Refolding and characterization of recombinant human soluble CTLA-4 expressed in Escherichia coli

CD28 and CTLA-4 are homologous cell surface proteins expressed by T cells. CD28 is constitutively expressed by most T cells, whereas CTLA-4 is expressed by activated T cells. Both proteins are ligands for the costimulatory molecules CD80 and CD86 expressed by activated B cells, macrophages, and dendritic cells. A fusion protein comprising the CTLA-4 extracellular domain joined to a human immunoglobulin heavy chain constant region (CTLA4Ig) binds CD80 and CD-86 with high affinity and inhibits CD80/CD86-dependent immune responses in vitro and in vivo. Attempts at producing the CTLA-4 extracellular domain as an unfused protein have met with limited success. Here we describe the expression and purification of the CTLA-4 extracellular domain as a nonfused protein in Escherichia coli. The 12.5-kDa CTLA-4 extracellular domain was insoluble when expressed in E. coli and required denaturation, reduction, and refolding steps to become soluble and assume its proper conformation. The protein refolded into a mixture of monomers, disulfide-linked dimers, and higher order disulfide-linked aggregates. sCTLA-4 dimers were the predominant refold form when air was used as the oxidizing agent during the refold procedure. Purified sCTLA-4 dimers were 10- to 50-fold more potent than sCTLA-4 monomers at inhibiting T cell activation using a CD80-dependent in vitro bioassay.

Polyethylene glycol conjugated insulin-like growth factor binding protein-1 (IGFBP-1) inhibits growth of breast cancer in athymic mice

Insulin-like growth factor (IGF) binding protein-1 (BP-1) inhibits IGF-mediated proliferation of some breast cancer cell lines in vitro. Here we examined whether recombinant human wild-type IGFBP-1 (WT-BP-1) and IGFBP-1 conjugated with polyethylene glycol (PEG-BP-1) could inhibit breast cancer growth. Three breast cancer cell lines were used: MCF-7, MDA-MB-231 and MDA-MB-435A (ascites model). The cells were grown in agar with or without the BP-1 conjugates to investigate their effect on colony formation. Both WT-BP-1 and PEG-BP-1 inhibited anchorage-independent growth (AIG) of MCF-7 and MDA-MB-435A cells. AIG of MDA-MB-231 cells was not inhibited by PEG-BP-1, whereas WT-BP-1 significantly stimulated colony number. We also tested both forms of BP-1 in xenograft tumour models. Two solid breast tumour models were studied using MCF-7 and MDA-MB-231 cell lines, and one ascites model using the MDA-MB-435A cell line. PEG-BP-1 inhibited malignant ascites formation in the MDA-MB-435A model. Conversely, PEG-BP-1 did not significantly inhibit MCF-7 xenograft growth. However, the MDA-MB-231 tumour growth curves were significantly different by a constant amount, suggesting that PEG-BP-1 treatment inhibited early tumour growth of this cell line. In contrast, WT-BP-1 was ineffective in the MDA-MB-231 tumours. These data show that anti-IGF strategies can be used to inhibit breast cancer cell growth. Since PEG-BP-1 inhibited the in vivo, but not in vitro, growth of MDA-MB-231, we speculate that PEG-BP-1 may block host IGF functions required for optimal tumorigenesis. Because PEG-BP-1 has a prolonged serum half-life compared to WT-BP-1, we conclude that improvements in BP-1 pharmacological properties enhanced its antitumour effects in vivo.

Pharmacokinetic profile of recombination human insulin-like growth factor binding protein-1 in athymic mice

Neutralization of insulin-like growth factor action by insulin-like growth factor binding protein-1 inhibits the in vitro growth of breast cancer cells. We performed this study to determine the pharmacokinetic profile of recombinant human IGFBP-1 (rhIGFBP-1) in athymic mice as a prelude to testing this protein in a human tumor xenograft model. After the subcutaneous injection of 1 mg, rhIGFBP-1 migrating at 29 kDa could be detected by ligand blotting and immunoblotting. Plasma concentrations of rhIGFBP-1 were quantified by immunoassay and demonstrated a half-life was 2.49 hours with the maximal concentration of 43.5 micrograms/mL occurring at 1 hour. The area under the concentration-time curve was 78.32 micrograms x hr/mL. Plasma clearance was 12.77 mL/hr and the mean residence time was 1.96 hours. rhIGFBP-1 was also detected in some tissues and was also cleared rapidly. These results show that high plasma and tissue levels of rhIGFBP-1 can be obtained after subcutaneous injection in athymic mice, however, the short half-life of the protein may limit its therapeutic use.

