Interaction of epidermal growth factor with micelles monitored by photochemically induced dynamic nuclear polarization-1H NMR spectroscopy

Photochemically induced dynamic nuclear polarization (CIDNP)-1H-NMR spectroscopy has been used to study the interaction of the protein hormone epidermal growth factor (EGF) with micelles of sodium dodecyl sulfate (SDS) and dodecylphosphorylcholine (DPC). Conventional 1H-NMR spectra show that most protein resonances remain unperturbed when micelles are added to solution, which argues that the overall protein conformation is maintained in the presence of SDS or DPC at the concentrations used. Photo-CIDNP enhancements of resonances assigned to aromatic side chains of residues at the COOH terminus and beta-sheet regions of murine EGF (i.e. Trp-49, Trp-50, and Tyr-37) are considerably reduced in the presence of micelles, while resonances of aromatic side chains of residues found elsewhere on the protein surface are mostly unaffected. This suggests that the primary interaction between murine EGF and the micelle occurs at the micelle-bulk solvent interface. The overall negatively charged surface of SDS micelles tends to induce a stronger interaction with the protein compared to the zwitterionic DPC micelles, probably due to electrostatic interactions. Cleavage of the COOH-terminal pentapeptide containing both tryptophan residues enhances the already present, but weak, interaction with Tyr-10 and attenuates it with Tyr-37. A similar interaction pattern is found with rat EGF suggesting that at least concerning these two species of EGF the interaction is somewhat specific and conserved. A simple mass-action model for protein-micelle interaction is also presented.     

Identification of amino acid residues critical for infection with ecotropic murine leukemia retrovirus.

The murine cationic amino acid transporter is also the receptor for murine ecotropic leukemia retrovirus (MuLV-E). Recently, we have cloned a human gene (H13) homologous to the murine ecotropic retroviral receptor (ERR). Although the human homolog is very similar to murine ERR in sequence (87.6% amino acid identity) and structure (14 transmembrane-spanning domains), the human protein fails to function as a receptor for MuLV-E. To identify amino acid residues critical for MuLV-E infection, we took advantage of this species difference and substituted human H13 and murine ERR amino acid residues. Mouse-human chimeric receptor molecules were generated by taking advantage of using common restriction sites. These studies demonstrated that extracellular domains 3 and/or 4 contain the critical amino acid residues. Oligonucleotide-directed mutagenesis was then used to create 13 individual ERR mutants containing one or two amino acids substitutions or insertions within these two extracellular domains. Substitution of as few as one amino acid residue (Tyr) at position 235 in ERR with the corresponding H13 amino acid residue Pro abrogates the ability to function as a receptor for MuLV-E infection. Conversely, substitution of just two amino acid residues at positions 240 and 242 or 242 and 244 in H13 with the corresponding amino acid residues in ERR endows H13 with the ability to function as the receptor. This observation can be utilized to significantly improve the safety of retrovirus-mediated gene therapy in humans.     

Sterilization of epidermal growth factor with supercritical carbon dioxide and peracetic acid; analysis of changes at the amino acid and protein level

Aseptic processing and terminal sterilization become increasingly challenging as medical devices become more complex and include active biologics. Terminal sterilization is preferred for patient safety and production costs. We aimed to determine how sterilization using supercritical CO₂ (scCO₂) with low levels of peracetic acid (PAA) affects amino acids and human epidermal growth factor (EGF) as a model protein. In a benchtop reactivity test, the amino acids methionine, tryptophan, arginine and lysine reacted with low levels of PAA in solution. At PAA levels used for scCO₂ sterilization, however, mass spectrometry only identified oxidative adducts on methionine and tryptophan. Mass spectrometry analysis of EGF exposed to scCO₂/PAA identified oxidative adducts on residues Met₂₁, Trp₄₉ and Trp₅₀, as well as a low level of truncations after residues Trp₄₉ and Trp₅₀. Importantly, processing of EGF in solution with scCO₂ did not affect its native conformation, and sterilized EGF maintained its activity in cell proliferation assays. When processing samples in lyophilized form with scCO₂/PAA, amino acids did not react with PAA and the presence of adducts was strongly reduced on methionine and tryptophan, both as single amino acids and in EGF. Truncation after tryptophan residues did not occur. EGF sterilized in the lyophilized form retained its activity when processing occurred with added moisture. These results have significant implications for the maintenance of biological function in sterilized decellularized scaffolds and the ability to manufacture terminally sterilized combination devices containing therapeutic peptides or proteins.     

