Sequence homologies among the three yolk polypeptide (Yp) genes in Drosophila melanogaster

cDNA isolation, expression, and hormonal regulation of yolk protein genes in the oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae)

Yolk protein (YP) or vitellogenin (Vg), the main component of yolk, is the key nutrient for embryonic development. YPs, encoded from uncleaved genes existing mainly in cyclorraphan flies, are different from VGs that are present in most non-cyclorraphan dipterans and other insects. In this study, cDNAs of two YPs, namely Bdyp1 and Bdyp2 (GenBank accession Nos. AF368053 and AF368054), were isolated in the oriental fruit fly, Bactrocera dorsalis (Hendel). RT-PCR analysis revealed that Bdyp1 and 2 are expressed in the fat body and ovary during egg development. However, the expression profiles of Bdyp1 and 2 in the fat body are different, indicating that divergent mechanisms might exist in the regulation of these two genes. Twenty-hydroxyecdysone (20E) plays a major role in promoting Bdyp1 expression, yet the expression of Bdyp2 exhibits a greater response to juvenile hormone (JH) in fat body in vitro. Unexpectedly, 20E-induced expression of both Bdyp1 and 2 is suppressed by JH prior to 20E treatment of in vitro fat body; conversely, it is enhanced by the addition of JH following 20E treatment.

Cyclorraphan yolk proteins and lepidopteran minor yolk proteins originate from two unrelated lipase families

Vitellogenins, cyclorraphan yolk proteins and lepidopteran minor yolk proteins are three classes of female-specific proteins that serve as an embryonic nutritional store. Similarity to vertebrate lipid-binding proteins was established for vitellogenins and yolk proteins, vitellogenins being related to apolipoprotein B and yolk proteins to lipases. Recently, similarity between yolk proteins and minor yolk proteins was reported and it was suggested that yolk proteins are more related to minor yolk proteins than to vertebrate lipases. In this study, we cloned five additional yolk proteins from the grey fleshfly Neobellieria bullata, formerly known as Sarcophaga bullata. We used this sequence data, combined with sequence data retrieved from the NCBI protein database to evaluate the yolk protein-lipase and the yolk protein-minor yolk protein relationship. We found no similarity between yolk proteins and minor yolk proteins, but we showed that yolk proteins are related to a family of lipases containing vertebrate hepatic and pancreatic lipases while minor yolk proteins are related to a family of lipases containing vertebrate gastric and lingual lipases. The fact that three different classes of yolk storage proteins show similarity to three different classes of vertebrate lipid-binding proteins strongly suggests that this lipid-binding feature is important for insect yolk storage proteins.

Molecular markers of endocrine disruption in aquatic organisms

A wide range of organic contaminant compounds prevalent in the aquatic environment has been shown to exhibit hormone-disrupting activity. The actual potency of such compounds are low compared with endogenous hormones, such as 17beta-estradiol, but may still produce detrimental biological effects. Induced hormone levels are routinely measured using commercial testing kits, though these fail to relate to actual effects. Field and laboratory studies on the biological effects of environmental estrogens have, in the past, largely relied on assays of vitellogenin (vtg) induction in male fish, reduced growth in testes formation, and intersex incidence. Here, we critically review the current and potential application of molecular techniques in assessing the adverse biological reproductive effects of endocrine-disrupting chemicals in aquatic organisms. The role of fish (estrogen, androgen, and progestogen) hormone receptors and invertebrate (ecdysone) hormone receptor, egg production (vtg and chorion) proteins, steroid biosynthesis enzymes (aromatase, sulfotransferase, and hydroxysteroid dehydrogenase), DNA damage, apoptosis, and their potential development as biomarkers are discussed in turn. In each case, the sequences characterized are presented and homologies across species are highlighted. Molecular methods of gauging vtg and zona radiata (ZR) expression and protein concentrations have included immunoassay and reverse transcription polymerase chain reaction (RT-PCR). Suggestions for the isolation for key gene expression products (aromatase, ZR, and vtg, for instance), from a wider range of fish species using degenerate primers, are given. Endocrine disruption in invertebrates has received less attention compared with fish, partly because the knowledge regarding invertebrate endocrinology is limited. Here we review and suggest alternate isolation strategies for key players in the imposex induction process: vitellin (Vn), aromatase, and Ala-Pro-Gly-Trp (APGW) amide neurohormone. Current molecular-level techniques rely on ligand-binding assays, enzyme-linked immunosorbent assay (ELISA), and, more recently, gene expression. In the future, more reliance will be placed on the development of gene expression assays using reporter systems combined with cross-species PCR-based or polyclonal antibody-based assays. We discuss the use of recombinant receptors as a means of primary screening of environmental samples for estrogenicity and antiestrogenicity, which avoids species and seasonal variation in receptor response to ligand binding, a recognized problem of earlier bioassays. Most exciting is the potential that microarray and proteomics approaches have to offer. Such techniques are now used routinely in medical research to identify specific genes and proteins affected by treatment with endocrine disruptors, including estradiol. The technique has yet to be used to screen aquatic organisms, but it has the potential to implicate previously unsuspected estradiol-sensitive genes that may later become molecular markers of endocrine disruption.

