Structural analysis of the regulatory elements of the type-II procollagen gene. Conservation of promoter and first intron sequences between human and mouse

A missense mutation in the mouse Col2a1 gene causes spondyloepiphyseal dysplasia congenita, hearing loss, and retinoschisis

A missense mutation in the mouse Col2a1 gene has been discovered, resulting in a mouse phenotype with similarities to human spondyloepiphyseal dysplasia (SED) congenita. In addition, SED patients have been identified with a similar molecular mutation in human COL2A1. This mouse model offers a useful tool for molecular and biological studies of bone development and pathology.

INTRODUCTION

A new mouse autosomal recessive mutation has been discovered and named spondyloepiphyseal dysplasia congenita (gene symbol sedc).

MATERIALS AND METHODS

Homozygous sedc mice can be identified at birth by their small size and shortened trunk. Adults have shortened noses, dysplastic vertebrae, femora, and tibias, plus retinoschisis and hearing loss. The mutation was mapped to Chr15, and Col2a1 was identified as a candidate gene.

RESULTS

Sequence analyses revealed that the affected gene is Col2a1, which has a missense mutation at exon 48 causing an amino acid change of arginine to cysteine at position 1417. Two human patients with spondyloepiphyseal dysplasia (SED) congenita have been reported with the same amino acid substitution at position 789 in the human COL2A1 gene.

CONCLUSIONS

Thus, sedc/sedc mice provide a valuable model of human SED congenita with molecular and phenotypic homology. Further biochemical analyses, molecular modeling, and cell culture studies using sedc/sedc mice could provide insight into mechanisms of skeletal development dependent on Col2a1 and its role in fibril formation and cartilage template organization.

Egr-1 mediates transcriptional repression of COL2A1 promoter activity by interleukin-1beta

Following induction and activation of the early growth response (Egr)-1 transcription factor in human chondrocytes, interleukin-1beta (IL-1beta) suppresses the expression of the type II collagen gene (COL2A1), associated with induction of Egr-1 binding activity in nuclear extracts. The COL2A1 proximal promoter contains overlapping binding sites for Egr-1 and Sp1 family members at -119/-112 bp and -81/-74 bp. Mutations that block binding of Sp1 and Sp3 to either site markedly reduce constitutive expression of the core promoter. IL-1beta-induced Egr-1 binds strongly to the -119/-112 bp site, and mutations that block Egr-1 binding prevent inhibition by IL-1beta. Cotransfection with pCMV-Egr1 potentiates the inhibition of COL2A1 promoter activity by IL-1beta, whereas overexpression of dominant-negative Egr-1 mutant, Wilm's tumor-1 (WT1)/Egr1, Sp1, or Sp3 reverses the inhibition by IL-1beta. Cotransfection of pGL2-COL2/Gal4, in which we substituted the critical residue for Egr-1 binding with a Gal4 binding domain and a pCMV-Gal4-Egr1 chimera permits an inhibitory response to IL-1beta that is reversed by overexpression of Gal4-CBP. Our results indicate that IL-1beta-induced activation of Egr-1 binding is required for inhibition of COL2A1 proximal promoter activity and suggest that Egr-1 acts as a repressor of a constitutively expressed collagen gene by preventing interactions between Sp1 and the general transcriptional machinery.

The TATA-containing core promoter of the type II collagen gene (COL2A1) is the target of interferon-gamma-mediated inhibition in human chondrocytes: requirement for Stat1 alpha, Jak1 and Jak2