Cloning and characterization of a human type II receptor for bone morphogenetic proteins

Bone morphogenetic proteins (BMPs) are members of the transforming growth factor beta superfamily. Several members of this family have been shown to transduce their signals through binding to type I and type II serine-(threonine) kinase receptors. Here we report the cDNA cloning and characterization of a human type II receptor for BMPs (BMPR-II), which is distantly related to DAF-4, a BMP type II receptor from Caenorhabditis elegans. In transfected COS-1 cells, osteogenic protein (OP)-1/BMP-7, and less efficiently BMP-4, bound to BMPR-II. BMPR-II bound ligands only weakly alone, but the binding was facilitated by the presence of previously identified type I receptors for BMPs. Binding of OP-1/BMP-7 to BMPR-II was also observed in nontransfected cell lines. Moreover, a transcriptional activation signal was transduced by BMPR-II in the presence of type I receptors after stimulation by OP-1/BMP-7.

Effects of insulin-like growth factor-I and insulin-like growth factor binding protein-1 on wound healing in a dermal ulcer model

The effects on wound healing of insulin-like growth factor-I with and without insulin-like growth factor binding protein-1 were studied in a rabbit ear dermal ulcer model under both nonischemic and ischemic conditions. Wounds 6 mm in diameter were made on the ventral surface of rabbit ears for a total of 272 wounds in the nonischemic group and 77 wounds in the ischemic group. Insulin-like growth factor-I in varying doses (1 to 43 microg) and in combination with varying molar ratios of the binding protein were added at time of wounding to each wound. Wounds were analyzed histomorphometrically on day 7 after wounding. We found that insulin-like growth factor-I or binding protein alone at varying doses did not have any effects on wound healing parameters. Low to moderate doses (1 microg and 4 microg, respectively) of the combination of insulin-like growth factor-I with the binding protein in a molar ratio of 5:1 or 11:1 showed a 52% increase (p < 0.05) in new granulation tissue in the nonischemic model compared with controls but did not significantly augment new granulation tissue formation in the ischemic wound model. A high dose (43 microg) at a 10:1 molar ratio of growth factor to binding protein was required to elicit significantly enhanced wound healing in ischemic wounds. These results indicate that insulin-like growth factor binding protein-1 modulates the effects of insulin-like growth factor-I in promoting wound healing in vivo and that the combination is a highly effective vulnerary compound with effects comparable in magnitude with other growth factors previously tested in this model.

Co-administration of insulin-like growth factor (IGF)-I and IGF-binding protein-1 stimulates wound healing in animal models

The stimulatory effect of recombinant human insulin-like growth factor-I (rhIGF-I) and recombinant human insulin-like growth-factor-binding protein-1 (rhIGFBP-1) on wound healing was assessed using diabetic db/db mice and normal rabbits. Full-thickness wounds of 6 mm diameter were prepared on the backs of diabetic C57BL/KsJ db/db mice and on the inner sides of normal rabbit ears. Various concentrations of rhIGF-I and/or rhIGFBP-1 were applied locally to the open wounds of db/db mice once daily for 5 d and to the covered wounds of normal rabbits once after wounding. Sections of the wounds were evaluated histologically on the seventh or eighth day by measuring re-epithelialization (%), area of granulation tissue (mm2), and capillary numbers. Wound repair was accelerated by each of the treatments in descending order of rhIGF-I plus rhIGFBP-1, rhIGF-I, rhIGFBP-1, and vehicle alone. In db/db mice, the combination of 50 micrograms rhIGF-I and 165 micrograms rhIGFBP-1 (equimolar ratio) significantly stimulated granulation tissue formation (p < 0.01) and capillary numbers (p < 0.05). Doses of rhIGFBP-1 greater than 16.5 micrograms were required for significant acceleration of the healing stimulated by 50 micrograms of rhIGF-I. In normal rabbits, co-administration of 10 micrograms rhIGF-I and 33 micrograms rhIGFBP-1 (equimolar ratio) significantly stimulated all three wound-healing parameters (p < 0.01), with such stimulation being much greater than that induced by rhIGF-I alone. Interestingly, rhIGFBP-1 alone showed a mild stimulatory activity on wound healing in both models despite its lack of mitogenic activity in vitro. These results demonstrate that rhIGFBP-1 enhances the stimulatory activity of rhIGF-I on wound healing and suggest the clinical utility of the co-administration of rhIGF-I and rhIGFBP-1 for wound repair.

