- In the crustacean Cherax quadricarinatus , alterations of multi-transcript expression patterns between intermolt and late premolt stages were identified in the hypodermis and in the gastrolith disk via a cDNA microarray. The gastrolith disk is a specialized epithelium forming the gastroliths at premolt. The gastroliths are deposits of calcium carbonate derived from the digested cuticle contributing the mineral to the newly formed exoskeleton at postmolt. The late premolt stage was characterized by a dramatic general up-regulation of genes in the gastrolith disk. This phenomenon is explained by the gastrolith disk function rapid formation of the relatively large gastrolith during a short period of time. Besides genes of general importance for this dramatic change, three genes related to the chitin–protein–mineral structure were identified. The cDNA and the deduced protein of the novel one of them, the chitin deacetylase 1 (Cq-CDA1) was fully characterized and its resemblance to already characterized structural proteins of the gastrolith matrix was described. Cq-CDA1 characteristics strongly indicate its participation in the gastrolith construction, although its protein product was not identified yet in the gastrolith. In addition, many differentially expressed genes with unknown function were elucidated. An unexpected milder down-regulation was observed in the hypodermis.