De novo transcriptome analysis of the excretory tubules of Carausius morosus (Phasmatodea) and possible functions of the midgut ‘appendices’

Abstract

The Malpighian tubules are the insect excretory organs, responsible for ion and water homeostasis and elimination of nitrogenous wastes. Post-genomic assays suggest they also metabolize and detoxify xenobiotic compounds and have antimicrobial properties. The Phasmatodea have an additional, unique set of excretory organs referred to predominantly as midgut appendices. Their function and how it compares to phasmid and other insect Malpighian tubules is unknown. Hypotheses include carbonic anhydrase activity, calcium and metal cation sequestration, and xenobiotic transport. This work presents the first comparative transcriptomic analysis of the Phasmatodean excretory organs, using the model insect Carausius morosus. I produced de novo transcriptomes of the midgut appendices, midgut wall, and Malpighian tubules, and looked for differentially expressed genes associated with putative organ functions. The appendices differentially and highly express lipid transport and metabolism proteins, and the biomineralization gene otopetrin. The Malpighian tubules differentially and highly express acid phosphatases and multiple transporter types, while appendices express fat-soluble vitamin and peptide transporters. Many defense proteins such as multidrug resistance proteins, ABC transporters, cytochrome P450’s, and glutathione-S-transferases were differentially expressed in specific excretory organs. I hypothesize that the appendices and Malpighian tubules both have defensive / xenobiotic metabolism functions, but each likely target different substrates. Phasmid Malpighian tubules excrete as in other insects, while the appendices may predominantly regulate amino acids, fats, and fat-soluble compounds. Lipid metabolism in insects is poorly understood, and the Phasmatodea may thus serve as a model for studying this further.

Blattella germanica displays a large arsenal of antimicrobial peptide genes

“…stephensi are expressed in fat body, midgut, haemolymph and salivary glands with the high level of expression at fat body 49 . On the contrary, a defensin gene from Bemisia tabaci was more highly expressed in adult midgut or salivary glands than in fat bodies 52 and a type of attacin gene was highly expressed in adult Malpighian tubules of the stick insect Carausius morosus 53 . It was also reported constitutive expression of a termicin gene in adult haemolymph and salivary glands from the termite P. spiniger 32 .…”

Gene expression profiles in Malpighian tubules of the vector leafhopper Psammotettix striatus (L.) revealed regional functional diversity and heterogeneity

“…Correlations between the transcriptomes in many tissues or organs of animals (e.g., antennae, salivary glands, midgut, midgut ‘appendices’, hepatopancreas, venom gland, gill) and its respective physiological functions have been reported [ 40 – 45 ]. Similar studies have been carried out for the MTs of a few insect species, but these studies have been limited in viewing the MTs as a whole organ [ 3 , 5 , 10 , 12 , 22 , 25 , 46 – 50 ]. To our knowledge, studies of the transcriptome of vector leafhoppers have mainly focused on the salivary glands and the alimentary tract [ 51 – 55 ].…”

“…Previous studies revealed that the salivary glands and alimentary tract of vector leafhoppers have the ability in the metabolism of natural and synthetic xenobiotics/toxins by expressing a variety of detoxification enzymes [ 51 – 53 ]. Previous studies also suggest that MTs of phytophagous insects display the abundance of enzymes related to detoxification of plant defense compounds, insecticides and other xenobiotic compounds [ 3 , 5 , 8 , 10 , 21 , 22 , 46 , 49 , 50 , 64 ], making the tubules a major site of insecticide detoxification and resistance [ 49 , 65 , 66 ].…”

“…The alimentary tract and salivary glands of vector leafhoppers have been shown to attribute to insect immunological response in the resistance or reduction of microbial infection [ 53 , 54 ]. Research during the past several decades on insect MTs has uncovered that the tubules contribute to activating innate immune defense to withstand the invading pathogens [ 3 – 5 , 8 , 46 , 70 ]. In the present study, we revealed that lysosomal-related acid hydrolases (e.g., proteases, glycosidases and sulfatases) and integral membrane proteins (e.g., lysosomal-associated transmembrane proteins and lysosome-associated membrane glycoprotein) were highly expressed in MT1+2 and MT4 (Additional file 11 : Table S5; Additional file 12 : Figure S7), which are known or speculated to be involved in cellular responses to inflammation and pathogenic infection [ 43 ].…”

Transcriptomic and Neuropeptidomic Analysis of the Stick Insect, Carausius morosus

“…Sequences are listed in Supporting Information S1 and S2, which also consider partial sequences (+). Additionally, obtained sequences with allelic differences, sequences completed from RAW data and publicly available databases33 are indicated by "*". TSA, transcriptome shotgun assembly; SRA, sequence read archive; t , unpublished Trinity assembly; b , unpublished Bridger assembly.…”