Recombinant human insulin-like growth factor (IGF)-binding protein-1 inhibits somatic growth stimulated by IGF-I and growth hormone in hypophysectomized rats

We have examined the effects of exogenously administered recombinant human insulin-like growth factor-binding protein-1 (rhIGFBP-1) alone and in combination with recombinant human insulin-like growth factor-I (rhIGF-I) or human GH on weight gain and tibial epiphysis enlargement in hypophysectomized rats. rhIGF-I, given twice daily by sc injection, increased both growth parameters in a dose-dependent manner. Coadministration of increasing amounts of rhIGFBP-1 with a constant amount of rhIGF-I (80 micrograms/injection, given twice daily) resulted in a dose-dependent inhibition of the growth-promoting effects of rhIGF-I. A rhIGFBP-1 dose of 9.8 micrograms/injection (an IGFBP-1/IGF-I molar ratio of 0.04:1) caused no significant effect on rhIGF-I-stimulated growth parameters, whereas a rhIGFBP-1 dose of 1200 micrograms/injection (IGFBP-1/IGF-I molar ratio of 5:1) resulted in 78% or greater inhibition of rhIGF-I-stimulated growth (P < 0.05). rhIGFBP-1 doses of 48 and 240 micrograms/injection (IGFBP-1/IGF-I molar ratios of 0.2:1 and 1:1, respectively) had intermediate inhibitory effects. None of the rhIGFBP-1 doses potentiated the growth-promoting effects of rhIGF-I. Rats treated with rhIGFBP-1 alone (twice daily injections of 9.8, 48, 240, or 1200 micrograms) showed no significant differences in growth parameters compared to rats treated with vehicle. Coadministration of rhIGFBP-1 (1200 micrograms/injection, given twice daily) with GH (15 mU/injection, given twice daily) inhibited weight gain and tibial epiphysis enlargement stimulated by GH by at least 50% in each of two experiments (P < 0.05). These studies demonstrate that nonphosphorylated rhIGFBP-1 can inhibit the growth-promoting effects of rhIGF-I and GH in vivo. The results suggest that in addition to its proposed role in glucose homeostasis, IGFBP-1 may play a role in inhibiting somatic growth and other physiological functions stimulated by IGF-I and GH.

Isolation of putative cysteine protease genes of Ostertagia ostertagi

Recombinant phage containing putative Ostertagia ostertagi cysteine protease genes have been isolated from a lambda EMBL-3:genomic DNA library using a Haemonchus contortus cathepsin B-like cysteine protease cDNA as hybridization probe. Restriction enzyme maps of the phages suggest that they identify at least 3 genes, 2 of which appear to be linked in tandem. The complete nucleotide sequence of one gene, CP-1, was determined. The CP-1 gene appears to be organized into 12 exons than span 4.5 kb of DNA. The number and sizes of the exons are essentially identical to those in the H. contortus AC-2 cysteine protease gene. Partial nucleotide sequences obtained for a second O. ostertagi gene, CP-3, revealed a similar organization for exons 8-12 in this gene. Like other cathepsin B-like cysteine proteases, CP-1 appears to be synthesized initially as a preproprotein that is proteolytically processed to its mature form. The amino acid identity between the presumptive CP-1 and CP-3 proteins is 66%, which is similar to the level of homology between the presumed mature protein regions of CP-1 and AC-2. Amino acid identity between CP-1 and AC-2 is greatest in the mature protein region and lowest in the signal sequence and propeptide regions. The CP-3 protein appears to be most closely related to the H. contortus AC-5 protein. CP-1 and CP-3 display significantly greater homology to H. contortus cysteine proteases than they do to human cathepsin B or the Sm31 cysteine protease of Schistosoma mansoni (about 40% identity with each).

