Myocyte enhancer factor 2 exerts a pivotal role in larval development in Henosepilachna vigintioctopunctata

Abstract

Myocyte enhancer factor-2 (MEF2) plays essential roles in a variety of developmental processes. Prominent amongst multiple MEF2 functions is the regulation of muscle differentiation in Drosophila melanogaster. Nevertheless, the physiological importance of MEF2 has not been explored in non-Drosophilid insect species. Here we found HvMef2 was highly expressed at the first-instar larvae, 0-day-old second- and fourth-instar larvae, pupae and adults, especially in adult muscle in a Coleopteran potato defoliator Henosepilachna vigintioctopunctata. Injection of 200, 500 or 1000 ng of dsMef2 into the third instar larvae significantly reduced the expression of HvMef2 and impaired larval-pupal-adult transition, in a dose-dependent manner. About 68 %, 77 % and 87 % of the resulting larvae arrested as stunted prepupae, which were gradually blackened and eventually died. Around 32 %, 23 % and 13 % of the HvMef2 depleted beetles formed pupae. Among these HvMef2 depleted pupae, 22 %, 16 % and 7 % became shriveled pupae until death; roughly 10 %, 7 % and 6 % emerged as malformed adults. The growth of the adult thorax muscles was repressed. The length and width of dorsal–ventral muscles were significantly reduced. Knockdown of HvMef2 at the fourth larval instar stage caused similar defects. Likewise, introduction of dsMef2 at a dose of 200, 500 or 1000 ng into pupae led to 27 %, 20 % and 11 % emergence percentages respectively, with deformed elytra and hindwings. Therefore, MEF2 plays vital roles during metamorphosis, especially in myogenic regulation network in H. vigintioctopunctata.