Chitin is one of the most important biopolymers in nature. It is mainly produced by fungi, arthropods and nematodes. In insects, it functions as scaffold material, supporting the cuticles of the epidermis and trachea as well as the peritrophic matrices lining the gut epithelium. Insect growth and morphogenesis are strictly dependent on the capability to remodel chitin-containing structures. For this purpose, insects repeatedly produce chitin synthases and chitinolytic enzymes in different tissues. Coordination of chitin synthesis and its degradation requires strict control of the participating enzymes during development. In this review, we will summarize recent advances in understanding chitin synthesis and its degradation in insects.

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Chitin metabolism in insects: structure, function and regulation of chitin synthases and chitinases

Biology of the Arthropod Cuticle

Publisher Summary In their carbohydrate metabolism, insects make use of substances, enzymes and operational principles that are known from other living groups. Occupying a central place among the knowledge of carbohydrate metabolism in insects is the presence of trehalose as the predominant blood sugar. Its distribution and the relations of its metabolism to the mechanisms of nutrient absorption, storage and supply to the tissues, are discussed. Characteristic of insects and other arthropods is the presence of chitin as a structural component of the exoskeleton, which in its deposition and resorption interacts closely with the metabolism of other carbohydrates. The mucopolysaccharides of insect hemolymph and tissues have only recently begun to be investigated. This chapter focuses on a metabolic process, which apparently peculiar to insects and some other arthropods is the bulk conversion of glycogen to glycerol and sorbitol. Insects have provided the material for several well-known original biochemical discoveries. The chapter also presents an investigation of the biochemistry of this animal group, which has in general lagged far behind that of micro-organisms on the one hand and vertebrate animals on the other.

The Biochemistry of Sugars and Polysaccharides in Insects

Biochemistry of Insect Cuticle

Choosing the right nutrients to consume is essential to health and wellbeing across species. However, the factors that influence these decisions are poorly understood. This is particularly true for dietary proteins, which are important determinants of lifespan and reproduction. We show that in Drosophila melanogaster, essential amino acids (eAAs) and the concerted action of the commensal bacteria Acetobacter pomorum and Lactobacilli are critical modulators of food choice. Using a chemically defined diet, we show that the absence of any single eAA from the diet is sufficient to elicit specific appetites for amino acid (AA)-rich food. Furthermore, commensal bacteria buffer the animal from the lack of dietary eAAs: both increased yeast appetite and decreased reproduction induced by eAA deprivation are rescued by the presence of commensals. Surprisingly, these effects do not seem to be due to changes in AA titers, suggesting that gut bacteria act through a different mechanism to change behavior and reproduction. Thus, eAAs and commensal bacteria are potent modulators of feeding decisions and reproductive output. This demonstrates how the interaction of specific nutrients with the microbiome can shape behavioral decisions and life history traits.

/pdf/commensal-bacteria-and-essential-amino-acids-control-food-1d093xsexf.pdf

Commensal bacteria and essential amino acids control food choice behavior and reproduction.

1. In vivo studies on 5th instar and adult locusts revealed that chitin formation in thorax, abdomen, hind leg and wing was greatest during the first few days after moulting.

2. Wing extracts were used for in vitro experiments, and evidence was obtained for the presence of the following enzymes: hexokinase, phosphohexose isomerase, glutamine transaminase, phosphoglucosamine transacetylase, acetyl coenzyme-A synthetase, phosphoacetylglucosamine mutase and uridine diphosphate N -acetylglucosamine pyrophosphorylase.

3. The results are discussed, and a tentative scheme is presented for the biosynthesis of chitin in the wing of Schistocerca gregaria .

Studies on Chitin Synthesis in the Desert Locust

Amino acid metabolism in locust tissues.

1. Homogenates of fat-body of Schistocerca gregaria Forsk. were shown to catalyse transamination reactions between α-ketoglutarate and numerous α-amino acids. The aspartate/glutamate and alanine/glutamate transaminases were the most active. They were present in both the ‘soluble’ and the mitochondrial fractions of fat-body cells and also in Malpighian tubules and mid-gut wall. The other transaminases in the fat-body were confined to the mitochondrial fraction. 2. Fat-body, Malpighian tubule and mid-gut wall homogenates were able to convert glutamic acid into glutamine, a compound which could also act as an amino-group donor in some transamination reactions. 3. A glutamate-cytochrome c reductase system which involved diphosphopyridine nucleotide was present in fat-body. 4. Fat-body contained an active arginase, but urease could not be detected. A D-amino-acid oxidase was present, together with a less active L-amino-acid oxidase. 5. In general, it appears that amino-acid metabolism in the locust resembles that in higher animals.

Amino-Acid Metabolism in Locust Tissues

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Studies on Chitin Synthesis in the Desert Locust

Amino acid metabolism in locust tissues.

Amino-Acid Metabolism in Locust Tissues