A hexamerin protein, AgSP-1, is associated with diapause in the boll weevil(1)

The objective of this research was to identify a reliable biochemical indicator for diapause (dormancy) in the boll weevil, Anthonomus grandis. Hemolymph polypeptides from reproductive and diapausing weevils were compared using denaturing sodium dodecyl sulpfate (SDS)-polyacrylamide gel electrophoresis (PAGE). A 77-kDa protein, which proved to be a hexamerin (AgSP-1), strongly correlated with morphological diapause characters in both male and female adult weevils. N-terminal sequence analysis identified the first 25 amino acids of the mature protein and was used to develop an antibody to AgSP-1. Anti-AgSP-1 reacted only with hemolymph from diapausing weevils of both sexes but not with hemolymph from reproductive weevils. Also, the yolk protein, vitellogenin (VG), inversely correlated with AgSP-1. When hemolymph VG was high, AgSP-1 was absent or barely perceptible.Juvenile hormone regulates VG synthesis in most insect species. Juvenile hormone is reported to stimulate reproductive maturation in the boll weevil (Physiological Entomology 22 (1997) 261) and to be absent during diapause (Physiological Entomology 22 (1997a) 269). Therefore, the juvenile hormone (JH) mimic, methoprene, was used to assess the role of JH activity in the boll weevil for terminating diapause, stimulating reproductive maturation and possibly influencing AgSP-1 titers. Application of methoprene was not effective in activating reproductive development. Hemolymph from methoprene-treated, females contained VG and AgSP-1 titers that were similar to acetone-treated and untreated control weevils.Using a genomic DNA library and 3' RACE, two clones were isolated that yielded the complete sequence of AgSP-1 as well as a portion of the 5' untranslated region. Northern blot analysis confirmed the presence of a 2.5 kB transcript for AgSP-1 in the fat body of diapausing weevils. AgSP-1 was also present in the fat body of reproductive weevils, but to a lesser extent. No sex-related differences in gene expression were observed; diapausing weevils of both sexes showed similar levels of AgSP-1 expression. An inverse correlation was observed between the VG transcript and AgSP-1 mRNA. VG was highly expressed in the fat body of reproductive females and only slightly expressed in tissue from diapausing females. Our data suggests that AgSP-1 is a diapause-specific protein in adult weevils and that JH, alone, is not effective in terminating diapause.

Ovarian defects in hybrids of the species pair Drosophila virilis and Drosophila texana

In interspecific matings between Drosophila virilis and Drosophila texana female sterility is observed in F2 hybrid females. A previous study has shown that no vitellogenin synthesis occurs in the fat body of sterile hybrid females. The results presented in this paper show that hybrid ovaries of sterile females transplanted into the abdomens of females of the parental species are not able to develop upon maturity. With few exceptions, the hybrid ovaries remained alive in the host environment, but their oocytes failed to develop to vitellogenic stages. Thus, in hybrid females between Drosophila virilis and Drosophila texana sterility is the result of defects in both the two main developmental processes of egg maturation, the synthesis of vitellogenins in the fat body and the uptake of vitellogenins by the ovary.