Fibrinogen-degrading proteins from Haemonchus contortus used to vaccinate sheep

Sixteen nonsibling sheep, approximately 12 months old, that were raised in a helminth-free environment, were used for 2 protection studies 6 months apart. Sheep were vaccinated weekly for 5 weeks by IM injection of fibrinogen-degrading proteins derived from the intestinal tract of adult Haemonchus contortus. Ten days after the last vaccination, sheep were given 2,500 infective H contortus larvae by intraruminal injection. Vaccinated sheep produced specific antibodies, and were protected from the worm challenge. Significant differences in mean fecal worm egg counts for 56 days after worm challenge, in mean numbers of H contortus worms, and female fecundity ratios at necropsy were detected in vaccinated sheep, compared with those in control sheep. These data suggest that the fibrinogen-degrading proteins have a protective role in vaccination of sheep against H contortus.

Cloning and sequence comparisons of four distinct cysteine proteases expressed by Haemonchus contortus adult worms

Three new members of a developmentally regulated cysteine protease gene family of the parasitic nematode Haemonchus contortus have been isolated and characterized. One of the new genes, AC-3, was found to be linked in tandem to the previously characterized AC-2 gene. Nucleotide sequence analyses revealed that the first 90 amino acids of AC-3 are organized into four exons, similar to the situation in AC-2. A cDNA that appears to be a near full-length copy of the AC-3 gene was isolated using the polymerase chain reaction (PCR) technique to amplify cDNAs from adult worm poly(A)+ mRNAs. In addition to AC-3, a distinct cysteine protease cDNA, AC-4, was amplified by the same oligonucleotide primers. cDNAs encoding a fifth cysteine protease, AC-5, were isolated from an adult worm cDNA expression library using specific rabbit antisera and by PCR. Comparison of the predicted amino acid sequences of AC-3, AC-4 and AC-5 reveal that they share 64-77% identity with one another and with the previously reported AC-1 and AC-2 sequences. The amino acids surrounding the active site cysteine are highly conserved, as are the positions of other cysteine residues in the mature protein sequences. The H. contortus proteases are more similar to one another than they are to human cathepsin B (38-44% amino acid identity) or to the Sm31 cysteine protease of Schistosoma mansoni (36-40% identity). Our studies indicate that H. contortus adult worms express mRNAs for several distinct cysteine proteases. The significant primary sequence differences between the proteases suggest that they differ in their substrate specificities and precise physiological functions.

Molecular and biochemical aspects of nematode collagens

Collagens are major structural proteins of nematode cuticles and basement membranes (basal laminae). The collagen proteins that form these structures differ in their biochemical and physical properties and are encoded by distinct gene families. Nematode basement membrane collagens are large proteins that show strong homology to basement membrane collagens of vertebrates. There appear to be 2 nonidentical basement membrane collagen genes in nematodes. Cuticle collagens are about one-sixth the size of basement membrane collagens and are encoded by a large family of 20-150 nonidentical genes. Cuticle collagens can be subdivided into 4 families based upon certain structural features in the proteins. The mature, extracellular forms of both types of collagen proteins are extensively cross-linked by disulfide bonds and are largely insoluble in the absence of a thiol-reducing agent. Cuticle collagens also are cross-linked by nonreducible covalent bonds that involve tyrosine residues. The experimental studies that have led to our current understanding of the structures of basement membrane and cuticle collagens are reviewed. Some previous questions about the physical properties of these proteins are reexamined in light of the primary sequence information now available for the proteins.

Protective studies in sheep immunized with cuticular collagen proteins and peptides of Haemonchus contortus

Twenty-eight nonsibling sheep aged approximately 12 months and raised in a helminth-free environment were used in two protection studies. Immunizations were conducted by two intramuscular injections 30 days apart with a synthetic 18AA cuticle collagen peptide and native cuticle collagens derived from the third- and fourth-stage larvae of Haemonchus contortus. Ten days following the last immunization, the sheep were each given 500 infective H. contortus larvae per day for five consecutive days by intraruminal injection. Both collagen materials induced antibodies reactive with cuticle collagens; however, neither induced reproducible protection to H. contortus infections in vaccinated/infected sheep. In the most extensive test, there were no statistical differences in mean faecal worm egg count for 56 days post worm challenge, in mean numbers of H. contortus and female fecundity ratios at necropsy of immunized and unimmunized sheep. Failure to reproducibly immunize sheep with cuticle collagens may be due to the inability of antibodies or host immune cells to reach the collagen epitopes in the nematode cuticle without prior surface coat removal as postulated in human nematode studies.

