Disease relevance of Yp2

• Drosophila yolk protein produced in E. coli is accumulated by mosquito ovaries [1].
• The results presented in this report show that the female sterility, whenever it exists, is due to prevention of vitellogenin synthesis in the fat body, but other abnormalities such as defects with the hybrid ovaries are not excluded [2].
• Heat stress in wild-type females results in oocyte maturation delays, degradation of early vitellogenic egg chambers, inhibition of yolk protein gene expression in follicle cells and accumulation of mature oocytes [3].
• We have estimated that during the steady state of vitellogenin synthesis, a fly can synthesize in 24 h at least 152 micrograms of vitellogenins, which is more than 2% of its body weight, at an average rate of about 6.3 micrograms vitellogenins/h. About 2 micrograms of this are synthesized in the fat body, and about 4 micrograms in the ovaries [4].
• We have expressed two antifreeze protein genes from the Atlantic wolffish, Anarhichas lupus, in Drosophila melanogaster by placing them under the divergent transcriptional control of the host yolk polypeptide (1 and 2) gene promoters [5].

High impact information on Yp2

• Two LDLRs in flies, Arrow, which is required for Wingless signal transduction, and Yolkless, which is required for yolk protein uptake during oogenesis, both require boca function [6].
• Sex-specific regulation of yolk protein gene expression in Drosophila [7].
• The results of temperature shift experiments with abdomens isolated from tra-2ts homozygotes support the notion that the tra-2+ function acts in a cell-autonomous manner to control YP synthesis [7].
• These experiments raise the question of the functional role of the proximity of Yp1 and Yp2 and provide a mechanism for a search for mutations altering the hormonally regulated function of these three genes [8].
• We have isolated recombinant DNA clones that contain the genomic sequences coding for the three most abundant proteins in Drosophila eggs, the yolk proteins (YP1, YP2 and YP3) [9].

Biological context of Yp2

• Embryos were transformed with a hybrid gene consisting of the promotor and amino terminal 430 codons of the Yp2 gene fused to the cytoplasmic form of the invertase gene from the yeast Saccharomyces cerevisiae [10].
• The Vg1 genes have two introns at the same positions as those in D. melanogaster Yp3; the Vg2 genes have only one of the introns, as do D. melanogaster Yp1 and Yp2 [11].
• An examination of these isolated genes and of their DNA complements in the Drosophila genome showed that each of the three coordinately expressed yolk proteins is encoded by a different single-copy gene [9].
• Earlier molecular studies demonstrated that (a) normally yolk protein is synthesized in the fat body, secreted into the hemolymph and taken up by the ovary, (b) the 1163 mutation causes a single amino acid substitution in YP1, and (c) females homozygous for the mutation, or heterozygous females raised at 29 degrees C, retain YP1 in the fat body [12].
• In many insects, development of the oocyte arrests temporarily just before vitellogenesis, the period when vitellogenins (yolk proteins) accumulate in the oocyte [13].

Anatomical context of Yp2

• The amount of each YP synthesized and secreted into the hemolymph is related to the dosage of the above regions, suggesting that the structural genes are in those intervals [8].
• Genetically modified yolk proteins precipitate in the adult Drosophila fat body [12].
• Consistent with its role in yolk uptake, immunogold labeling of the receptor reveals Yl in endocytic structures at the cortex of wild-type vitellogenic oocytes [13].
• The yolk proteins are synthesized in the fat body of adult females, and in the ovarian follicle cells surrounding the developing oocyte during stages 8-10 of oogenesis [14].
• Alternatively, females homozygous or hemizygous for weak alleles produce yolk-filled oocytes, but the number of coated pits and coated vesicles within these oocytes is 50% of that found in the oocytes of wild-type females [15].

Associations of Yp2 with chemical compounds

• Tyrosine sulfation of yolk proteins 1, 2, and 3 in Drosophila melanogaster [16].
• Radioimmunolabeling after two-dimensional polyacrylamide gel electrophoresis was used to identify these proteins as yolk proteins 1, 2, and 3 [16].
• NH2-terminal sequencing showed that this tyrosine residue corresponded to tyrosine 172 of the yolk protein 2 precursor (Hung, M.-C., and Wensink, P. C. (1983) J. Mol. Biol. 164, 487-492) in the sequence Glu-Thr-Thr-Asp-Tyr(S)-Ser-Asn-Glu-Glu [17].
• The Golgi apparatus and the yolk spheres of wild-type ovarian follicles were preferentially labelled by fixation with osmium zinc iodide (OZI) [18].
• Homology of Drosophila yolk proteins and the triacylglycerol lipase family [19].

Other interactions of Yp2

• Two regions of the genome, a 1-kbp portion of the zeste locus and a 1.1-kbp portion of the yolk protein 2 locus, were sequenced in six individuals from each of four species: Drosophila melanogaster, D. simulans, D. mauritiana, and D. sechellia [20].

Analytical, diagnostic and therapeutic context of Yp2

• To initiate a genetic study of the hormonal regulation of genes coding for the three vitellogenins or yolk polypeptide precursors (YPs) in Drosophila, we have isolated from wild flies genetic variants which alter the mobility in SDS-PAGE of each YP independently [8].
• Immunocytochemistry demonstrated that the hybrid protein became localized in yolk granules as oocytes developed [10].
• The present results, together with the recently reported molecular cloning of the yolk protein genes, make the yolk proteins suitable objects for genetic approaches to investigate the biological role(s) of tyrosine sulfation of secretory proteins [16].
• After digestion of yolk protein 2 with trypsin and reversed-phase high performance liquid chromatography, the sulfate label was recovered in two distinct sulfopeptides which, however, had identical NH2-terminal sequences and contained 3 tyrosine residues each [17].
• Transcripts of the yolk protein genes (yp) were quantified by Northern blotting [21].

References