The Balbiani body and generation of early asymmetry in the oocyte of a tiger beetle

The developmental changes within the Balbiani body in previtellogenic and early vitellogenic oocytes of a tiger beetle, Pseudoxycheila angustata, are described. Our study showed that the Balbiani body forms in a juxtanuclear position in previtellogenic oocytes. Subsequently, it disperses within the ooplasm while multivesicular bodies, a prominent component of the Balbiani body in this species, segregate out and are targeted to the posterior pole of the oocyte. We demonstrated that the Balbiani body is a temporary site of organelle accumulation and sorting and it is involved in the creation of an early polarity during oogenesis. Our data suggest that the multivesicular bodies, initially associated with the Balbiani body, may ultimately contribute to the formation of the pole plasm (oosome). Our study is the first description of the presence of the Balbiani body in oocytes of an insect with a meroistic ovary and only the second known example of the Balbiani body in insects in general. In addition, we showed, for the first time, that the components of Balbiani body participate in the formation of the pole plasm in insects. Interestingly, the oocytes of a European species of tiger beetles do not develop the Balbiani body. We discuss the developmental and evolutionary aspects of this finding.