A developmentally regulated cysteine protease gene family in Haemonchus contortus

The nucleotide sequence of a gene encoding a 35-kDa thiol protease of the parasitic nematode Haemonchus contortus has been determined. The gene, designated AC-2, shares 97% nucleotide sequence identity and 98% amino acid identity with previously characterized AC-1 cDNAs encoding the thiol protease. The AC-2 gene spans 8 kb and appears to contain 11 introns, ranging in size from 57 bp to over 5.2 kb. One of the introns interrupts the proposed active site region that is conserved between the H. contortus protease and the related thiol proteases cathepsin B and papain. Southern blot hybridization experiments indicate that the protease is encoded by a small gene family in H. contortus. Rabbit antisera prepared against the recombinant protein react on Western blots with 35 and 37-kDa proteins of adult worms. These proteins were not detectable by Western blot analysis in three larval parasitic developmental stages of H. contortus. Northern blot hybridizations indicate that mRNA transcripts for the gene family are present at low levels in a mixed population of third- and fourth-stage larvae but highly abundant in adult worms. Expression of the protease correlates with blood-feeding and suggests a role for the protease in blood digestion.

Molecular cloning and primary sequence of a cysteine protease expressed by Haemonchus contortus adult worms

We have cloned cDNAs encoding a 35-kilodalton cysteine protease that is a major component of protective extracts isolated from blood-feeding Haemonchus contortus adult worms. Near full-length cDNAs for the protease were isolated by immunoscreening an adult worm cDNA expression library with a rabbit antiserum prepared against the protein eluted from preparative SDS gels and by rescreening the library with oligonucleotide probes. The protein predicted from the nucleotide sequence of the cDNAs and of a genomic DNA clone comprises 342 amino acids and contains an N-terminal signal sequence, 16 cysteine residues and four potential N-linked glycosylation sites. The enzyme appears to be glycosylated in vivo. The H. contortus protease, called AC-1, displays an overall 42% sequence identity with the human lysosomal thiol protease cathepsin B. The similarities between cathepsin B and AC-1 are localized primarily to regions of cathepsin B that comprise the mature, active form of the enzyme. A stretch of six amino acids that includes the active site cysteine of cathepsin B is conserved, and is present in the same relative location in AC-1, suggesting that this region comprises the active site of the H. contortus enzyme.

Haemonchus contortus: a simple procedure for purifying surface proteins from third- and fourth-stage larvae

Surface proteins were solubilized from exsheathed third (XL3)- and fourth (L4)-stage larvae of Haemonchus contortus by a one-step extraction procedure involving brief heat treatment of the worms in the presence of buffer and 100 mM sodium chloride. Surface proteins also could be preferentially extracted from XL3s, but not from L4s, by heating the worms briefly in 1% sodium dodecyl sulfate. The major proteins extracted by these procedures were similar in molecular weight to those detected by surface-labeling live worms with 125Iodine. Both extraction procedures solubilized a single, major protein with an apparent molecular weight of 68-97 kDa from XL3s. In contrast, extraction of L4s with 100 mM sodium chloride yielded four major proteins with relative molecular weights of 27, 29, 78, and 200 kDa. Antibodies raised in rabbits to surface proteins prepared by the sodium chloride procedure reacted with the surfaces of live worms in indirect immunofluorescence assays. The anti-XL3 surface protein serum was stage specific in immunofluorescence experiments using live worms and in immunoprecipitation experiments using 125Iodine-labeled XL3 and L4 surface proteins. The overall amino acid composition of the surface proteins is hydrophilic. Twenty-six percent of the amino acid residues of the XL3 surface proteins, which consist predominantly of the 68-97 kDa species, are glutamate or glutamine.

Cuticle collagen genes of Haemonchus contortus and Caenorhabditis elegans are highly conserved

Several genes and partial cDNAs encoding cuticle collagens have been isolated from the sheep parasitic nematode Haemonchus contortus. DNA sequencing and Southern blot hybridization studies reveal that H. contortus collagens comprise a large family of related, but non-identical genes. The genes appear to be dispersed throughout the genome. The predominant size of collagen mRNA in molting worms was found to be between 1.0 and 1.2 kb. The one complete gene that was sequenced contains two short introns and encodes a protein of about 300 amino acids. The predicted protein sequence contain several (Gly-X-Y)n triple helix-coding domains that are interrupted by short stretches of non-helix-coding amino acids. The size of the predicted protein and the organization of the triple-helix coding domains are similar to that of Caenorhabditis elegans collagens. All the H. contortus genes studied show a striking homology to the C. elegans collagen gene subfamily represented by col-1. In particular, the amino acid sequence of the carboxy-terminal non-(Gly-X-Y)n region and the positions of cysteine residues flanking the (Gly-X-Y)n domains were found to be highly conserved in the collagens of these two nematodes.

