A novel alternative splicing site of class A chitin synthase from the insect Ostrinia furnacalis – Gene organization, expression pattern and physiological significance

Insect chitin synthase A (CHSA) catalyzes chitin biosynthesis in tissues that develop from ectoderm. Since only one gene copy encodes CHSA, we hypothesized that CHSA is very likely to exist as isoforms through alternative splicing, and the functions of these isoforms may be tissue-specific. Besides the known alternative splicing exons in the mid-ORF region, we report here the alternative exons (OfCHSA-2a and OfCHSA-2b) of OfCHSA, the chitin synthase A from the lepidopteran pest Ostrinia furnacalis. Sequence analysis of the 5′ upstream region of the transcription start site indicated that presences of two independent promoters for controlling the expression of OfCHSA-2a/b. Both OfCHSA-2a and OfCHSA-2b transcripts were preferentially expressed in the epidermis. During growth and development of O. furnacalis, OfCHSA-2a was mainly expressed during larval–larval molting and larval–pupal transformation, as well as in newly-laid eggs, while OfCHSA-2b was expressed only during the larval–larval molting. Gene silencing of OfCHSA-2a caused incomplete molting, while silencing of OfCHSA-2b exclusively influenced the head cuticle formation of the 3rd instar larval. Since O. furnacalis is phylogenetically close to the model insect Bombyx mori, the same undiscovered alternative splicing exon was also identified in BmCHSA by gDNA sequence alignment. This work may lead to greater understanding of the mechanism by which a single copy of the CHSA gene could fulfill various functions with tissue specificity.

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► Insect chitin synthase A contains undiscovered alternative splicing first exons.
► The two alternative exons possess distinctive promoters and regulating elements.
► One specifically functions during molting and metamorphosis.
► The other specifically functions during larval–larval molting.
► Bombyx mori also contains the same alternative exons.