Intituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.
PLoS One. 2011;6(11):e27276. doi: 10.1371/journal.pone.0027276. Epub 2011 Nov 11.
The 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 FINDINGS: Characterization 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.
We 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.
昆虫卵的卵黄是一个专门用于储存胚胎发育所需储备成分的细胞区室。储备大分子储存在不同的细胞器中，它们与胚胎细胞的相互作用大多未知。液泡钙磷体是溶酶体相关的细胞器，其特点是酸性、高电子密度和大量与几种阳离子结合的多磷酸盐。在这项工作中，我们报告了在昆虫载体 Rhodnius prolixus 的卵中存在液泡钙磷体样细胞器。
方法/主要发现：通过电子探针 X 射线微分析对电子致密小泡的元素组成进行了表征，发现其组成与以前描述的液泡钙磷体相似。在进行亚细胞分级实验后，获得了富含液泡钙磷体的级分并对其进行了表征。免疫荧光显示，多磷酸盐聚合物和液泡质子转运焦磷酸酶（V-H(+)-PPase，被认为是液泡钙磷体的标志物）存在于相同的小泡中，这些细胞器主要定位于卵皮层。多磷酸盐定量显示，液泡钙磷体中含有大量的多磷酸盐，在第 0 天的卵中即可检测到。对卵级分的元素分析表明，24.5±0.65%的卵钙也储存在这些细胞器中。在胚胎发生过程中，用吖啶橙孵育液泡钙磷体显示，这些细胞器在第 3 天（与卵黄动员时期相吻合）酸化，多磷酸盐定量显示，在早期胚胎发生过程中，多磷酸盐的水平趋于下降，与第 0 天的卵相比，第 3 天的卵中多磷酸盐含量约低 30%。
我们发现液泡钙磷体存在于卵中，是卵黄中多磷酸盐和钙的主要储存室。由于这些成分已被证明参与了一系列可能控制胚胎生长的动态事件，因此研究结果表明，一种新型细胞器可能参与了无机元素向胚胎细胞的储存和动员。
