Most egg calmodulin is a follicle cell contribution to the cytoplasm of the Blattella germanica oocyte.
A high concentration of calmodulin (CaM) appears in mid- to late vitellogenic cockroach follicles which composes 1.5% of total protein. CaM levels during oogenesis were estimated by densitometric analysis of immunoblots using anti-Blattella germanica egg CaM antibody as a probe. CaM accumulates in the follicle throughout the yolk deposition phase maintaining its highest level of accumulation during the later 6-fold increase in oocyte volume. Evidence suggests that this later accumulated CaM is synthesized by the follicle cells and deposited in the oocyte. In vitro experiments with [35S]-met showed that the highly abundant CaM accumulating in vitellogenic follicles may not all be synthesized by the oocyte. Isolated follicle cells incorporate 13-fold more [35S]-met into CaM than the oocytes themselves but do not accumulate the product. The follicle cells are capable of producing all the CaM observed in newly ovulated eggs. No CaM is detectable in transit in the hemolymph of the female. These facts argue that CaM produced by follicle cells is the most likely source of CaM in the vitellogenic oocyte. Indirect immunofluorescent staining with anti-egg CaM demonstrated that in early- and midvitellogenic follicles CaM is localized in the cytoplasm of follicle cells and the cytoplasmic compartment surrounding yolk granules of oocytes but is excluded from yolk granules. Immunofluorescence was most intense in the cortex of the oocyte and outside the membranes of yolk granules. Transport of CaM into the cytoplasmic compartment of the oocyte is possible without invoking traditional adsorptive endocytosis.