Expression of calcineurin in relation to the embryonic diapause process in the silkworm, Bombyx mori

Abstract

Calcineurin (CN) is a Ca²⁺/calmodulin-activated serine/threonine protein phosphatase that is essential for translating Ca²⁺ signals into changes in cell function and development. In the present study, we investigated changes in CN expression during the process of embryonic diapause in the silkworm, Bombyx mori. An immunoblot analysis showed that Bombyx eggs contained a 59-kDa catalytic A subunit (CNA), a 19-kDa regulatory B subunit (CNB), and a 27-kDa calcipressin; the CNA, CNB, and calcipressin were found to undergo differential changes between diapause and developing eggs during the diapause process. In developing eggs, protein levels of CNA and calcipressin were high during the first stages and then gradually decreased with embryonic development. However, CNB protein levels showed inverse temporal changes, with increased levels being detected during later embryonic stages of developing eggs. In diapause eggs, protein levels of CNA and calcipressin remained at relatively high levels during the first 8 days after oviposition, but CNB levels remained at low levels. CN enzymatic activity was directly determined and results showed that it remained at low levels in diapause eggs during the first 8 days after oviposition. However, in developing eggs, CN enzymatic activity sharply increased during the first several days, reached a peak during middle embryonic development, and then greatly decreased 5 or 6 days before hatching. Examination of temporal changes in mRNA expression levels of CNB also showed differences between diapause and HCl-treated eggs. These results demonstrated that protein levels of CNA, CNB, and calcipressin, transcriptional levels of CNB, and CN enzymatic activity between diapause and developing eggs are differentially regulated, and these regulated changes are likely related to the embryonic diapause process of B. mori.

Keywords: Bombyx mori; Calcineurin; Calcipressin; Diapause; Phosphatases; Signaling.