Structure-function studies of mEGF: Probing the type Iβ-turn between residues 25 and 26

The interaction between epidermal growth factor (EGF) and its receptor molecule is not completely understood and has received much attention recently. Studies combining site-directed mutagenesis and NMR spectroscopy have identified a number of EGF residues that are required for activity and are believed to interact directly with the receptor. Instead of focusing on these residues, this study combines site-directed mutagenesis and NMR spectroscopy to probe the role of the type Iβ-bend located between residues 25 and 26 of the N-terminal subdomain of the protein. Ser25 of murine EGF is replaced by Pro in an attempt to stabilize this turn conformation to produce a variant of mEGF with increased activity relative to that for the native protein. Ser25 is also replaced by Ala, which is found at position 25 in human EGF (hEGF), as a more conservative replacement. Receptor binding studies demonstrate that both mutations produce about a 30% reduction in binding affinity, which is shown to result from local changes within the loop or minor perturbations of residues neighboring the loop rather than from long-range perturbations of theβ-sheet of the N-terminal subdomain. The type Iβ-turn appears to remain intact in both mutants; however, replacement with Pro seems to introduce more flexibility into this region of the protein. These results demonstrate that perturbation of thisβ-turn has little effect on EGF-receptor interactions.     

Isolation of multiple biologically and chemically diverse species of epidermal growth factor

We have analyzed several lots of epidermal growth factor (EGF) purified from murine submaxillary glands including "receptor grade" EGF from Collaborative Research and EGF from Boehringer Mannheim Biochemicals. New England Nuclear uses "receptor grade" EGF to produce 125I-labeled EGF. Though these reagents are reported to be homogeneous, we found them to be a mixture of six species. A method was developed to separate this mixture into its component parts. The individual components were chemically characterized and tested for biological potency. N-terminal sequence analysis of the unfractionated EGF-mixture reveals three different sequences starting with residues 1, 2, or 3 of the mature peptide. Each component exhibited different degrees of mitogenic and EGF receptor binding activity indicating that the N-terminal region contributes to the biological response. The species representing the complete EGF peptide is the most active species in all biological assays. A rapid method for purification of homogeneous complete EGF from commercial EGF preparations is described.     

Identification of hydropathically complementary putative contact sequences within epidermal growth factor (EGF) and the EGF receptor.

Hydropathic complementariness (HC) has been proposed as a novel molecular recognition code for how two proteins can recognize one other and thus form a reversible complex. If a protein contains a segment of a few amino acid residues that is surface-exposed, plus in extended conformation, plus composed of residues whose hydropathy pattern is opposite to that of a correspondingly sized segment on the respective other protein, this protein may bind to the other one through such a segment of HC (1). In order to identify in a pair of proteins sequences of HC we have developed the program PUTATIVE SITES SEARCHER (PSS-1) (2), a name that alludes to the possibility that such a segment of HC could represent a putative contact "site". Here we describe the application of PSS-1 to the study of human epidermal growth factor (EGF) and human EGF receptor (EGF-R). Six segments of HC were identified, two of which, designated a and b, fall exactly into experimentally verified contact regions on EGF as well as on EGF-R. Site a consists of residues 25.AEIYMCV.19 of EGF ("half site" aEGF) and of residues 331.NIKHFKN.337 of the EGF-R ("half site" aEGF-R); site b consists of residues 34.VCNCAY.29 of EGF and residues 365.PQELDI.370 of the EGF-R. Most interestingly, both half sites aEGF and bEGF localize in loop B of hEGF which is recognized as being essential for receptor binding. Similar is true for the half sites aEGF-R and bEGF-R that localize in subdomain III (residues 314-445) of the extracellular part of the EGF-R, also identified to be responsible for EGF binding. Thus, each of the two theoretically predicted sites is composed of half sites whose functional importance is experimentally verified. This correspondence supports the principal suitability of PSS-1 and suggests that EGF binds to EGF-R at least in part by means of HC contacts besides using, most probably, also "classical" (i.e. non-HC-type) contacts (e.g. charge interactions or hydrophobic bonds).     

