Hemocyanin is essential for oxygen transport in early embryo of locust

The adequate supply of oxygen is critical for the embryonic development in insects. However, oxygen transport in embryo when the tracheal system is not fully developed remains elusive. Herein, we investigated the relationships between hemocyanin and tracheal development in locust embryo. The results showed that hemocyanin expression and tracheal development display a seesaw pattern during the process of embryonic development (i.e., the two show an inverse relationship: as the tracheal system gradually matures, the expression level of hemocyanin gradually decreases). The hemocyanin proteins, Hemocyanin subunits I (Hc1) and II (Hc2), possess oxygen-binding capabilities and their expression positively respond to the hypoxia in locust embryo. RNA interference (RNAi)-mediated silencing of Hc1 and Hc2 genes in the early embryo leads to hypoxia-induced malformations and mortality, thereby underscoring their essential function in embryonic oxygen transport. Once tracheal system developed, the hemocyanin gene expression rapidly declined. Intriguingly, the genes involved in tracheal system development was knockdown by RNAi, the higher expression of hemocyanin is prolonged by 1-2 d extending oxygen transport in early embryo. The tracheal system functions earlier in locust embryo than that we expected. Therefore, the hemocyanin is pivotal to transfer oxygen in early embryo of locusts. Our findings reveal that the mechanism of hemocyanin function in oxygen transport before tracheal system development in locust embryo, and provide an insight into hemocyanin function in insects.