Identification and preliminary characterization of cuticular surface proteins of Haemonchus contortus

Cuticular surface antigens of the XL3 and L4 stages of Haemonchus contortus have been studied by surface labeling and immunological techniques. Live worms were labeled with 125I and extracted with sodium dodecyl sulfate (SDS) followed by SDS + 2-mercaptoethanol. The SDS-soluble surface proteins of XL3s and L4s were found to consist of relatively few major species. The pattern of labeled polypeptides was distinctive for each developmental stage. These proteins are refractory to digestion by bacterial collagenase. Several of the proteins are glycosylated. Further extraction of labeled worms with SDS + 2-mercaptoethanol solubilized additional labeled proteins that appeared to be primarily collagens. Rabbit antisera prepared against native XL3 and L4-cuticles reacted strongly with the surfaces of live worms in immunofluorescence assays. In contrast, antisera prepared against SDS-extracted cuticles reacted weakly or not at all with live worms in similar experiments. Rabbit antisera prepared against adult cuticles failed to react with live XL3s or L4s. These studies suggest that the major surface antigens of XL3s and L4s are solubilized by SDS and that there are different antigens present on the cuticular surfaces of XL3s, L4s and adults. Stage-specificity in cuticular surface proteins may contribute to the successful parasitic lifestyle of this nematode.

Sequence comparisons of developmentally regulated collagen genes of Caenorhabditis elegans

Collagen genes col-6, col-7 (partial), col-8, col-14 and col-19 from the nematode Caenorhabditis elegans were sequenced, and compared to the previously sequenced genes col-1 and col-2. The genes are between 1.0 and 1.2 kb in length, and each includes one or two short introns. The presumptive promoter regions contain sequences similar to the eukaryotic TATA promoter element. Two distinct, conserved sequences were found in the presumptive promoter regions of, respectively, the dauer larva-specific genes col-2 and col-6, and the primarily adult-specific genes col-7 and col-19. The domain structures of the collagen polypeptides are similar: each polypeptide contains two triple-helix forming (Gly-X-Y)n domains, one of 30-33 amino acids (aa), and the other of 127-132 aa. The latter domain is interrupted by one to three short (2-8 aa) non-(Gly-X-Y)n segments that occur at relatively conserved locations in each polypeptide. Sets of cysteine residues flank the (Gly-X-Y)n domains in all of the polypeptides. The genes can be placed into three families based upon amino acid sequence similarities. Genes within a family do not always exhibit similar developmental expression programs, suggesting that structural and regulatory regions of the genes have evolved separately. The codon usage in the genes is highly asymmetrical, with adenine appearing in the third position of 85% of the glycine codons, and 93% of the proline codons.

Genetic mapping of Caenorhabditis elegans collagen genes using DNA polymorphisms as phenotypic markers

In Caenorhabditis elegans collagens comprise a dispersed family of 40-150 genes, the majority of which probably code for collagen proteins found in the animal's cuticle. The conserved (Gly-X-Y)n triple helix coding sequence of collagen genes has facilitated the isolation of a large number of C. elegans collagen genes by recombinant DNA methods. We have begun a study of the chromosomal organization of these genes by screening laboratory strains of C. elegans for DNA polymorphisms in the regions surrounding collagen genes. Polymorphisms near seven genes have been identified and have been used as phenotypic markers in genetic crosses to assign the genes to linkage groups II, III, IV, and X. Four genes are shown by multifactor crosses to map to a 2-3 map unit interval between unc-24 and unc-22 on chromosome IV.

Expression of the Caenorhabditis elegans collagen genes col-1 and col-2 is developmentally regulated

The total collagen gene expression as well as the specific expression of two sequenced Caenorhabditis elegans collagen genes, col-1 and col-2, has been investigated. Northern blots of RNA isolated from animals at different developmental stages were probed under conditions that allow cross-hybridization of all collagen sequences. The majority of hybridization is to transcripts of 1.1-1.4 kilobases (kb) in length, with weak hybridization to some larger transcripts. Different size patterns, within the 1.1-1.4-kb ranges, are seen in RNAs from different developmental stages. Gene-specific probes were produced from the C. elegans collagen genes col-1 and col-2, and each was shown to hybridize to a single size transcript in the 1.1-1.4-kb region. The col-1 transcript was found in all the developmental stages examined, but its abundance varied between stages. The col-2 transcript was detected only in a single developmental stage, during formation of the dauer larvae. The 5' and the 3' ends of the col-1 and col-2 transcripts were determined by S1 nuclease digestion experiments. Both genes have the common "TATA" and "CAAT" box sequences preceding the 5' end of their transcripts and there is strong sequence homology in their 5' untranslated regions. Multiple copies of an eight-nucleotide repeat sequence were found upstream from both col-1 and col-2.