The effect of the intersubunit disulfide bond on the structural and functional properties of the small heat shock protein Hsp25

The murine small heat shock protein Hsp25 carries a single cysteine residue in position 141 of its amino acid sequence. Interestingly, Hsp25 can exist within the cell as covalently bound dimer which is linked by an intermolecular disulfide bond between two monomers. Oxidative stress caused by treatment of the cells with diamide, arsenite, or hydrogen peroxide leads to an increase in Hsp25-dimerisation which can be blocked by simultaneous treatment with reducing agents. Recombinant Hsp25 was prepared in an oxidized dimeric (oxHsp25) and reduced monomeric (redHsp25) form. The two species were compared with regard to secondary structure, stability, oligomerization properties and their chaperone activity. It is demonstrated by CD measurements in the far UV region that there are no significant differences in the secondary structure and temperature- or pH-stability of oxHsp25 and redHsp25. However, according to CD measurements in the near UV region an increase in the asymmetry of the microenvironment of aromatic residues in oxHsp25 is observed. Furthermore, an increase in stability of the hydrophobic environment of the tryptophan residues mainly located in the N-terminal domain of the protein against urea denaturation is detected in oxHsp25. Both reduced and oxidized Hsp25 form oligomeric complexes of similar size and stability against detergents and both species prevent thermal aggregation of citrate synthase and assist significantly in oxaloacetic acid-induced refolding of the enzyme. Hence, the overall secondary structure, the degree of oligomerization and the chaperone activity of Hsp25 seem independent of the formation of the intermolecular disulfide bond and only the stability of the hydrophobic N-terminal part of the molecule is influenced by formation of this bound. The obtained data do not exclude the possible involvement of dimerization of this protein in other cellular functions, e.g. in intracellular sulfhydryl-buffering or in the protection of actin filaments from fragmentation upon oxidative stress.     

Rat epidermal growth factor: complete amino acid sequence. Homology with the corresponding murine and human proteins; isolation of a form truncated at both ends with full in vitro biological activity

Epidermal growth factor (EGF) isolated from the submaxillary gland of the rat (rEGF) is missing the COOH-terminal five residues present in both mouse and human EGF. rEGF competes for the binding of 125I-labelled mEGF to human carcinoma cells with the same affinity as mEGF. rEGF and mEGF have identical mitogenic activities on mouse 3T3 fibroblasts, thus the C-terminal region of the sequence is not necessary for the in vitro activity of EGF. Using reversed-phase high-performance liquid chromatography, four molecular forms of EGF have been extracted from rat submaxillary glands. These forms represent rEGF, rEGF(2-48), rEGF(3-48) and rEGF(4-48); all forms appear to be equipotent in both the receptor binding and mitogenic assays. The isoelectric points of these rEGFs are in the range of pH 5.1 to 5.2. The primary structure of rEGF was determined from approximately 10 micrograms protein by sequence analysis of the intact molecule and fragments obtained from the reduced and alkylated protein by chemical cleavage with CNBr and enzymic cleavage with chymotrypsin and a proline-specific endopeptidase. Subnanomole amounts of generated peptides were purified to homogeneity by reversed-phase microbore high-performance liquid chromatography and analysed by automated Edman degradation in a gas-phase sequencer. There are 48 amino acid residues in the complete polypeptide chain which lacks alanine, phenylalanine, lysine and tryptophan. The amino acid sequence of rat epidermal growth factor is: Asn-Ser-Asn-Thr-Gly-Cys-Pro-Pro-Ser-Tyr-Asp-Gly-Tyr-Cys-Leu-Asn- Gly-Gly-Val-Cys-Met-Tyr-Val-Glu-Ser-Val-Asp-Arg-Tyr-Val-Cys-Asn-Cys -Val-Ile-Gly-Tyr-Ile-Gly-Glu-Arg-Cys-Gln-His-Arg-Asp-Leu-Arg. The calculated relative molecular mass from the sequence analysis is 5377.     

The Hydroxyl Radical Generated by an Iron(II)/EDTA/Ascorbate System Preferentially Attacks Tryptophan Residues of the Protein

Iron(II)/EDTA/ascorbate-mediated oxidative damage to specific amino acid residues (tryptophan) of serum albumin was studied. The active species generated by Fe(II)/EDTA/ascorbate preferred to react with tryptophan residues rather than histidine or other amino acids. The observation of preferential damage to tryptophan residues of the protein was fully suported by a model experiment using a tryptophan analogue. The reaction of Fe(II)/EDTA/ascorbate to the protein was significantly suppressed by mannitol and dimethysulfoxide, suggesting the participation of the hydroxyl radical generated via Fenton’s reaction. The result was supported by the hydroxyl radical assay using 2-deoxyribose.     

