Polyphosphate polymers during early embryogenesis of Periplaneta americana.

Inorganic polyphosphates (PolyP) are linear polymers of phosphate (Pi) residues linked by high-energy phosphoanhydride bonds. Despite a wide distribution, their role during insect embryogenesis has not been examined so far. In this study, we show the mobilization of PolyP polymers during the embryogenesis of the cockroach Periplaneta americana. PolyP was detected by enzymatic and fluorimetric assays and found to accumulate in two main sizes by agarose gel electrophoresis. Confocal microscopy showed their presence in small vesicles. In addition, X-ray microanalysis of small vesicles showed considerable amounts of calcium, sodium and magnesium, suggesting an association of PolyP with these elements. Variations of the free Ca+2, Pi and PolyP levels were observed during the first days of embryogenesis. Our results are consistent with the hypothesis that phosphate ions modulate PolyP variation and that PolyP hydrolysis result in increasing free Ca+2 levels. This is the first investigation of PolyP metabolism during embryogenesis of an insect and might shed light on the mechanisms involving Pi storage and homeostasis during this period. We suggest that PolyP, mainly stored in small vesicles, might be involved in the functional control of Ca+2 and Pi homeostasis during early embryogenesis of P. Americana.

Interplay between acid phosphatase and cysteine proteases in mediating vitellin degradation during early embryogenesis of Periplaneta americana.

In this work, we characterized the activities of two classes of proteases and AcP during early embryogenesis of Periplaneta americana. AcP activity was first detected at day 6 and reached a maximum level at day 10 of development. Using phosphoamino acids, phosphatase activity was shown to be directed only against phosphotyrosine at day 6 while at day 10 it was also active against phosphoserine. In parallel, two classes of proteases were detected and located within yolk granules: a clan CA-cysteine protease, which was inhibited by E-64, insensitive to CA 074 and activated by acidic pH at day 3; and a neutral serine protease, which was inhibited by aprotinin at day 6. Assays of vitellin (Vt) degradation evidenced that incubations at neutral pH induced slight proteolysis, while the incubations at acidic pH did not result in Vt degradation. However, pre-incubations of Vt with AcP increased the levels of Vt acidic proteolysis and this could be inhibited by the addition of phosphatase inhibitors. On the other hand, the same pre-incubations showed no effects on the profile of degradation at neutral pH. We propose that AcP and cysteine protease cooperate to assure Vt breakdown during early embryogenesis of P. americana.

Calcium-regulated fusion of yolk granules during early embryogenesis of Periplaneta americana.

This work reported membrane fusion of yolk granules (YGs) during early embryogenesis of the insect Periplaneta americana (P. americana). We showed that eggs from Day 5 of embryogenesis possess a greater amount of enlarged YGs in comparison with Day 1. Day 5 is also the period when the largest amount of free calcium is found (approximately 17 mM) within the oothecae from early embryogenesis. Treatment of Day 1-YGs fraction with 17 mM Ca2+ resulted in a YG size pattern very similar to the one observed in Day 5 eggs, where enlarged YGs were formed. YG membrane fusion was observed by fluorescent membrane dye transfer from previously labeled small YGs to larger ones and was also visualized by electron microscopy. We also showed that the small "in fusion" YGs seemed to be acidic, suggesting that acidification is correlated with YG membrane fusion. Hence, it was shown that YGs are capable of membrane fusion in a calcium-dependent manner and this process probably occurs in vivo during early embryogenesis of P. americana.

[Parasitism in the oothecae of Periplaneta americana (Linnaeus)]. / Parasitismo en ootecas de Periplaneta americana (Linnaeus).

Parasitism present in others of Periplaneta americana in 3 municipalities of Havana City was observed, and it was detected that Tetrastichus hagenowii (Ratz.) attained significant levels of parasitism for an average value of 21.5% in the oothecae revised. Their presence in locations where different pesticides are used and their biological characteristics give them the probability of being an efficient bioregulator of cockroaches.