Mutation of a Cuticular Protein,BmorCPR2, Alters Larval Body Shape and Adaptability in Silkworm,Bombyx mori

Abstract

Cuticular proteins (CPs) are crucial components of the insect cuticle. Although numerous genes encoding cuticular proteins have been identified in known insect genomes to date, their functions in maintaining insect body shape and adaptability remain largely unknown. In the current study, positional cloning led to the identification of a gene encoding an RR1-type cuticular protein, BmorCPR2, highly expressed in larval chitin-rich tissues and at the mulberry leaf-eating stages, which is responsible for the silkworm stony mutant. In the Dazao-stony strain, the BmorCPR2 allele is a deletion mutation with significantly lower expression, compared to the wild-type Dazao strain. Dysfunctional BmorCPR2 in the stony mutant lost chitin binding ability, leading to reduced chitin content in larval cuticle, limitation of cuticle extension, abatement of cuticle tensile properties, and aberrant ratio between internodes and intersegmental folds. These variations induce a significant decrease in cuticle capacity to hold the growing internal organs in the larval development process, resulting in whole-body stiffness, tightness, and hardness, bulging intersegmental folds, and serious defects in larval adaptability. To our knowledge, this is the first study to report the corresponding phenotype of stony in insects caused by mutation of RR1-type cuticular protein. Our findings collectively shed light on the specific role of cuticular proteins in maintaining normal larval body shape and will aid in the development of pest control strategies for the management of Lepidoptera.T HE cuticle covering the entire body surface of insects not only participates in defense against pathogens and adverse environmental factors, but is also indispensable for constructing and maintaining external morphological characteristics and locomotion during the entire developmental process (Wigglesworth 1957;Delon and Payre 2004;Moussian et al. 2005). Therefore, the cuticle greatly enhances survival ability and adaptability of insects, ensuring its continued existence as one of the most successful life forms in the animal kingdom.The cuticle is a complex composite material mainly comprising chitin fibers and proteins (Andersen et al. 1995;Moussian 2010). Chitin is the polymer of b-1,4-linked N-acetyl-D-glucosamine (Gilbert 2011, Chap. 7). In procuticles, chitin fibers are arranged in laminae in an antiparallel manner and superimpose each other, forming sheets of fibrils that are stacked in a helicoidal fashion, maintaining cuticle structure, elasticity, and stability (Bouligand 1965;Neville and Luke 1969;Moussian 2010). In terrestrial insects, the chitin content is positively correlated with body size, suggesting a close relationship with cuticle extension and expansion (Merzendorfer and Zimoch 2003;Lease and Wolf 2010).Cuticular proteins (CPs), the principal structural constituents of cuticle, are encoded by more than 100 genes in known insect genomes (Andersen et al. 1995 The soft, flexible cuticle of Lepidoptera larvae not only bears pressure from ...

Annotation and expression analysis of cuticular proteins from the tobacco hornworm, Manduca sexta

“…In a similar fashion, the corresponding genes in B. mori ( BmCPR2-5 ) were among the top expressing genes during the pre- and post-molt 5 th instar larval stage (Okamoto et al, 2008). Recently, Qiao and coworkers (2014) identified BmCPR2 as the gene responsible for the stony mutant in B. mori . This mutation lead to significant defects in cuticle extension, tensile strength, larval mobility, and body shape.…”

Comparative transcriptomic analysis of larval and adult Malpighian tubules from the cotton bollworm Helicoverpa armigera

“…Notably, we found that 37 development‐related unigenes were differentially expressed in larvae compared to adults, for example, storage proteins (lipoprotein and arylphorin), molting regulated proteins (CYP314A1 and ecdysone oxidase), and cuticular protein (Iga & Kataoka, ; Dong et al ., ; Luan et al ., ; Qiao et al ., ; Burmester, ; Li et al ., ). On the other hand, four reproduction‐related unigenes were much more expressed in adults than larvae, among which G1150 encoding vitellogenin had the highest Log 2 FC value of 9.1, as well as the greatest RPKM value (2948) in adult MTs.…”

Melanism patches up the defective cuticular morphological traits through promoting the up-regulation of cuticular protein-coding genes in Bombyx mori

“…Firstly, individuals of the F 2 or BC 1 generations were separated by their cuticle pigmentation. Subsequently, their phenotypes were further classified by morphological characteristics, touch feeling, and the ratios between the number of internodes and intersegmental folds in the second, third, and fourth abdominal segments based on an earlier method (Qiao et al . 2014).…”

“…Total RNA extraction, reverse transcription and Quantitative reverse transcription-PCR (qRT-PCR) conducted as described previously (Qiao et al . 2014).…”

“…2014). And the stony mutant ( st , 8-0.0) which precisely caused by the deletion of a RR1-type larval cuticular protein-encoding gene, BmLcp17 (or BmorCPR2 ) showed hard and tight touch feeling, uncoordinated ratios of the length of the internodes and the intersegment folds (I/IF), bulges at intersegment folds, and severely defective locomotion and behavioral activities in the larval stage (Qiao et al . 2014).…”