A calsequestrin-like protein in the endoplasmic reticulum of the sea urchin: localization and dynamics in the egg and first cell cycle embryo.

Abstract

Abstract. Using an antiserum produced against a purified calsequestrin-like (CSL) protein from a microsomal fraction of sea urchin eggs, we performed light and electron microscopic immunocytochemical localizations on sea urchin eggs and embryos in the first cell cycle. The sea urchin CSL protein has been found to bind Ca ++ similarly to calsequestrin, the wellcharacterized Ca ++ storage protein in the sarcoplasmic reticulum of muscle cells. In semi-thin frozen sections of unfertilized eggs, immunofluorescent staining revealed a tubuloreticular network throughout the cytoplasm. Staining of isolated egg cortices with the CSL protein antiserum showed the presence of a submembranous polygonal, tubular network similar to ER network patterns seen in other cells and in egg cortices treated with the membrane staining dye DilC~6 [3]. In frozen sections of embryos during interphase of the first cell cycle, a cytoplasmic network similar to that of the unfertilized egg was present. During mitosis, we observed a dramatic concentration of the antibody staining within the asters of the mitotic apparatus where ER is known to aggregate. Electron microscopic localization on unfertilized eggs using peroxidase-labeled secondary antibody demonstrated the presence of the CSL protein within the luminal compartment of ER-like tubules. Finally, in frozen sections of centrifugally stratified eggs, the immunofluorescent staining concentrated in the clear zone: a layer highly enriched in ER and thought to be the site of calcium release upon fertilization. This localization of a CSL protein within the ER of the egg provides evidence for the ability of this organelle to serve a Ca ++ storage role in the regulation of intracellular Ca ++ in nonmuscle cells in general, and in the regulation of fertilization and cell division in sea urchin eggs in particular.

Demonstration of calcium uptake and release by sea urchin egg cortical endoplasmic reticulum.

“…However, an important issue that has not been resolved by the above isotope studies is the identity of the membrane compartments that sequester and release calcium . Several organelles are present on the sea urchin cortex, including cortical granules (Vacquier, 1975), pigmented and acidic vesicles (Sardet, 1984), and the ER (Sardet, 1984;Chandler, 1984) .Recently, a calsequestrin-like protein has been isolated from sea urchin eggs (Oberdorf et al, 1988), and an antibody to this protein labels the cortical ER (Henson et al, 1989) . In striated muscle, calsequestrin is a low affinity, high capacity calcium binding protein; the presence of a similar calcium binding protein in the ER of sea urchin eggs suggests that the ER is capable of sequestering calcium, but direct evidence for calcium uptake and release from the ER is lacking.…”

“…Recently, a calsequestrin-like protein has been isolated from sea urchin eggs (Oberdorf et al, 1988), and an antibody to this protein labels the cortical ER (Henson et al, 1989) . In striated muscle, calsequestrin is a low affinity, high capacity calcium binding protein; the presence of a similar calcium binding protein in the ER of sea urchin eggs suggests that the ER is capable of sequestering calcium, but direct evidence for calcium uptake and release from the ER is lacking.…”

Polarity and reorganization of the endoplasmic reticulum during fertilization and ooplasmic segregation in the ascidian egg.

“…Most work has concentrated on ER in the peripheral layer of the egg, the cortex. The cortical ER forms a two-dimensional network parallel to the plasma membrane with connections to the internal ER network (Campanella and Andreucetti, 1977;Sardet, 1984;Luttmer and Longo, 1985;Sardet and Chang, 1987;Henson et al, 1989;Speksnijder et al, 1989a;Houliston and Elinson, 1991). In sea urchin and ascidian eggs, this cortical ER is capable of calcium uptake and release and contains a high-capacity, low-affinity calciumbinding protein as well as a high concentration of calcium (Oberdorf et al, 1986;Payan et al, 1986;Oberdorf et al,animal hemisphere, and to the decreased velocity of the calcium wave at fertilization in the vegetal hemisphere (Kline and Nuccitelli, 1985;Busa and Nuccitelli, 1985).…”

Calcium Mobilization via Intracellular Ion Channels, Store Organization and Mitochondria in Smooth Muscle

“…Fertilization leads to a reorganization of the store, measured as a slowing of the diffusion of membrane probes and luminal proteins, in sea urchin eggs [55,56]. In mitosis, significant Ca 2+ store changes also occur, which include the structure itself fragmenting into subcompartments [57,58].…”