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Vitellogenin (Vg) is the precursor of vitellin (Vn) which is the major yolk protein in eggs. In a previous report, we isolated and characterized the first Vg message from the American dog tick Dermacentor variabilis. In the current study, we describe a second Vg gene from the same tick. The Vg2 cDNA is 5956 nucleotides with a 5775 nt open reading frame coding for 1925 amino acids. The conceptual amino acid translation contains a 16-residues putative signal peptide, N-terminal lipid binding domain and C-terminal von Willebrand factor type D domain present in all known Vgs. Moreover, the amino acid sequence shows a typical GLCG domain and several RXXR cleavage sites present in most isolated Vgs. Tryptic digest-mass fingerprinting of Vg and Vn recognized 11 fragments that exist in the amino acid translation of DvVg2 cDNA. Injection of virgin females with 20 hydroxyecdysone induced DvVg2 expression, vitellogenesis and oviposition. Using RT-PCR, DvVg2 expression was detected only in tick females after mating and feeding to repletion. Northern blot analysis showed that DvVg2 is expressed in fat body and gut cells of vitellogenic females but not in the ovary. DvVg2 expression was not detected in adult fed or unfed males. The characteristics that distinguish Vg from other similar tick storage proteins like the carrier protein, CP (another hemelipoglycoprotein) are discussed., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Abstract: Many species of mites and ticks are of agricultural and medical importance. Much can be learned from the study of transcriptomes of acarines which can generate DNA-sequence information of potential target genes for the control of acarine pests. High throughput transcriptome sequencing can also yield sequences of genes critical during physiological processes poorly understood in acarines, i.e., the regulation of female reproduction in mites. The predatory mite, Phytoseiulus persimilis, was selected to conduct a transcriptome analysis using 454 pyrosequencing. The objective of this project was to obtain DNA-sequence information of expressed genes from P. persimilis with special interest in sequences corresponding to vitellogenin (Vg) and the vitellogenin receptor (VgR). These genes are critical to the understanding of vitellogenesis, and they will facilitate the study of the regulation of mite female reproduction. A total of 12,556 contiguous sequences (contigs) were assembled with an average size of 935bp. From these sequences, the putative translated peptides of 11 contigs were similar in amino acid sequences to other arthropod Vgs, while 6 were similar to VgRs. We selected some of these sequences to conduct stage-specific expression studies to further determine their function. [Copyright &y& Elsevier]

Abstract: In mites, vitellogenin synthesis, regulation and uptake by the oocytes as vitellin remain practically unknown. Although a partial sequence of the gene is now available, no previous studies have been conducted that describe the native vitellin protein in mites. The objective of this study was to characterize vitellin in the twospotted spider mite, Tetranychus urticae. The native twospotted spider mite vitellin migrated as a single major band with a molecular weight of 476±14.5kDa as compared to 590±25.5kDa for vitellin from the American dog tick, Dermacentor variabilis. However, isoelectric focusing analysis of native spider mite vitellin showed five bands with pI values slightly acidic to neutral (pH 5.8, 6.2, 6.7, 7.0 and 7.2), as is the case for insect and tick vitellins. Reducing conditions (SDS-PAGE) also revealed multiple subunits ranging from 290.9 to 3.6kDa and was similar to that found in D. variabilis. Spider mite vitellin weakly bound lipids and carbohydrates compared to the tick. Unlike D. variabilis, the spider mite egg yolk protein does not bind heme. The significance of non-heme binding in mites is discussed. [Copyright &y& Elsevier]

Abstract: Lipoglycoproteins in the Chelicerata that bind and store heme appear to represent a unique evolutionary strategy to both mitigate the toxicity of heme and utilize the molecule as a prosthetic group. Knowledge of heme-binding storage proteins in these organisms is in its infancy and much of what is known is from studies with vitellogenins (Vg) and more recently the main hemolymph storage protein in ixodid ticks characterized as a hemelipoglyco-carrier protein (CP). Data have also been reported from another arachnid, the black widow spider, Latrodectus mirabilis, and seem to suggest that the heme-binding capability of these large multimeric proteins is not a phenomenon found only in the Acari. CP appears to be most closely related to Vg in ticks in terms of primary structure but post-translational processing is different. Tick CP and L. mirabilis high-density lipoprotein 1 (HDL1) are similar in that they consist of two subunits of approximate molecular masses of 90 and 100kDa, are found in the hemolymph as the dominant protein, and bind lipids, carbohydrates and cholesterol. CP binds heme which may also be the case for HDL1 since the protein was found to contain a brown pigment when analyzed by native polyacrylamide gel electrophoresis. Vgs in ticks are composed of multiple subunits and are the precursor of the yolk protein, vitellin. The phylogeny of these proteins, regulation of gene expression and putative functions of binding and storing heme throughout reproduction, blood-feeding and development are discussed. Comparisons with non-chelicerate arthropods are made in order to highlight the mechanisms and putative functions of heme-binding storage proteins and their possible critical function in the evolution of hematophagy. [Copyright &y& Elsevier]