Expression dynamics and functional characterization of the pigmented and non-diapausing egg gene ( pnd ) and pnd-2 , responsible for the initiation of embryonic diapause in the silkworm, Bombyx mori

Diapause in insects is a developmental arrest that serves as an adaptation to severe environmental conditions. In the silkworm Bombyx mori , embryonic diapause in the next generation is maternally induced by the diapause hormone (DH). However, the downstream factors responsible for initiating diapause have remained unidentified. The pnd and pnd-2 mutants produce p igmented and n on- d iapausing eggs despite intact DH signaling, indicating that the pnd and pnd-2 genes act downstream as potential initiators of diapause. Here, we analyzed their expression dynamics and functions. Expression analyses showed that pnd was strongly upregulated in diapause-destined eggs in a DH-signal-dependent manner and was suppressed by HCl treatment that prevents diapause initiation. In contrast, pnd-2 exhibited a transient expression peak independent of DH-signal and was unaffected by HCl treatment. RNAi-mediated knockdown of either gene inhibited the diapause initiation, and injection of pnd mRNA into non-diapause-destined eggs induced a diapause-like state in embryos. These findings demonstrate that pnd and pnd-2 are required downstream of the DH-signal to initiate diapause, providing key insights into the molecular mechanism underlying embryonic diapause induction in B. mori .