Submitted to: Insect Biochemistry and Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/20/2008
Publication Date: 9/1/2008
Citation: Arakane, Y., Specht, C.A., Kramer, K.J., Muthukrishnan, S., Beeman, R.W. 2008. Chitin synthases are required for survival, fecundity and egg-hatch in the red flour beetle, Tribolium castaneum. Insect Biochemistry and Molecular Biology. 38(10): 959-962. Doi: http://dx.doi.org/10.1016/j.ibmb.2008.07.006.
Interpretive Summary: Chitin is the main component of the cuticle which forms a protective outer covering of insects and is also required for the lining of the digestive sac. We have recently characterized the roles of the two chitin synthase enzymes in exoskeleton and midgut of larvae, but there is very little evidence concerning the functions of these two enzymes in embryos or adults. We used a technique called “RNA interference” to selectively eliminate the function of each of the two genes in the red flour beetle to see if either enzyme is required at these stages of development. We showed that both enzymes are required for adult reproductive success. Without the first enzyme, adults either do not lay eggs at all, or if they do, the eggs are defective and do not hatch. Without the second enzyme, the adults can’t digest food, and die of starvation. Studies such as these will lead to better understanding of insect growth and development and better strategies for disrupting the associated genes for pest control.
Technical Abstract: The synthesis of chitin, the Beta-1,4-linked polymer of N-acetylglucosamine, is catalyzed by chitin synthase (CHS). Chitin is essential for the structural integrity of the exoskeletal cuticle and midgut peritrophic membrane (PM) of insects. To study the functions of the two chitin synthase genes, TcCHS-A and TcCHS-B, during embryonic and adult development in the red flour beetle, Tribolium castaneum, RNA interference (RNAi) experiments were carried out. When dsRNA for TcCHS-A was injected into male or female pharate adults, all insects died 5-7 d after the adult molt, and the females failed to oviposit prior to death. When dsTcCHS-A was injected into young adults 1-2 d post-eclosion, a similar lethal phenotype was obtained after 5 days and no oviposition occurred. When dsTcCHS-A injections were delayed until after adult maturation (7-10 d post-eclosion) the treated females did oviposit and the resulting embryos appeared to develop normally, but the chitin content of the embryos was dramatically reduced, the embryos became twisted and enlarged, and the eggs did not hatch. Adults treated with dsRNA for TcCHS-B exhibited little or no chitin in their PM and died about 2 weeks after injection. None of the TcCHS-B–treated females oviposited. These results extend our previous findings that CHS genes are required for all types of molts. The present study also demonstrates that these genes have additional roles in embryonic and adult development as well as in fecundity.