Genome-Wide Analysis and Hormone Regulation of Chitin Deacetylases in Silkworm

Abstract

Chitin deacetylases (CDAs) are a group of enzymes involved in chitin metabolism in insects; they play a critical role in molting, pupation, and the modification of chitin. In this study, we identified several CDAs in the silkworm, Bombyx mori (BmCDA), and investigated the effect of various hormones on their expression in B. mori larvae and embryo cell lines (BmE). Eight genes encoding BmCDAs were identified in the silkworm genome. They showed different expression patterns in different tissues, and were classified into three types based on where they were expressed: the exoskeleton, digestive organs, and genital organs. Moreover, we found that some BmCDAs showed upregulated expression during the molting period, especially during the fourth molting period in larvae. We also verified that the expression of BmCDA1–6 was upregulated by treatment with 20-hydroxyecdysone not only in larvae, but also in BmE cells. Interestingly, juvenile hormone analog treatment also upregulated the expression of some BmCDAs. The overexpression of several transcription factors revealed that the POU transcription factor POUM2 may play a major role in the regulation of BmCDA expression. Finally, the silencing of BmCDA1 and BmCDA2 did not lead to abnormal phenotypes or death, but may have led to delays in silkworm pupation. These results provide important information about lepidopteran insects in terms of chitin deacetylases and the regulation of their expression.

Role of Chitin Deacetylase 1 in the Molting and Metamorphosis of the Cigarette Beetle Lasioderma serricorne

“…In the pharate appendages of T. castaneum adults, TcCDA1-specific in situ hybridization showed a strong signal in the epidermal cells [13]. In the present study, LsCDA1 was predominantly expressed in the integument at the larval stages, which is consistent with the expression of NlCDA1, NlCDA2, and NlCDA4 from N. lugens [10], HcCDA2 from H. cunea [24], and BmCDA1 and BmCDA2 from B. mori [25]. We speculated that these CDAs are responsible for chitin metabolism in the integument and are crucial for insect molting.…”

“…In S. paniceum [14] and H. vitessoides [27], exposure to 20E could activate the expression of CDA genes at various times. Substantial upregulation of six BmCDAs (BmCDA1-BmCDA6) by 20E was observed not only in the larval cuticles and midguts, but also in embryo cell lines of B. mori [25]. These results strongly suggest that CDAs are important 20E late-responsive genes.…”

“…The silencing of NlCDA1, NlCDA2, and NlCDA4 caused molting failure and high mortality, while nonviable phenotypes were found after injection with double-stranded RNA (dsRNA) for NlCDA3 [10]. Similar molting defects were observed after RNAi of CDA genes in many insect species, including Stegobium paniceum [14], Leptinotarsa decemlineata [15,16], Locusta migratoria [19], Choristoneura fumiferana [22], Hyphantria cunea [24], Bombyx mori [25], and Heortia vitessoides [27]. In Drosophila melanogaster, mutations of DmCDA1 (Serpentine) and DmCDA2 (vermiform) led to limited tracheal elongation and affected the formation of the larval cuticle [20,28,29].…”

“…Actually, the results were not always in accordance with those of previous studies. For example, the injection of dsRNAs of BmCDA1 and BmCDA2 in the larvae of B. mori did not reveal any morphological abnormalities, but rather led to delayed pupation times [25]. Therefore, we proposed that the high expression of CDAs in the integument might be associated with additional physiological functions.…”

“…The first cDNA encoding chitin deacetylase-like protein was cloned from the cabbage looper Trichopusia ni [12]. Since then, hundreds of CDA genes have been identified in numerous insect species, including Coleoptera [13][14][15][16], Hemiptera [10], Hymenoptera [17], Orthoptera [18,19], Diptera [20,21], Lepidoptera [7,[22][23][24][25], and Isoptera [26]. Based on sequence similarity and domain organization, insect CDAs have been divided into five groups (group I−V) [17].…”