Calreticulin expression levels and endoplasmic reticulum during late oogenesis and early embryogenesis of Rhodnius prolixus Stahl.

This study reports the cloning, expression analysis and localization of calreticulin (CRT) in the endoplasmic reticulum (ER) during late oogenesis and early embryogenesis of the insect Rhodnius prolixus. CRT was cloned and sequenced from cDNA extracted from unfertilized eggs. Real-time PCR showed that CRT expression remains at lower levels during late oogenesis when compared to vitellogenic oocytes or day 0 laid fertilized eggs. Immunofluorescence microscopy showed that this protein is located in the periphery of the egg, in a differential peripheral ooplasm surrounding the yolk-rich internal ooplasm, only identified by transmission electron microscopy (TEM) of thin sections. Using immunogold electron microscopy, the ER ultrastructure (CRT labeled) was identified in the peripheral ooplasm as dispersed lamellae, randomly distributed in the peripheral ooplasm. No massive alterations of ER ultrastructure were found before or right after (30 min) fertilization, but an increase in CRT expression levels and assembly of typical rough ER (parallel cisternae with associated ribosomes) were observed 18-24 h after oviposition. The lack of ER assembly at fertilization and the later formation of rough ER together with the increase in CRT expression levels, suggest that the major functions of ER might be of great importance during the early events of development. The possible involvement of ER in the early steps of embryogenesis will be discussed.