Interferon-gamma (IFN-gamma) inhibits the synthesis of the cartilage-specific extracellular matrix protein type II collagen, and suppresses the expression of the type II collagen gene ( COL2A1 ) at the transcriptional level. To further examine this mechanism, the responses of COL2A1 regulatory sequences to IFN-gamma and the role of components of the Janus kinase/signal transducer and activators of transcription (JAK/STAT) pathway were examined in the immortalized human chondrocyte cell line, C-28/I2. IFN-gamma inhibited the mRNA levels of COL2A1 and aggrecan, but not Sox9, L-Sox5 and Sox6, all of which were expressed by these cells as markers of the differentiated phenotype. IFN-gamma suppressed the expression of luciferase reporter constructs containing sequences of the COL2A1 promoter spanning -6368 to +125 bp in the absence and presence of the intronic enhancer and stimulated activity of the gamma-interferon-activated site (GAS) luciferase reporter vector, associated with induction of Stat1 alpha-binding activity in nuclear extracts. These responses to IFN-gamma were blocked by overexpression of the JAK inhibitor, JAK-binding protein (JAB), or reversed by dominant-negative Stat1 alpha Y701F containing a mutation at Tyr-701, the JAK phosphorylation site. IFN-gamma had no effect on COL2A1 promoter expression in Jak1 (U4A)-, Jak2 (gamma 2A)- and Stat1 alpha (U3A)-deficient cell lines. In the U3A cell line, the response to IFN-gamma was rescued by overexpression of Stat1 alpha, but not by either Stat1 alpha Y701F or Stat1 beta. Functional analysis using deletion constructs showed that the IFN-gamma response was retained in the COL2A1 core promoter region spanning -45 to +11 bp, containing the TATA-box and GC-rich sequences but no Stat1-binding elements. Inhibition of COL2A1 promoter activity by IFN-gamma persisted in the presence of multiple deletions within the -45/+11 bp region. Our results indicate that repression of COL2A1 gene transcription by IFN-gamma requires Jak1, Jak2 and Stat1 alpha and suggest that this response involves indirect interaction of activated Stat1 alpha with the general transcriptional machinery that drives constitutive COL2A1 expression.

Diagnostic features and pedodontic-orthodontic management in dentinogenesis imperfecta type II: a case report

Dentinogenesis imperfecta type II, also known as hereditary opalescent dentin, is an isolated inherited condition transmitted as an autosomal dominant trait affecting the primary and permanent dentition. The combined pedodontic-orthodontic management of a 4-year-old child is described. Following orthodontic analysis to encourage a favourable growth outcome, treatment comprised restoration of the primary teeth with stainless steel crowns and composite crowns. Differential diagnosis and alternative therapies, including orthodontic considerations, are discussed.

Molecular cloning, sequencing, and tissue and developmental expression of mouse cartilage oligomeric matrix protein (COMP)

Mouse cartilage oligomeric matrix protein cDNA was cloned and sequenced by a reverse transcription-polymerase chain reaction. The open reading frame encoded a product of 755 amino acids that shares a high degree of identity to and possesses all the characteristic molecular features of both rat and human cartilage oligomeric matrix protein. This suggests that cartilage oligomeric matrix protein is highly conserved during evolution. The clone was 83, 84, and 95% identical to human, bovine, and rat cartilage oligomeric matrix protein cDNA, respectively. In tissues from the adult mouse, cartilage oligomeric matrix protein was expressed not only in cartilage and tendon but in trachea, bone, skeletal muscle, eye, heart, and placenta as well, and no expression was found in other tissues. Immunohistology revealed that cartilage oligomeric matrix was deposited as early as 10 days post coitus in predifferentiated mouse embryo mesenchyme. It was detected in all cartilaginous tissues and in the skeletal muscles of the embryo at day 13. As development progressed, accumulation of cartilage oligomeric matrix protein was marked in the growth plate. At 19 days post coitus, it was prominently deposited in the hypertrophic zone of the growth plate, perichondrium, and periosteum and in the superficial layer of the articular cartilage surface but was absent in the more central areas of the epiphyseal cartilage. The restricted tissue distribution and expression of cartilage oligomeric matrix protein in developing as well as adult mouse tissues suggest the regulation of this protein at the transcriptional level. The findings reported herein are the first detailed characterization of the distribution of cartilage oligomeric matrix protein during early skeletal development of the mouse.

Col2-GFP reporter marks chondrocyte lineage and chondrogenesis during mouse skeletal development

Mice were generated in which a Col2-GFP transgene serves as a reporter for the chondrocyte lineage and for chondrogenesis in live embryos and newborn pups. