Abstract
Imaginal disc growth factors (IDGFs) are a small protein family found in insects. They are related to chitinases and implicated in multiple functions, including cell growth stimulation, antimicrobial activity, insect hemolymph clotting, and maintenance of the extracellular matrix. A number of new IDGFs have been found in several insect species and their detailed phylogenetic analysis provides a good basis for further functional studies. To achieve this goal, we sequenced Idgf cDNAs from several lepidopteran and trichopteran species and supplemented our data with sequences retrieved from public databases. A comparison of Idgf genes in different species showed that Diptera typically contain several Idgf paralogs with a simple exon-intron structure (2–3 exons), whereas lepidopteran Idgfs appear as a single copy per genome and contain a higher number of exons (around 9). Our results show that, while lepidopteran Idgfs, having single orthologs, are characterized by low divergence and stronger purifying selection over most of the molecule, the duplicated Idgf genes in Diptera, Idgf1 and Idgf4, exhibit signs of positive selection. This characterization of IDGF evolution provides, to our knowledge, the first information on the changes that formed these important molecules.
Highlights
Imaginal disc growth factors (IDGFs) are a small glycoprotein family of chitinase-related secretory proteins found in a number of insect species
We found that more than 80% of the IDGF molecule is under negative selection within Lepidoptera, with selected sites mostly localized in conserved domains needed for stability of the8 -barrel structure
IDGFs are insect-specific proteins that evolved from a common ancestor that preceded the separation of Polyneoptera, Condylognatha, and Holometabola
Summary
Imaginal disc growth factors (IDGFs) are a small glycoprotein family of chitinase-related secretory proteins found in a number of insect species. They were originally discovered as mitogenic factors produced by Drosophila melanogaster imaginal disc and embryonic cell lines [1,2]. IDGFs differ from canonical chitinase enzymes by an extra loop sequence (24 extra amino acid residues) between β-sheet 4 and α-helix 4 They contain an amino acid substitution of a key glutamic acid residue in the hydrolase active centre; IDGFs do not possess enzymatic chitinase activity [8]. The three-dimensional structure of one IDGF family member, IDGF2, has been determined at Insects 2019, 10, 365; doi:10.3390/insects10100365 www.mdpi.com/journal/insects
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