In insects the embryo development occurs totally disconnected from maternal organism. Thus, the presence of all nutritive reserve inside the egg is essential for embryo nourishment. Reserve (yolk) proteins are mainly stored into organelles called yolk granules (YG). Yolk proteins degradation occurs by activation of acid hydrolases also stored within YGs. To allow hydrolases activation, the YGs undergo a process of acidification mediated by proton pumps. It is generally believed that YG population is not homogeneous since the vesicles can vary in their macromolecule contents and can be fractionated. Thus, fusion of YGs would be an attractive model of macromolecule transfer between different compartments inside the egg, possibly modulating the yolk degradation during embryogenesis. We described the YG fusion mechanisms during early embryogenesis of Rhodnius prolixus. we showed that eggs with 0 and 3 days contained  a differential size pattern of YGs in which day 3 contain a greater amount of large YG (LYG). Day 3 eggs also contain the highest [Ca²⁺] found in eggs from early embryogenesis of this insect. In vitro YGs treatment with the [Ca²⁺] found on day 3 eggs resulted in LYG appearance, as observed in vivo. We confirmed that LYG formation was the resulted of calcium dependent membrane fusion, by observations of fluorescent membrane dye transfer from previously labeled small YGs (SYG) to larger ones only in the presence of calcium. LYG and SYG were fractionated and both fractions were showed to contain the vitellins.  Results showed that SYG contain the higher levels of Acid Phosphatase and H⁺PPase activities during day 0, however LYG acquire greater activity levels of these enzymes during day 3, indicative of macromolecule transfer by membrane fusion events. In addition, we showed that YGs incubation in the presence of calcium facilitates the vitellins degradation in vitro, evidencing that YGs fusion events take part on yolk degradation probably allowing the meeting of the yolk mobilization machinery. We showed that R. prolixus YGs undergo calcium regulated membrane fusion events and this process is important for yolk degradation during early embryogenesis of Rhodnius prolixus.

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