Acidocalcisomes as Calcium- and Polyphosphate-Storage Compartments during Embryogenesis of the Insect Rhodnius prolixus Stahl

Abstract

BackgroundThe yolk of insect eggs is a cellular domain specialized in the storage of reserve components for embryo development. The reserve macromolecules are stored in different organelles and their interactions with the embryo cells are mostly unknown. Acidocalcisomes are lysosome-related organelles characterized by their acidic nature, high electron density and large content of polyphosphate bound to several cations. In this work, we report the presence of acidocalcisome-like organelles in eggs of the insect vector Rhodnius prolixus.Methodology/Principal findingsCharacterization of the elemental composition of electron-dense vesicles by electron probe X-ray microanalysis revealed a composition similar to that previously described for acidocalcisomes. Following subcellular fractionation experiments, fractions enriched in acidocalcisomes were obtained and characterized. Immunofluorescence showed that polyphosphate polymers and the vacuolar proton translocating pyrophosphatase (V-H+-PPase, considered as a marker for acidocalcisomes) are found in the same vesicles and that these organelles are mainly localized in the egg cortex. Polyphosphate quantification showed that acidocalcisomes contain a significant amount of polyphosphate detected at day-0 eggs. Elemental analyses of the egg fractions showed that 24.5±0.65% of the egg calcium are also stored in such organelles. During embryogenesis, incubation of acidocalcisomes with acridine orange showed that these organelles are acidified at day-3 (coinciding with the period of yolk mobilization) and polyphosphate quantification showed that the levels of polyphosphate tend to decrease during early embryogenesis, being approximately 30% lower at day-3 compared to day-0 eggs.ConclusionsWe found that acidocalcisomes are present in the eggs and are the main storage compartments of polyphosphate and calcium in the egg yolk. As such components have been shown to be involved in a series of dynamic events that may control embryo growth, results reveal the potential involvement of a novel organelle in the storage and mobilization of inorganic elements to the embryo cells.

Polyphosphate Is a Novel Pro-inflammatory Regulator of Mast Cells and Is Located in Acidocalcisomes

“…This technique was used before to localize polyP in Saccharomyces cerevisiae vacuoles (28) and in acidocalcisomes of sea urchin eggs (49) and Rhodnius prolixus (50). The negative staining by DAPI used for the urea-PAGE analysis allows the discrimination among DNA, RNA, and glycosaminoglycans which do not photobleach in the time frame necessary for complete photobleaching of even nanomolar amounts of polyP, and heparin, which photobleach very slowly on exposure to UV light (32).…”

Polyphosphate: an ancient molecule that links platelets, coagulation, and inflammation

“…And finally, the isolated polyP binding domain of E coli exopolyphosphatase has been used successfully as a probe to localize polyP in yeast cells 107 and in acidocalcisomes in eggs of sea urchins 108 and insects. 109 For a variety of experiments, it would be desirable to be able to covalently attach biotin, epitope tags, dyes, fluorophores, etc, to polyP, and also to covalently immobilize polyP onto solid supports, such as magnetic beads and multiwell plates. PolyP can be immobilized onto zirconia beads via Lewis acid/base interactions, 110 a method we have used to quantify exosite II-mediated thrombin binding to immobilized polyP.…”

The origin and evolution of the acidocalcisome and its interactions with other organelles

“…Typical acidocalcisomes were recently found in the midgut of the caterpillar Anticarsia gemmatalis , although they were called spherites [37]. Acidocalcisomes have recently been described in other eukaryotes such as Eimeria acervulina , and Eimeria tenella , parasites that infect poultry flocks all over the world [38], and in the egg yolk of the insect Rhodnius prolixus [39], one of the insect vectors of T. cruzi . Mast cell granules and human basophil granules were also shown to contain polyP, calcium and an acidic pH and together with their elemental composition have the characteristics of typical acidocalcisomes [14].…”