Number and organization of collagen genes in Caenorhabditis elegans

We analyzed the number and organization of collagen genes in the nematode Caenorhabditis elegans. Genomic Southern blot hybridization experiments and recombinant phage library screenings indicated that C. elegans has between 40 and 150 distinct collagen genes. A large number of recombinant phages containing collagen genes were isolated from C. elegans DNA libraries. Physical mapping studies indicated that most phage contained a single small collagen gene less than 3 kilobases in size. A few phage contained multiple collagen hybridizing regions and may contain a larger collagen gene or several tightly linked small collagen genes. No overlaps were observed between phages containing different collagen genes, implying that the genes are dispersed in the C. elegans genome. Consistent with the small size of most collagen genes, we found that the predominant class of collagen mRNA in C. elegans is 1.2 to 1.4 kilobases in length. Genomic Southern blot experiments under stringent hybridization conditions revealed considerable sequence diversity among collagen genes. Our data suggest that most collagen genes are unique or are present in only a few copies.

Comparisons of the complete sequences of two collagen genes from Caenorhabditis elegans

Several collagen genes have been isolated from the nematode Caenorhabditis elegans. The complete nucleotide sequences of two of these genes, col-1 and col-2, have been determined. These collagen genes differ from vertebrate collagen genes in that they contain only one or two introns, their triplehelical regions are interrupted by nonhelical amino acid sequences and they are smaller. A high degree of nucleotide and amino acid homology exists between col-1 and col-2. In particular, the regions around cysteines and lysines are most highly conserved. The C. elegans genome contains 50 or more collagen genes, the majority of which probably encode cuticle collagens; col-1 and col-2 apparently are members of this large family of cuticle collagen genes.

Cuticle of Caenorhabditis elegans: its isolation and partial characterization

The adult cuticle of the soil nematode, Caenorhabditis elegans, is a proteinaceous extracellular structure elaborated by the underlying layer of hypodermal cells during the final molt in the animal's life cycle. The cuticle is composed of an outer cortical layer connected by regularly arranged struts to an inner basal layer. The cuticle can be isolated largely intact and free of all cellular material by sonication and treatment with 1% sodium dodecyl sulfate (SDS). Purified cuticles exhibit a negative material in the basal cuticle layer. The cuticle layers differ in their solubility in sulfhydryl reducing agents, susceptibility to various proteolytic enzymes and amino acid composition. The struts, basal layer, and internal cortical layer are composed of collagen proteins that are extensively cross-linked by disulfide bonds. The external cortical layer appears to contain primarily noncollagen proteins that are extensively cross-linked by nonreducible covalent bonds. The collagen proteins extracted from the cuticle with a reducing agent can be separated by SDS-polyacrylamide gel electrophoresis into eight major species differing in apparent molecular weight.

GENETIC AND PHENOTYPIC CHARACTERIZATION OF ROLLER MUTANTS OF CAENORHABDITIS ELEGANS

Eighty-eight mutants of C. elegans that display a roller phenotype (a helically twisted body) have been isolated and characterized genetically and phenotypically. The mutations are located in 14 different genes. Most genes contain a number of alleles. Their distribution among the chromosomes appears nonrandom, with seven of the genes being located on linkage group 11, some very closely linked. The phenotypes of the mutants suggest that there are five different classes of genes, each class representing a set of similar phenotypic effects: Left Roller (four genes), Right Roller (one gene), Left Squat (one gene), Right Squat (two genes) and Left Dumpy Roller (six genes). The classes of mutants differ with respect to a number of characteristics that include the developmental stages affected and the types of aberrations observed in cuticle structure. A variety of gene interactions were found, arguing that these genes are involved in a common developmental process. The presence of alterations in cuticle morphology strongly suggests that these genes are active in the formation of the nematode cuticle.