Elephant prolactin: isolation and characterization

Prolactin was isolated from anterior lobes of elephant pituitary glands. It consisted of 199 amino acids with three disulfide bridges and two tryptophan residues as found in prolactin from other species. The sequence of the NH2-terminal 28 amino acids was determined and shown homologous with the ovine hormone. In comparison with ovine prolactin, a marked difference was seen in the methionine content; the elephant hormone possessed only 18-34% lactogenic potency. The conformation of elephant prolactin was examined by zero order, second order and circular dichroism spectroscopy. The alpha helical content was estimated to be about 60%. In comparison with prolactins from other species, the second order spectra of elephant prolactin suggest that the local microenvironment for one or both tryptophan residues is somewhat different.     

Purification and characterization of a low and a high molecular weight form of epidermal growth factor from rat urine

Two forms of epidermal growth factor (EGF) have been purified to homogeneity from rat urine by immunoaffinity chromatography and gel filtration. For one of the purified peptides the molecular mass has been determined to be 5891 by mass spectrometry. This peptide consists of 51 amino acid residues. The sequence of the first 48 amino acid residues is identical to the previously published sequence for submandibular rat EGF. The C-terminal three residues (49-51) are Trp-Trp-Lys. The other purified peptide has a molecular mass of 45 kDa as determined by SDS-polyacrylamide gel electrophoresis. The N-terminal sequence is Asn-Tyr-Lys-Asp-(Cys)-Gly-Pro-Gly-Gly-(Cys)-Gly-Ser-His-Ala. Both the high and the low molecular mass form of urinary rat EGF are able to bind to the human placenta receptor for EGF.     

Immunological detection of N-formylkynurenine in oxidized proteins

Reactions of tryptophan residues in proteins with radical and other oxidative species frequently lead to cleavage of the indole ring, modifying tryptophan residues into N-formylkynurenine (NFK) and kynurenine. Tryptophan modification has been detected in physiologically important proteins and has been associated with a number of human disease conditions. Modified residues have been identified through various combinations of proteomic analyses, tryptic digestion, HPLC, and mass spectrometry. Here we present a novel, immunological approach using polyclonal antiserum for detection of NFK. The specificity of our antiserum is confirmed using photooxidation and radical-mediated oxidation of proteins with and without tryptophan residues. The sensitivity of our antiserum is validated through detection of NFK in photooxidized myoglobin (two tryptophan residues) and in carbonate radical-oxidized human SOD1, which contains a single tryptophan residue. Analysis of photooxidized milk also shows that our antiserum can detect NFK residues in a mixture of proteins. Results from mass spectrometric analysis of photooxidized myoglobin samples corroborate the immunological data, detecting an increase in NFK content as the extent of photooxidation increases.     

Isolation and characterization of epidermal growth factor from human milk

Epidermal growth factor (EGF) has been purified from human milk. The purification was monitored with a human placental membrane radioreceptor assay using murine salivary epidermal growth factor I (mEGF I) as a competitive ligand and was achieved exclusively by the use of reverse-phase liquid chromatography (RPLC). The sequential use of preparative, semipreparative and analytical RPLC on an octylsilica support with solvent systems of different solute selectivity such as pyridine formate, triethylammonnium phosphate or perfluorocarbonic acids in the presence of n-propanol or acetonitrile allowed purification to homogeneity with 5 consecutive runs. The molecular mass, amino acid composition and NH2-terminal sequence of human EGF were determined. Gas-phase microsequencing of residues 1-17 revealed the following sequence: Asn-Ser-Asp-Ser-Glu-X-Pro-Leu-Ser-His-Asp-Gly-Tyr-X-Leu-X-Asp which is identical with the NH2-terminof urogastrone from human urine. The purified polypeptide competes with mEGF for the placental membrane receptor with a ki of 1 ng. Furthermore, it stimulates the anchorage-dependent as well as -independent proliferation of human and rat indicator cells with half-maximal stimulation at 1 and 2.5 ng/ml, respectively. Although human epidermal growth factor has been unequivocally identified in human milk and -for the first time-shown to be identical with urogastrone from human urine, the high-resolution techniques employed have also revealed the presence of EGF-related molecules which await further characterization. It is possible that EGF and the EGF-related growth factors possess important regulatory functions in normal growth of the human breast during pregnancy and lactation as well as in abnormal growth during mammary tumor formation and progression.     

