IMMATURE ERYTHROID-CELLS WITH NOVEL MORPHOLOGY AND CYTOSKELETAL ORGANIZATION IN ADULT XENOPUS

Nucleated erythrocytes of non-mammalian vertebrates are a useful model system for studying the correlation between changes in cell shape and cytoskeletal organization during cellular morphogenesis. They are bel ieved to transform from spheres to flattened discs to ellipsoids. Our previous work on developing erythroblasts suggested that pointed cells containing incomplete, pointed marginal bands (MBs) of microtubules m ight be intermediate stages in the larval axolotl. To test whether the occurrence of such pointed cells was characteristic of amphibian eryt hrogenesis, we have utilized phenylhydrazine (PHZ)-induced anemia in a dult Xenopus. In this system, circulating erythrocytes are destroyed a nd replaced by erythroblasts that differentiate in the blood, making t hem experimentally accessible. Thus, we followed the time-course of mo rphological and cytoskeletal changes in the new erythroid population d uring recovery. During days similar to 7-9 post-PHZ, pointed cells did indeed begin to appear, as did spherical and discoidal cells. The per centage of pointed cells peaked at days similar to 11-13 in different animals, subsequently declining as the percentage of elliptical cells increased. Since degenerating ''old'' erythrocytes were still present when pointed cells appeared, we tested directly whether pointed ones w ere ''old'' or ''new'' cells. Blood was removed via the dorsal tarsus vein, and the erythrocytes washed, fluorescently tagged, and re-inject ed. In different animals, similar to 2-8% of circulating erythrocytes were labeled. Subsequent to induction of anemia in these frogs, time-c ourse sampling showed that no pointed cells were labeled, identifying them as ''new'' cells. Use of propidium iodide revealed large nuclei a nd cytoplasmic staining indicative of immaturity, and video-enhanced p hase contrast and anti-tubulin immunofluorescence showed that the poin ted cells contained pointed MBs. The results show that pointed cells, containing incomplete, pointed MBs are a consistent feature of amphibi an erythrogenesis. These cells may represent intermediate stages in th e formation of elliptical erythrocytes.