A corset function of exoskeletal ECM promotes body elongation in Drosophila

Body elongation is a general feature of development. Postembryonically, the body needs to be framed and protected by extracellular materials, such as the skeleton, the skin and the shell, which have greater strength than cells. Thus, body elongation after embryogenesis must be reconciled with those rigid extracellular materials. Here we show that the exoskeleton (cuticle) coating the Drosophila larval body has a mechanical property to expand less efficiently along the body circumference than along the anteroposterior axis. This “corset” property of the cuticle directs a change in body shape during body growth from a relatively round shape to an elongated one. Furthermore, the corset property depends on the functions of Cuticular protein 11 A and Tubby, protein components of a sub-surface layer of the larval cuticle. Thus, constructing a stretchable cuticle and supplying it with components that confer circumferential stiffness is the fly’s strategy for executing postembryonic body elongation.

RNA-seq Analysis Reveals Mitochondrial and Cuticular Protein Genes Are Associated with Phosphine Resistance in the Rusty Grain Beetle (Coleoptera:Laemophloeidae)

The rusty grain beetle, Cryptolestes ferrugineus (Stephens), is a serious pest of stored grain, which has developed high levels of resistance to phosphine. In this study, five geographically distant populations of C. ferrugineus had been collected in China, specifically in granaries where phosphine fumigant is used for pest control, and they showed a high resistance ratio up to 1,907 (LC50 = 21.0 mg/liter). Then, a reference transcriptome was constructed to use as a basis for investigating the molecular mechanisms of phosphine resistance in this species, which consisted of 47,006 unigenes with a mean length of 1,090. Subsequently, the RNA-Seq analysis of individuals from the most susceptible and resistant populations led to the identification of 54 genes that are differentially expressed. GO and KEGG analysis demonstrated that genes associated with mitochondrial and respiration functions were significantly enriched. Also, the ‘structural constituent of cuticle’ term was annotated in the GO enrichment analysis and further qRT-PCR confirmed that the expression levels of nine cuticular protein genes were significantly increased in the resistant population. In conclusion, we present here a transcriptome-wide overview of gene expression changes between resistant and susceptible populations of C. ferrugineus, and this in turn documents that mitochondria and cuticular protein genes may play together a crucial role in phosphine resistance. Further gene function analysis should enable the provision of advice to expedite resistance management decisions.

Transcription factor FTZ-F1 regulates mosquito cuticular protein CPLCG5 conferring resistance to pyrethroids in Culex pipiens pallens

Background Culex pipiens pallens poses a serious threat to human health because of its widespread distribution, high carrier capacity for several arboviruses, frequent human-biting, and growth in urban environments. Pyrethroid insecticides have been mainly used to control adult Cx. pipiens pallens during outbreaks of mosquito-borne diseases. Unfortunately, mosquitoes have developed resistance, rendering the insecticides ineffective. Cuticular resistance is the primary mechanism of pyrethroid resistance. Previously, we revealed that cuticular protein of low complexity CPLCG5 is a major cuticular protein associated with deltamethrin resistance in Cx. pipiens pallens, which is enriched in the cuticle of mosquitoes’ legs and participates in pyrethroid resistance by forming a rigid matrix. However, the regulatory mechanisms of its transcription remain unknown. Results First, qRT-PCR analysis revealed that the expression of FTZ-F1 (encoding Fushi tarazu-Factor 1) was ~ 1.8-fold higher in the deltamethrin-resistant (DR) than deltamethrin-susceptible (DS) strains at 24 h post-eclosion (PE) and ~ 2.2-fold higher in the DR strain than in the DS strain at 48 h PE. CPLCG5 and FTZ-F1 were co-expressed in the legs, indicating that they might play an essential role in the legs. Dual luciferase reporter assays and EMSA (electrophoretic mobility shift experiments) revealed that FTZ-F1 regulates the transcription of CPLCG5 by binding to the FTZ-F1 response element (− 870/− 864). Lastly, knockdown of FTZ-F1 not only affected CPLCG5 expression but also altered the cuticle thickness and structure of the legs, increasing the susceptibility of the mosquitoes to deltamethrin in vivo. Conclusions The results revealed that FTZ-F1 regulates the expression of CPLCG5 by binding to the CPLCG5 promoter region, altering cuticle thickness and structure, and increasing the susceptibility of mosquitoes to deltamethrin in vivo. This study revealed part of the mechanism of cuticular resistance, providing a deeper understanding of insecticide resistance.