Caffeine induces Ca2+ release by reducing the threshold for luminal Ca2+ activation of the ryanodine receptor

Myeloperoxidase, released by activated phagocytes, forms reactive oxidants by catalysing the reaction of halide and pseudo-halide ions with H(2)O(2). These oxidants have been linked to tissue damage in a range of inflammatory diseases. With physiological levels of halide and pseudo-halide ions, similar amounts of HOCl (hypochlorous acid) and HOSCN (hypothiocyanous acid) are produced by myeloperoxidase. Although the importance of HOSCN in initiating cellular damage via thiol oxidation is becoming increasingly recognized, there are limited data on the reactions of HOSCN with other targets. In the present study, the products of the reaction of HOSCN with proteins has been studied. With albumin, thiols are oxidized preferentially forming unstable sulfenyl thiocyanate derivatives, as evidenced by the reversible incorporation of (14)C from HOS(14)CN. On consumption of the HSA (human serum albumin) free thiol group, the formation of stable (14)C-containing products and oxidation of tryptophan residues are observed. Oxidation of tryptophan residues is observed on reaction of HOSCN with other proteins (including myoglobin, lysozyme and trypsin inhibitor), but not free tryptophan, or tryptophan-containing peptides. Peptide mass mapping studies with HOSCN-treated myoglobin, showed the addition of two oxygen atoms on either Trp(7) or Trp(14) with equimolar or less oxidant, and the addition of a further two oxygen atoms to the other tryptophan with higher oxidant concentrations (> or = 2-fold). Tryptophan oxidation was observed on treating myoglobin with HOSCN in the presence of glutathione and ascorbate. Thus tryptophan residues are likely to be favourable targets for the reaction in biological systems, and the oxidation products formed may be useful biomarkers of HOSCN-mediated protein oxidation.     

1H NMR assignment and secondary structure of the Ca2(+)-free form of the amino-terminal epidermal growth factor like domain in coagulation factor X

Blood coagulation factor X is composed of discrete domains, two of which are homologous to the epidermal growth factor (EGF). The N-terminal EGF like domain in factor X (fX-EGFN), residues 45-86 of the intact protein, contains a beta-hydroxylated aspartic acid and has one Ca2(+)-binding site. Using 2D NMR techniques, we have made a full assignment of the 500-MHz 1H NMR spectrum of Ca2(+)-free fX-EGFN. On the basis of this assignment and complementary NOESY experiments, we have also determined the secondary structure of Ca2(+)-free fX-EGFN in water solution. Residues 45-49 are comparatively mobile, whereas residues 50-56 are constrained by two disulfide bonds to one side of an antiparallel beta-sheet involving residues 59-64 and 67-72. Another antiparallel beta-sheet involves residues 76-77 and 83-84. A small, parallel beta-sheet connects residues 80-81 and 55-56 and thereby orients the two antiparallel beta-sheets relative to each other. Four beta-turns are identified, involving residues 50-53, 56-59, 64-67, and 73-76. Residues 78-82 adopt an extended bend structure. On the basis of secondary structure and the location of the three disulfide bonds, we find that Asp 46, Asp 48, and Hya 63 are sufficiently close to each other to form a Ca2(+)-binding site. However, the amino terminus of the Ca2(+)-free form of fX-EGFN is not part of a triple-stranded beta-sheet as in other EGF like peptides. Differences and similarities between fX-EFGN and murine EGF with respect to secondary structure and conformational shifts are discussed.     

Expressed murine and human CDR-H3 intervals of equal length exhibit distinct repertoires that differ in their amino acid composition and predicted range of structures

Immunoglobulin junctional diversity is concentrated in the third complementarity-determining region of the heavy chain (CDR-H3), which often plays a dominant role in antigen binding. The range of CDR-H3 lengths in mouse is shorter than in human, and thus the murine repertoire could be presumed to be a subset of the human one. To test this presumption, we analyzed 4751 human and 2170 murine unique, functional, published CDR-H3 intervals. Although tyrosine, glycine, and serine were found to predominate in both species, the human sequences contained fewer tyrosine residues, more proline residues, and more hydrophobic residues (p<0.001, respectively). While changes in amino acid utilization as a function of CDR-H3 length followed similar trends in both species, murine and human CDR-H3 intervals of identical length were found to differ from each other. These differences reflect both divergence of germline diversity and joining gene sequence and somatic selection. Together, these factors promote the production of a rather uniform repertoire in mice of tyrosine-enriched CDR-H3 loops with stabilized hydrogen bond-ladders versus a much more diverse repertoire in human that contains CDR-H3 loops sculpted by the presence of intra-chain disulfide bonds due to germline-encoded cysteine residues as well as the enhanced presence of somatically generated proline residues that preclude hydrogen bond ladder formation. Thus, despite the presumed need to recognize a similar range of antigen epitopes, the murine CDR-H3 repertoire is clearly distinct from its human counterpart in its amino acid composition and its predicted range of structures. These findings represent a benchmark to which CDR-H3 repertoires can be compared to better characterize and understand the shaping of the CDR-H3 repertoire over evolution and during immune responses. This information may also be useful for the design of species-specific CDR-H3 sequences in synthetic antibody libraries.     

