Posttranslationally modified tubulins and microtubule organization in hemocytes of the brine shrimp, Artemia franciscana

Crustaceans possess blood cells (hemocytes) that mediate organismal defense and are analogous to vertebrate leukocytes. In order to more fully charact erize these types of cells, hemocytes of the branchiopod crustacean, Artemi a franciscana, were analyzed. The data indicate that Artemia have one type of hemocyte, ranging in morphology from compact and spherical to flat and s preading when examined in vitro. Electron microscopy revealed many cytoplas mic granules in the hemocytes and only a limited number of other membrane-b ound organelles. Centrioles and microtubules were also visible in thin sect ions of chemically fixed samples. The cytoplasm of spherical hemocytes was completely labeled by general antitubulin antibodies, but in flattened hemo cytes packing of cytoskeletal elements was less tight and individual microt ubules were observed. Probing of Western blots disclosed acetylated, tyrosi nated, and detyrosinated tubulin isoforms in hemocyte homogenates, the firs t characterization of posttranslationally modified tubulins in this cell ty pe. Acetylated tubulin was restricted to a subset of microtubules, whereas tyrosinated microtubules were displayed more abundantly. Staining obtained with antibody to detyrosinated tubulin was unusual because it was limited t o the perinuclear region of hemocytes. Incubation of blood cells with a mon oclonal antibody to gamma-tubulin yielded fluorescent dots sometimes in pai rs, a pattern characteristic of centrosomes. The findings support the concl usion that Artemia hemocytes undergo rapid morphogenesis in vitro accompani ed by extensive rearrangement of their microtubules, the latter probably in dicative of cytoskeletal changes that occur during cell movement and phagoc ytosis. Additionally, the hemocytes contain posttranslationally modified cr -tubulins and centrosome-associated gamma-tubulin, both with the potential to influence microtubule organization and function. (C) 2000 Wiley-Liss, In c.