Melatonin prevents apoptosis induced by 6-hydroxydopamine in neuronal cells: implications for Parkinson's disease

It was recently reported that low doses of 6-hydroxydopamine (6-OHDA) induce apoptosis of naive (undifferentiated) and neuronal (differentiated) PC12 cells, and this system has been proposed as an adequate experimental model for the study of Parkinson's disease. The mechanism by which this neurotoxin damages cells is via the production of free radicals. Given that the neurohormone melatonin has been reported 1) to be a highly effective endogenous free radical scavenger, 2) to increase the mRNA levels and the activity of several antioxidant enzymes, and 3) to inhibit apoptosis in other tissues, we have studied the ability of melatonin to prevent the programmed cell death induced by 6-OHDA in PC12 cells. We found that melatonin prevents the apoptosis caused by 6-OHDA in naive and neuronal PC12 cells as estimated by 1) cell viability assays, 2) counting of the number of apoptotic cells, and 3) analysis and quantification of DNA fragmentation. Exploration of the mechanisms used by melatonin to reduce programmed cell death revealed that this chemical mediator prevents the 6-OHDA induced reduction of mRNAs for several antioxidant enzymes. The possibility that melatonin utilized additional mechanisms to prevent apoptosis of these cells is also discussed. Since this endogenous agent has no known side effects and readily crosses the blood-brain-barrier, we consider melatonin to have a high clinical potential in the treatment of Parkinson's disease and possibly other neurodegenerative diseases, although more research on the mechanisms is yet to be done.

5' coding region of the follicular epithelium yolk polypeptide 2 cDNA in the moth, Plodia interpunctella, contains an extended coding region

The 5' region of YP2 cDNA, a follicular epithelium yolk protein subunit in the moth, Plodia interpunctella, shows that the polypeptide contains an extended internal coding region. Partial cDNA clones for YP2 were isolated from a pharate adult female ovarian cDNA expression library in Lambda Zap II by screening with antigen selected YP2 antiserum. The 5' sequence of the YP2 transcript was determined by 5' RACE PCR of ovarian mRNA using YP2 sequence-specific nested primers. The combined cDNA and 5' RACE sequencing showed the YP2 transcript to be 1971 bp in length up to the poly(A) tail with a single open reading frame for a predicted polypeptide of 616 amino acids. Northern analysis showed a single YP2 transcript to be present in ovarian RNA that was approximately 2 kb in length. The predicted amino acid sequence for YP2 from P. interpunctella is most closely related to egg specific protein (ESP) from Bombyx mori and the partial YP2 sequence from Galleria mellonella. YP2 from P. interpunctella also is similar to vertebrate lipases and contains a conserved lipid binding region. However, the 5' coding region of YP2 from P. interpunctella contains an in-frame insert of approximately 438 bp that had replaced an approximately 270-bp region as compared with ESP from B. mori and YP2 of G. mellonella. This suggests that the insert occurred by a recombinational event internal to the YP2 structural gene of P. interpunctella.

Structure of the gypsy moth vitellogenin gene

Genomic clones containing the vitellogenin (Vg) gene from the gypsy moth were isolated from two genomic libraries and characterized. The nucleotide sequence of a 16,132 bp region of the gypsy moth genome was determined which included a 3,666 bp region upstream from the transcription initiation site and 499 bp region downstream from the transcribed region. Primer extension analysis was performed to identify the transcription initiation site. Gene sequence confirmed the sequence of VgmRNA recently reported [Hiremath and Lehtoma, J. Insect Biochem. Mol. Biol. (1997) 27:27-35] and indicated that the gypsy moth Vg gene contains seven exons interrupted by six introns. Sequence analysis of the promoter region revealed presence of several motifs associated with sex-specific and developmentally regulated genes in other systems. The nucleotide sequence comparison analyses showed that the gypsy moth Vg gene had considerably similarity with the Bombyx mori Vg gene but not with those from Anthonomous grandis and Aedes aegypti.

