title: Not only for egg yolk--functional and evolutionary insights from expression, selection, and structural analyses of Formica ant vitellogenins.
abstract: Vitellogenin (Vg), a storage protein, has been extensively studied for its egg-yolk precursor role, and it has been suggested to be fundamentally involved in caste differences in social insects. More than one Vg copy has been reported in several oviparous species, including ants. However, the number and function of different Vgs, their phylogenetic relatedness, and their role in reproductive queens and nonreproductive workers have been studied in few species only. We studied caste-biased expression of Vgs in seven Formica ant species. Only one copy of conventional Vg was identified in Formica species, and three Vg homologs, derived from ancient duplications, which represent yet undiscovered Vg-like genes. We show that each of these Vg-like genes is present in all studied Hymenoptera and some of them in other insects as well. We show that after each major duplication event, at least one of the Vg-like genes has experienced a period of positive selection. This, combined with the observation that the Vg-like genes have acquired or lost specific protein domains suggests sub- or neofunctionalization between Vg and the duplicated genes. In contrast to earlier studies, Vg was not consistently queen biased in its expression, and the caste bias of the three Vg-like genes was highly variable among species. Furthermore, a truncated and Hymenoptera-specific Vg-like gene, Vg-like-C, was consistently worker biased. Multispecies comparisons are essential for Vg expression studies, and for gene expression studies in general, as we show that expression and also, putative functions cannot be generalized even among closely related species.
authors.affiliation: Department of Biosciences, Centre of Excellence in Biological Interactions, University of Helsinki, Helsinki, FinlandTvärminne Zoological Station, University of Helsinki, Helsinki, Finland claire.morandin@helsinki.fi.
authors.forename: Claire
authors.initials: C
authors.lastname: Morandin
authors.affiliation: Department of Biosciences, Centre of Excellence in Biological Interactions, University of Helsinki, Helsinki, FinlandDepartment of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, Aas, Norway.
authors.forename: Heli
authors.initials: H
authors.lastname: Havukainen
authors.affiliation: Department of Biosciences, Centre of Excellence in Biological Interactions, University of Helsinki, Helsinki, FinlandDepartment of Biology and Biocenter Oulu, University of Oulu, Oulu, Finland.
authors.forename: Jonna
authors.initials: J
authors.lastname: Kulmuni
authors.affiliation: Department of Biosciences, Centre of Excellence in Biological Interactions, University of Helsinki, Helsinki, Finland.
authors.forename: Kishor
authors.initials: K
authors.lastname: Dhaygude
authors.affiliation: Department of Biosciences, Centre of Excellence in Biological Interactions, University of Helsinki, Helsinki, FinlandDepartment of Biological and Environmental Science, University of Jyväskylä, Jyväskylä, Finland.
authors.forename: Kalevi
authors.initials: K
authors.lastname: Trontti
authors.affiliation: Department of Biosciences, Centre of Excellence in Biological Interactions, University of Helsinki, Helsinki, FinlandTvärminne Zoological Station, University of Helsinki, Helsinki, Finland.
authors.forename: Heikki
authors.initials: H
authors.lastname: Helanterä
mesh_terms: D000818:Animals; D001000:Ants / Q000145:classification* / Q000378:metabolism*; D019143:Evolution, Molecular; D005260:Female; D020440:Gene Duplication; D019476:Insect Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D008297:Male; D008958:Models, Molecular; D010802:Phylogeny; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D012641:Selection, Genetic; D017385:Sequence Homology; D014819:Vitellogenins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism
chemical_list: D019476:Insect Proteins; D014819:Vitellogenins
keywords: Formica; caste; gene duplication; gene expression; protein modeling; social insects; vitellogenin