Abstract: 【Aim】 To investigate the molecular characteristics of the endocuticle structural glycoprotein gene (TmAbd4) and its role in endocuticle formation in Tenebrio molitor, and so as to provide a theoretical basis for screening the key target genes involved in the growth and development of T. molitor. 【Methods】 The full-length cDNA sequence of TmAbd4 was obtained based on the transcriptome database of T. molitor, and the functional domains of TmAbd4 were analyzed using bioinformatics tools. RT-qPCR was employed to detect the expression levels of TmAbd4 in different tissues (integument, fat body, Malpighian tubules, foregut, midgut and hindgut) of the 13th instar mature larvae and in the integument of the 1-15-day-old mature larvae of T. molitor. After the silence of TmAbd4 in the 13th instar mature larvae of T. molitor by RNAi, the microstructure of the integument was observed using hematoxylin and eosin staining (H&E), and the ultrastructure of the integument was observed through transmission electron microscopy (TEM). 【Results】 The full-length cDNA sequence of TmAbd4 of T. molitor was 506 bp, with an open reading frame (ORF) of 396 bp, encoding 131 amino acids. TmAbd4 contained a signal peptide, a chitin-binding domain 4 (ChtBD4), and a conserved RR-1 motif, classifying it within the RR-1 subclass of the CPR family. TmAbd4 was specifically highly expressed in the integument, and was significantly highly expressed in the integument of the first 3 d after the molting of the 13th instar mature larvae. Injection of dsTmAbd4 caused no visible abnormal phenotypes in T. molitor from molt to pupal stage, however, the endocuticle was observed significantly thinner compared to the dsGFP-injected control group. 【Conclusion】TmAbd4 belongs to the RR-1 subclass of the CPR family and is highly expressed in the integument of T. molitor, with significantly higher expression during endocuticle formation. Silencing of TmAbd4 did not impair the ability of the larvae to molt into the pupal stage, however, it led to a significant reduction in endocuticle thickness, indicating that TmAbd4 involves the formation of endocuticle.

Key words: Tenebrio molitor, cuticle, endocuticle structural protein, molecular characteristics, biological function, microstructure, ultrastructure