Ror2, encoding a receptor-like tyrosine kinase, is required for cartilage and growth plate development.

Receptor tyrosine kinases often have critical roles in particular cell lineages by initiating signalling cascades in those lineages. Examples include the neural-specific TRK receptors, the VEGF and angiopoietin endothelial-specific receptors, and the muscle-specific MUSK receptor. Many lineage-restricted receptor tyrosine kinases were initially identified as 'orphans' homologous to known receptors, and only subsequently used to identify their unknown growth factors. Some receptor-tyrosine-kinase-like orphans still lack identified ligands as well as biological roles. Here we characterize one such orphan, encoded by Ror2 (ref. 12). We report that disruption of mouse Ror2 leads to profound skeletal abnormalities, with essentially all endochondrally derived bones foreshortened or misshapen, albeit to differing degrees. Further, we find that Ror2 is selectively expressed in the chondrocytes of all developing cartilage anlagen, where it essential during initial growth and patterning, as well as subsequently in the proliferating chondrocytes of mature growth plates, where it is required for normal expansion. Thus, Ror2 encodes a receptor-like tyrosine kinase that is selectively expressed in, and particularly important for, the chondrocyte lineage.

Genomic organization and chromosomal localization of the human and mouse genes encoding the alpha receptor component for ciliary neurotrophic factor.

Ciliary neurotrophic factor (CNTF) has recently been found to share receptor components with, and to be structurally related to, a family of broadly acting cytokines, including interleukin-6, leukemia inhibitory factor, and oncostatin M. However, the CNTF receptor complex also includes a CNTF-specific component known as CNTF receptor alpha (CNTFR alpha). Here we describe the molecular cloning of the human and mouse genes encoding CNTFR. We report that the human and mouse genes have an identical intron-exon structure that correlates well with the domain structure of CNTFR alpha. That is, the signal peptide and the immunoglobulin-like domain are each encoded by single exons, the cytokine receptor-like domain is distributed among 4 exons, and the C-terminal glycosyl phosphatidylinositol recognition domain is encoded by the final coding exon. The position of the introns within the cytokine receptor-like domain corresponds to those found in other members of the cytokine receptor superfamily. Confirming a recent study using radiation hybrids, we have also mapped the human CNTFR gene to chromosome band 9p13 and the mouse gene to a syntenic region of chromosome 4.

A novel family of cell surface receptors with tyrosine kinase-like domain.

Human cDNA clones encoding two novel proteins with a region strongly homologous to the tyrosine kinase domain of growth factor receptors, in particular of the Trk family, were obtained by a polymerase chain reaction-based approach. These proteins, Ror1 and Ror2, share 58% overall amino acid identity and a structure indicative of cell surface molecules. A secretion signal sequence and a transmembrane domain delimit the extracellular portion, which contains immunoglobulin-like, cysteine-rich, and kringle domains. The cytoplasmic portion contains the tyrosine kinase-like domain which (in Ror2) appears to be associated with protein kinase activity in vitro, followed by serine/threonine- and proline-rich motifs. Partial nucleotide sequences of the rat genes reveal striking evolutionary conservation of the proteins between human and rat. The level of expression of the rat genes is high in the head and body of early embryo and decreases dramatically after embryonic day 16. Based on these data, Ror1 and Ror2 appear to define a new developmentally regulated family of cell surface receptors for unidentified ligands.

Recombinant human and rat ciliary neurotrophic factors.

The human ciliary neurotrophic factor (CNTF) gene was identified and cloned, based on homology with the recently cloned rat cDNA. The gene encodes a protein of 200 amino acids, which shares about 80% sequence identity with rat and rabbit CNTF and, like these homologues, lacks an apparent secretion signal sequence. The human CNTF gene, like the rat gene, appears to contain a single intron separating two protein coding exons. An intronless human CNTF gene was constructed by the use of polymerase chain reactions and introduced into vectors designed for expression of foreign proteins in E. coli. The rat CNTF gene was also introduced into similar vectors. Both the human and rat proteins were expressed at exceptionally high levels, at 20-40% and 60-70% of total protein, respectively. Extraction of the recombinant proteins from inclusion bodies by guanidinium chloride, followed by two column chromatography steps, produced high yields of pure CNTF that supported survival and neurite outgrowth from embryonic chick ciliary neurons in culture. The biological activity of both recombinant proteins was comparable to that of native rat CNTF.

trkB encodes a functional receptor for brain-derived neurotrophic factor and neurotrophin-3 but not nerve growth factor.

