnants of the villus-simile structures and/or of the parasite itself are seen in these spaces (Figs. 6 and 7). It is yet undetermined whether the early structural changes expressed by foci of assembled microvesicles at the transitional endoplasmic reticulum-Golgi interface is an exclusive type of membranal alteration preceding overt apoptosis in mycoplasma infected cells.