Successively expressed cuticular protein genes at the prepupal stage in wing discs of Bombyx mori

Background We classified cuticular protein genes expressed at prepupal stage in wing discs of Bombyx mori into six groups according to their developmental expression and ecdysone responsiveness. Their expression pattern is suggested to be regulated by ecdysone-responsive transcription factors, whose transcripts showed resemblance with those of cuticular protein gene expression. Result Group1 and Group2 CP genes showed peak expression at stage W2. Group3 CP genes showed high expression at stage W3E and W3L and were upregulated by 20E addition, showing a peak 12 h after 20E pulse treatment. Group4 CP gene transcripts started expression from stage V5 and peaked at stage W3L. Some genes showed significant increase 4 or 6 h after 20E addition and were induced 6 h and showed a peak 18 h after the 20E pulse treatment. Group5 CP gene transcripts peaked at the same stage W3L. Some Group5 genes showed significant increase 6 h after the 20E addition, while others were not induced by the 20E addition. These different sub-groups showed different expression profiles in the feeding stage. Transcripts of this group genes were induced 12 h and showed a peak 18 h after the 20E pulse treatment. Group6 CP genes peaked at the stage P0, were not induced by the 20E addition, and showed a peak 24 h after the 20E pulse treatment. Group3, 4, 5, and 6 CP genes are suggested to be regulated by BHR4, BR-C, E74A, and βFTZ-F1, respectively. ERTFs showed different responsiveness to 20E concentration. BR-C was most and E74A was least insensitive. The addition of cycloheximide inhibited BR-C, E74A, and βFTZ-F1 expression depending on the length of treatment after ecdysone pulse treatment, which suggests that BHR4 induced BR-C, E74A, and βFTZ-F1. Conclusion Expression patterns of CPs were determined by the ecdysone-responsiveness and the related ERTFs expressed in the prepupal stage in B. mori wing discs.

Comparative transcriptomic analysis and endocuticular protein gene expression of alate adults, workers and soldiers of the termite Reticulitermes aculabialis

Background The insect cuticle is mainly composed of exocuticle and endocuticle layers that consist of a large number of structural proteins. The thickness and synthesis of the exocuticle depend on different castes that perform various functions in alates, workers and soldiers. However, it is not clear whether the soft endocuticle is involved in the division of labour in termite colonies. To reveal the structural characteristics of the endocuticle in different castes, we investigated the thickness of endocuticle layers in alates, workers and soldiers of the termite Reticulitermes aculabialis, and then we sequenced their transcriptome and detected the endocuticle protein genes. The differential expression levels of the endocuticular protein genes were confirmed in the three castes. Results We found that there was a great difference in the thickness of the endocuticle among the alates, soldiers and workers. The thickest endocuticle layers were found in the heads of the workers 7.88 ± 1.67 μm. The endocuticle layer in the head of the workers was approximately three-fold and nine-fold thicker than that in the heads of soldiers and alates, respectively. The thinnest endocuticle layers occurred in the head, thorax and abdomen of alates, which were 0.86 ± 0.15, 0.76 ± 0.24 and 0.52 ± 0.17 μm thick, respectively, and had no significant differences. A total of 43,531,650 clean sequencing reads was obtained, and 89,475 unigenes were assembled. Of the 70 identified cuticular protein genes, 10 endocuticular genes that belong to the RR-1 family were selected. qRT-PCR analysis of the five endocuticular genes (SgAbd-2, SgAbd-9, Abd-5, SgAbd-2-like and Abd-4-like) revealed that the endocuticle genes were more highly expressed in workers than in soldiers and alates. Conclusion These results suggest that SgAbd and Abd are the key components of the endocuticle. We infer that the thicker endocuticle in workers is helpful for them to perform their functions against environmental stress.