Complete nucleotide sequence of the vitellogenin mRNA from the gypsy moth: novel arrangement of the subunit encoding regions

Primary structure analysis and location of introns suggests evolutionary relatedness among vitellogenin (Vg) genes from vertebrates and invertebrates, including insects. We have determined the complete nucleotide sequence of the gypsy moth VgmRNA, which shows that its structure is significantly different from VgmRNAs in other systems. The nucleotide sequence was determined using overlapping cDNA fragments generated from RACE reactions and rTh polymerase-mediated PCR. The VgmRNA is 5579 nucleotides long and codes for both the large and small subunits. However, the arrangement of the subunit encoding regions in the gypsy moth VgmRNA is opposite of what has been observed in other systems. Gypsy moth Vg gene is the first reported example of a Vg gene where the 5'-terminal region codes for the large subunit and the 3'-terminal region for the small subunit. Also, the sequence near the junction of subunits was significantly different from those found in other insects. This may be responsible for the relatively more stable precursor of Vg subunits found in the gypsy moth hemolymph. It is not clear where this divergence in the structure of Vg gene occurred during evolution, since the Vg gene of another lepidopteran, Bombyx mori, conforms to the structure of those in vertebrates and other invertebrates.

Structure of the Bombyx sorbitol dehydrogenase gene: a possible alternative use of the promoter

In an initial effort to understand the molecular mechanism of how low temperature induces sorbitol dehydrogenase gene expression in diapause eggs of the silkworm, the sorbitol dehydrogenase gene was isolated from a Bombyx genomic library using a cDNA encoding the Bombyx homologue of mammalian sorbitol dehydrogenase as a probe. The gene extended for about 10 kb, consisting of eight exons and seven introns. Four TATA motifs were found in the 5' upstream region of the gene, without CCAAT. AATTAA, instead of AATAAA, was localized in the upstream region of the polyadenylation site. Although a single copy of this gene was present per haploid genome, 1.2 kb and 1.1 kb transcripts were found from yolk cells in diapause eggs and from larval fat-body cells, respectively. The two major transcription initiation sites corresponding to both transcripts were localized at 355 and 226 base pairs upstream from the transition start site, indicating an alternative use of promoter. The 5'-upstream region of the gene contained a consensus sequence, TGA(A/T)AA(A/G/T), that has been found in insect genes expressed mainly in larval and pupal fat bodies. It also contained three kinds of sequences similar to cis-elements recognized by members of the steroid receptor superfamily, such as chicken ovalbumin upstream promoter transcription factor (COUP-TF)/Drosophila Seven up (SVP), Drosophila hormone receptor 39 (DHR39) and Bombyx fushi tarazu transcriptional factor 1 (BmFTZ-F1).

Proliferation and motility responses of primary and recurrent gliomas related to changes in epidermal growth factor receptor expression

Astrocytic neoplasms show a high incidence of elevated or mutated epidermal growth factor receptor (EGFR) expression. Although proliferative effects from EGFR activation are well described, the role that changes in this receptor play in glioma growth and migration remain poorly addressed. This report characterizes changes in the levels of EGFR expression in three glial tumors at initial presentation (resection) and at the time of recurrence. By quantitative flow cytometry the mean level of EGFR expression increased, decreased, or remained the same in different recurrent astrocytomas relative to their primary tumor cells. Immunocytochemistry for EGFR on monolayer cells corroborated the level of expression in the recurrent tumors relative to their matched primary specimen. Immunoprecipitation indicated that 170 kd EGFR was expressed in each of the tumors, and showed normal down regulation following treatment with EGF. Proliferation response to EGF was seen in only 1/6 instances, but was concentration-dependent when observed. Stimulated migration of the cells was frequently seen and was also concentration-dependent on EGF; the magnitude of response was related to the relative level of 170 kd EGFR expression in the cells. EGFR immunostaining of tissue sections from the tumors confirmed the levels of EGFR expressed in primary and recurrent astrocytomas as was seen in the cultured cells. These results indicate that the relative levels of EGFR in early passage cell cultures from glioma specimens concurs with the measured tissue levels of expression. Human glioma cells are more responsive to migration induction than proliferation induction by EGF.

