Abstract
Chitin, a polymer of N-acetyl-D-glucosamine (GlcNAc), functions as a major structural component in chitin-containing organism including crustaceans, insects and fungi. Recently, we reported that acidic chitinase (Chia) is highly expressed in mouse, chicken and pig stomach tissues and that it can digest chitin in the respective gastrointestinal tracts (GIT). In this study, we focus on major livestock and domestic animals and show that the levels of Chia mRNA in their stomach tissues are governed by the feeding behavior. Chia mRNA levels were significantly lower in the bovine (herbivores) and dog (carnivores) stomach than those in mouse, pig and chicken (omnivores). Consistent with the mRNA levels, Chia protein was very low in bovine stomach. In addition, the chitinolytic activity of E. coli-expressed bovine and dog Chia enzymes were moderately but significantly lower compared with those of the omnivorous Chia enzymes. Recombinant bovine and dog Chia enzymes can degrade chitin substrates under the artificial GIT conditions. Furthermore, genomes of some herbivorous animals such as rabbit and guinea pig do not contain functional Chia genes. These results indicate that feeding behavior affects Chia expression levels as well as chitinolytic activity of the enzyme, and determines chitin digestibility in the particular animals.
Highlights
Chitin-containing organisms, in particular insects, have recently become attractive as a potential novel animal feed resource due to their nutritional values, production cost and a low impact on the environment[31,32,33]
Chia mRNA level is very low in bovine and dog stomach tissues
Bovine Chia mRNA levels were highest in lung and liver (Fig. 1a), which are consistent with a previous report[57]
Summary
Chitin-containing organisms, in particular insects, have recently become attractive as a potential novel animal feed resource due to their nutritional values, production cost and a low impact on the environment[31,32,33]. Mammals, including mice and humans, do not synthesize chitin but possess two active chitinases, chitotriosidase (Chit1) and acidic chitinase (hereafter referred to as “Chia”; alternative name: acidic mammalian chitinase, AMCase) in their genomes[34,35] These mammalian chitinases belong to the family 18 of glycoside hydrolases[35,36,37]. MRNA expression in bovine (a and b) and dog (c) tissues using a standard DNA containing genes fragments including Chia, GAPDH, pepsinogen (Pep) and Chit[1] of bovine and Chia and GAPDH of dog. Both chitinases were quantified by qPCR using the standard DNA. It has been shown that there are single nucleotide polymorphisms in human Chia, which are associated with asthma[47,48,49]
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