The roles of mucus‐forming mucins, peritrophins and peritrophins with mucin domains in the insect midgut

Abstract

Most insects have a gut lined with a peritrophic membrane (PM) consisting of chitin and proteins, mainly peritrophins that have chitin-binding domains. The PM is proposed to originate from mucus-forming mucins (Mf-mucins), which acquired a chitin-binding domain that interlocked with chitin, replacing mucus in function. We evaluated the expression of Mf-mucins and peritrophins by RNAsequencing (RNA-seq) throughout the midgut of four distantly related insects. Mf-mucins were identified as proteins with high o-glycosylation and a series of uninterrupted Pro/Thr/Ser residues. The results demonstrate that the mucus layer is widespread in insects, and suggest that insect Mfmucins are derived from those found in other animals by the loss of the cysteine knot and von Willebrand domains. The data also support a role of Mfmucins in protecting the middle midgut of Musca domestica against acidic buffers. Mf-mucins may also produce a jelly-like material associated with the PM that immobilizes digestive enzymes in Spodoptera frugiperda. Peritrophins with a domain similar to Mf-mucins may be close to the ancestor of peritrophins. Expression data of peritrophins and chitin synthase genes throughout the midgut of M. domestica, S. frugiperda and Tenebrio molitor indicated that peritrophins were incorporated along the PM, according to their preferential sites of formation. Finally, the data support the view that mucus has functions distinct from the PM.

Identification and characterization of two novel peritrophic membrane (PM) genes in the Chinese mitten crab Eriocheir sinensis that exhibit activity against high-pH stress and Aeromonas hydrophila challenge

“…Previous studies have shown that the origin and function of the PM in the Chinese mitten crab may be very different from that in insects (Huang et al, ; Li, Cai, et al, ). For example, the PM lines the midgut epithelium in insects (Dias et al, ). However, in the Chinese mitten crab, the PM has been observed in the stomach and hindgut but was not obvious in the midgut under a microscope (Li, Cai, et al, ).…”

“…The PM is composed of proteins (peritrophins) that are interlocked with chitin fibrils that are associated with other proteins (Dias et al, 2018;Tellam, Wijffels, & Willadsen, 1999). Peritrophins account for approximately 35%-55% of the total mass of the PM in many insects, and the sizes or molecular weights of these proteins vary greatly (Elvin et al, 1996;Hu et al, 2012;Wang & Granados, 2010).…”

The Evolution, Gene Expression Profile, and Secretion of Digestive Peptidases in Lepidoptera Species

“…For trypsins, the largest numbers of gene copies are observed in the genomes of species from the Noctuidae (28 to 42), Plutellidae (37), and Sphingidae (35) moth families (Tables S1,S2). The number of genes encoding chymotrypsins is highest in the genomes of species from the moth families Plutellidae (71) and Noctuidae (32 to 58) and the butterfly family Pieridae (61) ( Tables S3,S4).…”

Insights into the evolution of digestive systems from studies of Trichoplax adhaerens

“…Reproduced from (Smith et al 2015) of food into the digestive cavity/tract and to expel undigestible material and feces. Mucous also protects the digestive epithelium from harmful molecules, such as digestive enzymes, and microorganisms (Bakshani et al 2018;Dias et al 2018;Liévin-Le Moal and Servin 2006). Mucocytes have not been reported in adult Porifera, but mucous-secreting cells are present in larval sponges (Homoscleromorpha-Ereskovsky et al 2007; Demospongiae- Leys and Degnan 2001).…”