The sequence and expression pattern of the Calliphora erythrocephala yolk protein A and B genes

The yolk protein genes (yps) are expressed in a temporal, tissue- and sex-specific fashion in Drosophila melanogaster. Here we report the sequence of two related genes in Calliphora erythrocephala. The predicted Calliphora yolk protein (YP) sequences are well conserved, especially at the C-terminal end when compared to those of D. melanogaster and Ceratitis capitata. Database searches with the Calliphora yolk protein B (CeYPB) sequence identify the vertebrate lipase similarity reported for the YPs of Drosophila and Ceratitis. Moreover, sequences with identity to divalent ion-binding sites were observed, which colocalized with putative tyrosine sulfation sites. Calliphora oogenesis differs from Drosophila in that it is cyclic in response to a meat feed. The Calliphora yp genes are expressed in the follicle cells of the egg chamber during vitellogenesis, as shown by in situ hybridization, and the yp message levels correlate with YP synthesis. The synthesis of the yp transcripts in ovaries of Calliphora occurs in the same pattern as that for ovarian transcripts in Drosophila. In the carcass, yp transcript levels are correlated with the production of a batch of eggs.

Comparative analysis of the sequence and structure of two Drosophila melanogaster genes encoding vitelline membrane proteins

Two Drosophila melanogaster vitelline membrane protein-encoding genes (VM), located at polytene band positions 26A and 34C, have been cloned and comparatively characterized at the nucleotide level. Sequence analysis of genomic and cDNA clones for the two genes, VM26A.1 and VM34C.1, indicates that both are similarly organized with a central highly conserved domain [Scherer et al., Dev. Biol. 130 (1988) 786-788] which is flanked by unrelated regions, and that both genes lack introns. Comparison of the upstream regions reveals that both VM genes contain a hepatmeric element identical to one associated with the D. melanogaster yolk protein-encoding genes (YP). This heptamer occurs in the specific 5' flanking region responsible for ovarian temporal- and tissue-specific control in both VM and YP genes. A putative chorion transcription factor 2 site is also associated with an upstream control element of VM26A.1, but not with any sequenced portion of VM34C.1.

cDNA cloning and expression of Rhodnius prolixus vitellogenin

It was shown that Rhodnius prolixus vitellogenin (Vg) is synthesized as precursors of 205 and 190 kDa. Each Vg subunit is antigenically related to a domain in the precursor molecules. Since Vg has been previously detected in R. prolixus male adults, protein synthesis by fat bodies from 5th instar male nymphs was investigated and no Vg synthesis could be detected. Also, a 6.1 Kb RNA is present in female adults but not in 5th instar male nymphs. Therefore, cDNAs from female adult and 5th instar male fat bodies were used for differential screening of a female fat body cDNA library leading to the isolation of several female specific clones. All the clones hybridizing to the female specific 6.1 Kb RNA species were identical. We also describe the construction of new expression vectors, pGex-A and pGex-B, derived from the previously described plasmid pGex-1N. The new vectors, together with pGex-3X, comprise a set of expression plasmids with cloning sites in all three possible reading frames that give a fusion polypeptide with the glutathione S-transferase. This carrier protein can be cleaved by digestion with factor Xa in all three plasmids; one of the Vg cDNA clones was subcloned in pGex-A. Antibodies affinity purified from the fusion protein Vg/glutathione S-transferase recognized both large Vg subunits, suggesting an antigenic relationship between them. Furthermore, the small Vg subunits were not recognized, indicating that they may be localized at the N-terminal region of Vg precursors.

The boll weevil vitellogenin gene: nucleotide sequence, structure, and evolutionary relationship to nematode and vertebrate vitellogenin genes

