Submitted to: Journal of Molecular Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 17, 2002
Publication Date: N/A
Interpretive Summary: In most insects and other egg-laying animals, developing eggs gather and store a protein in the yolk called "vitellogenin" (Vg). However, some flies use an unrelated kind of protein called "yolk protein" (YP) instead of Vg. Moths have both Vg and a less abundant protein called YP2 or "egg-specific protein" (ESP). Both the fly and the moth proteins are related to a class of proteins called lipases, which are found in many organisms, and which help break down fats. In this paper, an analysis of the amino acid (protein building blocks) sequences shows that the YP's of flies and the YP2/ESP's of moths are evolutionarily related to each other.
Technical Abstract: In most oviparous animals, including insects, vitellogenin (Vg) is the major yolk protein precursor. However, in the higher Diptera (cyclorrhaphan flies), a class of proteins homologous to lipoprotein lipases called yolk proteins (YP) are accumulated by oocytes instead of Vg, which is not produced at all. It has been a mystery why the higher Diptera aapparently abandoned Vg, the major yolk protein precursor in lower dipterans such as mosquitoes, and concurrently recruited a lipoprotein lipase to serve as yolk protein precursor. Lepidopterans (moths) produce Vg as the major yolk protein precursor, but also manufacture a class of minor yolk proteins referred to as egg-specific proteins (ESP) or YP2's. Although the lepidopteran ESP/YP2's are related to lipoprotein lipases, previous attempts to demonstrate their homology with higher-dipteran YP's were unsuccessful. In this paper, a multiple alignment of amino acid sequences was constructed using a shared lipid binding motif as an anchor to demonstrate that lepidopteran ESP/YP2's, higher-dipteran YP's, and lipoprotein lipases are indeed homologous. Phylogenetic analyses were performed using both distance-based and parsimony strategies. It is apparent that the higher dipterans have not requisitioned a lipoprotein lipase to replace Vg as a yolk protein precursor, but instead utilize a class of proteins with an evolutionary history of use as minor constituents of yolk in other insects.