Biogenesis of surface domains in fly photoreceptor cells: Fine-structural analysis of the plasma membrane and immunolocalization of Na+,K+ ATPase and ?-spectrin during cell differentiation

Abstract

Electron microscopic examination of pupal and adult blowfly (Calliphora erythrocephala) retina provides novel details on the biogenesis of the photoreceptor surface, particularly regarding the development of the microvillar rhabdomere and associated structures, such as the submicrovillar endoplasmic reticulum. Localization of the Na+, K(+)-ATPase on the surface of developing photoreceptors has also been examined by immunofluorescence confocal microscopy and immunogold electron microscopy. Na+, K(+)-ATPase has a nonpolarized distribution in midpupal photoreceptors that are determined by fate but that are not yet completely differentiated. Large amounts of Na+, K(+)-ATPase are synthesized and delivered to the cell surface throughout the second half of pupal life. At certain time points in late pupal development, specific membrane domains become cleared of Na+, K(+)-ATPase in the photoreceptors R1-R6. However, the distribution of Na+, K(+)-ATPase remains nonpolarized in R7/R8, even after eclosion. Because the membrane-associated cytoskeleton plays a direct role in the establishment and maintenance of membrane domains in a variety of systems, it is of interest to study the distribution of alpha-spectrin and its possible association with Na+, K(+)-ATPase. The localization of alpha-spectrin resembles the distribution pattern of Na+, K(+)-ATPase in midpupal and adult photoreceptors. However, changes in Na+, K(+)-ATPase localization in late pupal photoreceptors precede the redistribution of alpha-spectrin by several days. Biochemical studies of cellular membranes demonstrate further that Na+, K(+)-ATPase can be solubilized by Triton X-100, although alpha-spectrin remains in a macromolecular complex. These results indicate that the development and the maintenance of the polarized Na+, K(+)-ATPase distribution in blowfly photoreceptors are not tightly coupled to alpha-spectrin.

Metallothionein 2 and Heat Shock Protein 72 Protect Allolobophora chlorotica from Cadmium But Not Nickel or Copper Exposure: Body Malformation and Coelomocyte Functioning

“…Coelomocytes from individuals earthworms were used for cytospin preparations as described previously (Homa et al 2005 ). For cross-section preparations, segments posterior to the clitellum were fixed for 4 h in 2 % paraformaldehyde dissolved in PBS and then washed for 1 h in 12 % saccharose, and overnight in 25 % saccharose (both dissolved in PBS) (Baumann 1997 ). Subsequently, tissues were frozen in liquid nitrogen and sectioned (7 µm) on a cryostat (Shandon OT, Astmoor, Runcorn, Cheshire, UK), fixed with solution of 70 % cold ethanol, and stored as frozen samples (−20 °C) until further analyses.…”