Boll weevil (Anthonomus grandis) eggs contain two yolk proteins, YP47 and YP160. Using anti-YP160 antiserum as probe, a partial-length complementary DNA (cDNA) was isolated from a lambda gt11 adult female cDNA library. A second partial-length cDNA was isolated from a lambda gt10 adult female cDNA library by differential screening with male vs. female cDNAs. Northern blot analysis showed that each cloned cDNA hybridized to a 6-kb female-specific transcript. These cDNAs were used to probe a genomic library, and two overlapping genomic clones were obtained that span the boll weevil vitellogenin gene. The entire transcription unit was sequenced, and introns were mapped by a combination of primer extension experiments, S1 nuclease protection experiments, and polymerase chain reaction-mediated synthesis of two additional cDNA clones. Based on these data, the vitellogenin mRNA is 5511 nucleotides [plus a poly(A) tail of undetermined length] and specifies a provitellogenin of 1790 amino acids. The deduced protein has a Glu+Gln content of 16.3%, which is a relatively high value that is typical of most vitellogenins. Protein sequence similarities including Cys clusters conserved between boll weevil vitellogenin and Xenopus laevis A2 or Caenorhabditis elegans vit-5 vitellogenins indicated that the boll weevil protein is a member of the ancient nematode-vertebrate vitellogenin family. Moreover, the six introns in the boll weevil vitellogenin gene interrupt the coding region at positions closely or exactly corresponding to a subset of the positions of the 34 vertebrate vitellogenin introns, further supporting the argument for a common evolutionary relationship. This report represents the first complete nucleotide sequence and structural analysis of a nondipteran insect vitellogenin gene.

The genome of the Mediterranean fruitfly Ceratitis capitata: localization of molecular markers by in situ hybridization to salivary gland polytene chromosomes

We hybridized cloned DNA segments to salivary gland polytene chromosomes of the medfly, Ceratitis capitata, and thus established molecular markers for 24 sites on 6 out of 10 autosomal arms. An additional marker identified a medfly repetitive element that hybridizes to approximately 100 autosomal sites as well as a granular network that is thought to represent the X chromosome. Some of the markers correspond to 9 characterized transcription units, while 17 remain anonymous; at least 3 of the latter are restriction fragment length polymorphism (RFLP) markers. The characterized transcription units document that chromosomal arm 5L of C. capitata is homologous to the Drosophila melanogaster X chromosome, in agreement with previous inferences based on the extensive conservation of linkage groups in Diptera.

A cluster of vitellogenin genes in the Mediterranean fruit fly Ceratitis capitata: sequence and structural conservation in dipteran yolk proteins and their genes

Four genes encoding the major egg yolk polypeptides of the Mediterranean fruit fly Ceratitis capitata, vitellogenins 1 and 2 (VG1 and VG2), were cloned, characterized and partially sequenced. The genes are located on the same region of chromosome 5 and are organized in pairs, each encoding the two polypeptides on opposite DNA strands. Restriction and nucleotide sequence analysis indicate that the gene pairs have arisen from an ancestral pair by a relatively recent duplication event. The transcribed part is very similar to that of the Drosophila melanogaster yolk protein genes Yp1, Yp2 and Yp3. 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. Comparison of the five polypeptide sequences shows extensive homology, with 27% of the residues being invariable. The sequence similarity of the processed proteins extends in two regions separated by a nonconserved region of varying size. Secondary structure predictions suggest a highly conserved secondary structure pattern in the two regions, which probably correspond to structural and functional domains. The carboxy-end domain of the C. capitata proteins shows the same sequence similarities with triacyglycerol lipases that have been reported previously for the D. melanogaster yolk proteins. Analysis of codon usage shows significant differences between D. melanogaster and C. capitata vitellogenins with the latter exhibiting a less biased representation of synonymous codons.

Vitellogenesis in Drosophila: sequestration of a yolk polypeptide/invertase fusion protein into developing oocytes

The mechanism of yolk deposition into developing oocytes of Drosophila was investigated by following the fate of a reporter protein fused to a vitellogenin, or yolk polypeptide (YP). 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. RNA hybridization experiments with established lines of transformed flies showed that the hybrid gene was expressed in female fat bodies and ovaries but not in any male cells. Immunoblotting and endoglycosidase digestion showed that the hybrid protein was secreted from fat body cells via the secretory pathway, transported in hemolymph, and sequestered into developing oocytes. Transfusion experiments with hemolymph and pure invertase showed that sequestration of invertase depended on its attachment to YP. Immunocytochemistry demonstrated that the hybrid protein became localized in yolk granules as oocytes developed. Females homozygous for the fusion gene are generally sterile; their eggs containing the hybrid protein often collapse and their embryos fail to develop, suggesting that the structure of the yolk polypeptides is important for embryonic development. These experiments show that YP2 carries structural information sufficient to direct a reporter protein from fat body cells, through the hemolymph, and into the yolk granules of developing oocytes. This work provides a means of identifying the features of yolk polypeptides that are responsible for their deposition into yolk during oogenesis.

