eghbx2, a homeobox gene involved in the maturation of calcified structures in Echinococcus granulosus

• Echinococcus granulosus EgHbx2 is a homeodomain protein with high homology to Drosphila NK3/bagpipe.
• EgHbx2 is expressed in the nucleus of the cell associated to the calcareous corpuscle.
• We report that calcareous corpuscle-associated cell undergoes an apoptotic process.
• We show EgHbx2 expression co-localizes with the apoptotic signals, according to corpuscles calcareous maturation.

Several homeobox-containing genes involved in the regulation of developmental events during the Echinococcus granulosus life cycle have been described. Here, we report a cellular and molecular study focused on the expression of eghbx2 in E. granulosus protoescoleces. The deduced eghbx2 homeodomain shares a significant homology with those grouped in the “NK2 family” within the NK subclass of homeoproteins and is most homologous to NK3/bagpipe. However, the role of EgHbx2 in the biology of these organisms has not yet been established. In this work, we show that eghbx2 mRNA and the corresponding protein localize in cells associated with calcareous corpuscles. Western blotting of protoscoleces revealed a single protein with a MW of approximately 46 kDa present in the nuclear extract. Immunocytochemistry analyses indicated that Eghbx2 localizes to the nucleus of cells surrounding the calcareous corpuscles. Furthermore, when the calcareous corpuscle reaches maturity, the associated cell undergoes an apoptotic process, as visualized by TEM and TUNEL studies while EgHbx2 expression co-localized with TUNEL signals. Our results lead to the conclusion that eghbx2 encodes a transcription factor that is specifically expressed in cells associated with the calcareous corpuscles. Moreover, its expression clearly showed a spatial–temporal correlation with apoptotic events related to the maturation of calcified structures.