A variety of findings seem to functionally link brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3), while distinguishing both of these factors from the third member of the neurotrophin family, nerve growth factor (NGF). Here we demonstrate that all three of these neuronal survival molecules bind similarly to the low affinity NGF receptor, but that BDNF and NT-3, unlike NGF, do not act via the high affinity NGF receptor. However, both BDNF and NT-3, but not NGF, bind to full-length and truncated forms of a receptor-like tyrosine kinase, trkB, for which no ligand had previously been identified. In addition to binding BDNF and NT-3, trkB can mediate functional responses to both of these neurotrophins when it is expressed in PC12 cells, although BDNF appears to be the more effective ligand. Thus trkB encodes an essential component of a functional receptor for BDNF and NT-3, but not for NGF. Further evidence predicts the existence of additional functional receptors for the neurotrophins.

Changes in PC12 cell morphology induced by transfection with 42C cDNA, coding for a member of the S-100 protein family.

The cloned DNA coding for 42C protein (light chain of calpactin I), whose mRNA is induced in PC12 cells by treatment with nerve growth factor (NGF), was reintroduced into these cells. A cell line was obtained in which the outgrowth of processes in the absence of added NGF, similar to that induced in the parental PC12 cells by the factor, was accompanied by high levels of 42C RNA. The apparent reason for this constitutive overexpression of 42C is the stable integration of multiple copies of the 42C DNA into the cell genome. These results further support the notion that S-100 protein family, of which 42C is a member, may play an important role in development.

Molecular cloning, expression and regional distribution of rat ciliary neurotrophic factor.

Ciliary neurotrophic factor (CNTF) was originally characterized as a survival factor for chick ciliary neurons in vitro. More recently, it was shown to promote the survival of a variety of other neuronal cell types and to affect the differentiation of E7 chick sympathetic neurons by inhibiting their proliferation and by inducing the expression of vasoactive intestinal peptide immunoreactivity (VIP-IR). In cultures of dissociated sympathetic neurons from newborn rats, CNTF induces cholinergic differentiation as shown by increased levels of choline acetyltransferase (ChAT). This increase is paralleled by a reduction of tyrosine hydroxylase (TH) activity. Moreover, CNTF promotes the differentiation of bipotential 02A progenitor cells to type-2-astrocytes in vitro. To help establish which, if any, of these functions CNTF exerts in vivo, it is necessary to determine its primary structure, cellular expression, developmental regulation and localization. The complementary DNA-deduced amino-acid sequence and subsequent expression of cDNA clones covering the entire coding region in HeLa-cells indicate that CNTF is a cytosolic protein. This, together with its regional distribution and its developmental expression, show that CNTF is not a target-derived neurotrophic factor. CNTF thus seems to exhibit neurotrophic and differentiation properties only after becoming available either by cellular lesion or by an unknown release mechanism.

Molecular cloning and expression of brain-derived neurotrophic factor.

During the development of the vertebrate nervous system, many neurons depend for survival on interactions with their target cells. Specific proteins are thought to be released by the target cells and to play an essential role in these interactions. So far, only one such protein, nerve growth factor, has been fully characterized. This has been possible because of the extraordinarily (and unexplained) large quantities of this protein in some adult tissues that are of no relevance to the developing nervous system. Whereas the dependency of many neurons on their target cells for normal development, and the restricted neuronal specificity of nerve growth factor have long suggested the existence of other such proteins, their low abundance has rendered their characterization difficult. Here we report the full primary structure of brain-derived neurotrophic factor. This very rare protein is known to promote the survival of neuronal populations that are all located either in the central nervous system or directly connected with it. The messenger RNA for brain-derived neurotrophic factor was found predominantly in the central nervous system, and the sequence of the protein indicates that it is structurally related to nerve growth factor. These results establish that these two neurotrophic factors are related both functionally and structurally.