The amino-terminal sequence of lobster fibrinogen reveals common ancestry with vitellogenins

The amino-terminal sequence of lobster "fibrinogen" was determined. A computer search of the sequence revealed that the lobster protein is homologous to vitellogenins (precursors of egg-yolk proteins).

The nucleotide sequence of a microvitellogenin encoding gene from the tobacco hornworm, Manduca sexta

A microvitellogenin (mVg)-coding gene (mvg) has been isolated from a lambda phage library prepared from the tobacco hornworm, Manduca sexta. One of the lambda clones had a 15-kb insert and contained the entire mvg gene. A DNA fragment (3.0 kb) containing this mvg gene has been sequenced. Southern blot analysis showed that there may be more than one mvg gene in M. sexta. The putative transcriptional start point (tsp) for the cloned mvg was determined by primer extension analysis. This gene contains a single intron in the 5'-noncoding region. The 5'-flanking sequence was compared to the 5'-conserved regions of yolk polypeptide-encoding genes (yp) of Drosophila melanogaster. Two regions were found in the 5'-flanking sequence of the mvg gene that have 66% similarity to the D. melanogaster yp consensus sequence that is believed to be involved in gene expression controlled by ecdysteroids. Furthermore, the sequences flanking these two regions are also similar to the ecdysone-responsive elements found in several genes of D. melanogaster. In fact, preliminary experiments showed that mVg mRNA synthesis is induced by the 20-hydroxyecdysone. Four regions of the mvg gene resemble the upstream conserved regions of the two vitellogenin-encoding genes of the locust, Locusta migratoria. The nucleotide sequence of mvg has 70% similarity to the sequence of one or more of the 30-kDa hemolymph proteins of Bombyx mori. This indicates a very close evolutionary relationship between these proteins.

Homology of Drosophila yolk proteins and the triacylglycerol lipase family

Drosophila yolk proteins consist of a set of related proteins of 50,000 Mr. They are derived from slightly larger precursors by cleavage of a signal peptide. In this respect, they differ from the yolk proteins of other insects which are proteolytic fragments of precursors of 200,000 Mr or larger, termed vitellogenins and probably homologous to the vitellogenins of other egg-laying species. We report here a comparative amino acid analysis demonstrating that the Drosophila yolk proteins are non-homologous to the vitellogenin group of yolk proteins, but surprisingly are related to the triacylglycerol lipase family.

A single gene encoding vitellogenin in the sea urchin Strongylocentrotus purpuratus: sequence at the 5' end

The synthesis of vitellogenin (yolk protein precursor) in the sea urchin, Strongylocentrotus purpuratus, is unique in that both males and females produce a high level of the protein. In this paper we show that this organism also is unique in possessing only a single vitellogenin gene. Like the genes that encode analogous proteins in vertebrates, the sea urchin gene is large, about 19 kb in length. The sequence surrounding the 5' end of the gene revealed several other similarities to vertebrate vitellogenin genes: the signal sequence is exceptionally short and has a sequence similar to those from frog and chick; there is a canonical TATA box at -32; and there is a sequence closely resembling the estrogen-responsive element at -207.

Vertebrate and nematode genes coding for yolk proteins are derived from a common ancestor

One of the most obvious characteristics of the egg cells of oviparous animals is their large size resulting to a major extent from the deposition of nutritional reserves, mainly constituted of yolk proteins. In general, these are derived from a precursor called vitellogenin, which undergoes posttranslational modifications during secretion and during transport into and storage within the oocytes. Comparative analysis of the structural organization of the vitellogenin gene and of its product in different species shows that the vitellogenin gene is very ancient and that in vertebrates the gene may have more resemblance to the earliest gene than in invertebrates.