Cloning and expression of ovine placental lactogen

Ovine placental lactogen (oPL) is active in a wide range of GH and PRL assays, a property that it shares with human GH (hGH). In addition, oPL is one of a small number of hormones that bind the human GH receptor with high affinity. In order to compare the sequence of oPL to the sequences of other members of the GH family, full-length cDNA clones have been isolated. These clones predict that the full sequence of oPL contains 198 amino acids preceded by a 38 amino acid signal sequence. The mature oPL sequence includes six cysteine and two tryptophan residues and shows substantially more identity to bovine PL (67%) and oPL (49%) than to mouse (31%) or human (25%) PL or to oGH (28%) or (26%) hGH. Like the natural hormone, oPL expressed in mammalian tissue cells binds with high affinity to a soluble form of the recombinant hGH receptor. Thus, oPL binds to the human receptor in spite of having a sequence that is considerably divergent from hGH. Interestingly, the sequence of oPL differs from hGH at most of the amino acids recently found by mutagenesis studies to be important residues in the binding of hGH to the human receptor.     

Epidermal growth factor receptor threonine and serine residues phosphorylated in vivo

The epidermal growth factor (EGF) receptor is regulated by EGF-stimulated autophosphorylation and by phorbol ester-stimulated, protein kinase C (Ca2+/phospholipid-dependent enzyme) mediated phosphorylation at identified sites. The EGF receptor contains additional phosphorylation sites including a prominent phosphothreonine and several phosphoserines which account for the majority of phosphate covalently bound to the receptor in vivo. We have identified three of these sites in EGF receptor purified from 32P-labeled A431 cells. The major phosphothreonine was identified as threonine 669 in the EGF receptor sequence. Phosphoserine residues were identified as serines 671 and 1046/1047 of the EGF receptor. Two other phosphoserine residues were localized to tryptic peptides containing multiple serine residues located carboxyl-terminal to the conserved protein kinase domain. The amino acid sequences surrounding the three identified phosphorylation sites are highly conserved in the EGF receptor and the protein products of the v-erb B and neu oncogenes. Analysis of predicted secondary structure of the EGF receptor reveals that all of the phosphorylation sites are located near beta turns. In A431 cells phosphorylation of the serine residues was dependent upon serum. In mouse B82 L cells transfected with a wild type human EGF receptor. EGF increased the 32P content in all tryptic phosphopeptides. A mutant EGF receptor lacking protein tyrosine kinase activity was phosphorylated only at threonine 669. Regulated phosphorylation of the EGF receptor at these threonine and serine residues may influence aspects of receptor function.     

Localization of epidermal growth factor precursor in tooth and lung during embryonic mouse development

The murine epidermal growth factor (EGF) precursor is a 1217 amino acid protein which contains mature EGF (amino acid residues 977-1029) as well as eight EGF-like repeats. Although the highest levels of EGF are found in the adult male mouse submandibular gland, the results of in situ hybridization studies and mRNA analyses suggest that EGF precursor mRNA is synthesized in several adult mouse tissues including the lung and the incisor. To determine if EGF precursor gene expression is intrinsic to the developmental program for either embryonic tooth or lung organogenesis, sense and antisense oligodeoxyribonucleotide probes corresponding to amino acids 1070-1081 of the precursor were used to localize cellular sites of synthesis of EGF precursor mRNA by in situ hybridization. Antibodies directed against amino acid residues 348-691 of the precursor were used in immunodetection techniques to identify either EGF precursor protein or processed derivatives. In contrast to earlier reports indicating that embryonic mouse tissues do not synthesize EGF precursor mRNA, we found that EGF precursor mRNA is present in clusters of ectoderm-, mesoderm-, and ectomesenchyme-derived cells associated with embryonic teeth and lung organs. Moreover, epitopes common to the EGF precursor were immunolocalized in both the epithelial and mesenchymal tissues of embryonic mouse tooth and lung organs. These results suggest that the EGF precursor and/or motifs contained within the precursor molecule, including mature EGF, may play an instructive or permissive role in epithelial-mesenchymal interactions pursuant to organogenesis.