Nerve growth factor induces the genes for two proteins related to a family of calcium-binding proteins in PC12 cells.

Differential hybridization of a cDNA library from rat pheochromocytoma PC12 cells with cDNA probes from naive PC12 cells and from PC12 cells exposed to nerve growth factor for 7 days identified cDNA sequences of two genes induced by NGF. The mRNA species detected by these cDNA sequences, designated 42A and 42C, reached maximal levels after 24 hr of treatment with NGF and were still significantly higher than control levels after 7 days. Epidermal growth factor transiently induced both mRNAs but at much lower levels. The mRNAs code for 95- (42C) and 101- (42A) amino acid residue peptides whose sequences are homologous to those of a family of calcium-binding proteins including the S-100 protein. The conservation of primary and secondary structure between 42A, 42C, and the other proteins suggests a possible role for them in the regulation of cell growth and differentiation.

Sequence of the pS2 mRNA induced by estrogen in the human breast cancer cell line MCF-7.

We present the complete sequence of an mRNA which is induced by estrogen in the human breast cancer cell line MCF-7 [pS2 mRNA, Masiakowski et al., Nucleic Acids Res. 10, 7895-7903 (1982)]. Primer extension and cloning of double-stranded cDNA (ds-cDNA) into a vector designed to make full-length cDNA were used to determine the sequence of the fifteen 5'-terminal nucleotides which were not present in the original pS2 ds-cDNA clone. The mRNA sequence has a major open reading frame encoding 84 amino-acids, flanked by a 40 nucleotide 5'-untranslated region and a 198 nucleotide 3'-untranslated region preceding the polyA tail. The 3'-untranslated region contains a polyadenylation signal, AUUAAA, 14 nucleotides upstream from the polyA tail. The derived protein sequence contains a putative signal peptide region suggesting that the protein may be secreted. The nucleotide and derived amino-acid sequences were compared to previously determined sequences, particularly to those of hormone-regulated proteins and growth factors, and no obvious similarities were observed.

Cloning of cDNA sequences of hormone-regulated genes from the MCF-7 human breast cancer cell line.

cDNA clones corresponding to a mRNA whose level is rapidly increased by addition of oestradiol to the culture medium have been isolated by differential screening of a cDNA library from the breast cancer cell line MCF-7, which contains oestrogen receptors. Such clones will be useful in studies of the DNA sequences required for hormonal induction and to determine whether expression of the corresponding gene is in any way related to the cancerous state. We have also obtained a cDNA clone for a messenger whose level is apparently decreased by steroid hormones.

Dissection of the active site of rabbit liver tRNA nucleotidyltransferase. Specificity and properties of the tRNA and acceptor subsites determined with model acceptor substrates.

The specificity of rabbit liver tRNA nucleotidyltransferase with respect to its interaction with acceptor residues at the 3' end of tRNA was analyzed using a model acceptor system consisting of dinucleoside monophosphates or nucleosides. Of all the dinucleoside monophosphates tested, only CpC was an active AMP acceptor, indicating that the specificity of the enzyme conforms exactly to the structure present at the 3' terminus of the natural acceptor, tRNA-C-C. Similarly, CMP incorporation into model acceptors closely paralleled the specificity seen with tRNA-C and tRNA-X. Competition studies between the model acceptors and tRNAs with modified 3' termini suggested that the model compounds bind to the enzyme at the site normally recognizing the 3' terminus of tRNA. Comparison of nucleotide incorporation into tRNAs and into the model acceptors revealed a number of differences which allowed us to separate effects on tRNA structure from direct effects on the reaction. These studies enabled us to distinguish several subsites on the enzyme: an ATP-donor site, two sites specifically recognizing the 2 terminal C residues on tRNA, and a site recognizing the nonreacting part of the tRNA. Thus, these results support several features of the multisite model previously proposed (Deutscher, M. P. (1972) J. Biol. Chem. 247, 459-468) to explain tRNA nucleotidyltransferase action.

Dissection of the active site of rabbit liver tRNA nucleotidyltransferase. Specificity and properties of subsites for donor nucleotide triphosphates.

tRNA nucleotidyltransferase incorporates both AMP and CMP into tRNA acceptors. Studies of the effects of nucleoside triphosphates, nucleotide analogues, and affinity reagents on AMP and CMP incorporation indicate that these residues are donated from different subsites. However, neither of these sites is completely specific for nucleoside triphosphate binding, and CMP can actually be incorporated from the AMP-donating site, although at a slow rate. The two donor subsites interact with each other, such that binding of a ligand to the ATP site stimulates incorporation from the CMP-donating site. This interaction accounts for the biphasic CTP saturation curve and the unusual effects of nucleoside triphosphates on CMP incorporation observed earlier. In addition to donating CMP, the CTP subsite also serves as the position of binding of the terminal C residue of tRNA-C-C and, in the absence of CTP, for binding of the terminal residue of tRNA-C. These results, together with those in the accompanying paper, have defined multiple accepting and donating subsites within the active site of tRNA nucleotidyltransferase, as predicted from our previous model for enzyme action (Deutscher, M. P. (1972) J. Biol. Chem. 247, 459-468). However, since we have been unable to obtain definitive evidence for two CMP-donating sites, we have considered a modification of this earlier model which utilizes only a single CMP-donating site. Using these models, we discuss how the specificity of the donor and acceptor subsites ensures the accurate synthesis of the -C-C-A sequence of tRNA.

Separation of functionally distinct regions of a macromolecular substrate. Stimulation of tRNA nucleotidyltransferase by a nonreacting fragment of tRNA.

Rabbit liver tRNA nucleotidyltransferase catalyzes the incorporation of AMP and CMP into the model acceptor substrate, cytidine. The apparent Km for cytidine in this reaction is about 80 to 90 mM which is more than 10(4) greater than the Km values for the natural substrates, tRNA lacking the terminal AMP (tRNA-C-C) and tRNA lacking the terminal pCpA (tRNA-C). The Vmax values for the model reaction are only 5% and 2% of those for the reaction with the natural tRNA substrates. Addition of the tRNA fragments, tRNA lacking the terminal XpCpCpA sequence (tRNA-(X - 1)p) and tRNA lacking the terminal CpCpA (tRNA-Xp), greatly stimulates the rate of nucleotide incorporation into cytidine. In the case of CMP incorporation into cytidine, tRNA-Xp stimulates the reaction about 60-fold, to a rate similar to that of the normal reaction with tRNA-C. The tRNA fragment has no effect on the apparent Km of either cytidine or CTP, but only alters the Vmax of the reaction. Stimulation of the model reactions is maximal with tRNA fragments of specific chain lengths. These results provide direct evidence that the nonreacting regions of a substrate molecule play an important role in the catalytic efficiency of an enzyme.

Binding of tRNA nucleotidyltransferase to Affi-Gel Blue: rapid purification of the enzyme and binding studies.

Rabbit liver tRNA nucleotidyldransferase bound to columns of Affi-Gel Blue and could be specifically eluted with tRNA. This observation led to development of a rapid purification procedure for the enzyme. The adsorbent was also used to assess interaction of tRNA nucleotidyltransferase with various polynucleotides and substrates. The enzyme could be efficiently desorbed from Affi-Gel Blue by low concentrations of tRNA-C-C, less well by tRNA-C-C-A, and not at all by poly(A), poly(C), ATP or CTP.

A kinetic study of the pH-dependent properties of the ferric undecapeptide of cytochrome c (microperoxidase).

The ferric form of the haem undecapeptide, derived from horse cytochrome c by peptic digestion, undergoes at least three pH-induced transitions with pK values of 3.4, 5.8 and 7.6. Temperature-jump experiments suggest that the first of these is due to the binding of a deprotonated imidazole group to the feric iron while the second and third arise from the binding of the two available amino groups present (the alpha-NH2 of valine and the epsilon-NH2 of lysine). Molecular models indicate that steric retraints on the peptide dictate that these amino groups may only coordinate to iron atoms via intermolecular bonds, thus leading to the polymerization of the peptide. Cyanide binding studies are in agreement with these conclusions and also yield a value of 3.6 X 10(6) M-1 s-1 for the intrinsic combination constant of CN- anion with the haem. A model is proposed which describes the pH-dependent properties of the ferric undecapeptide.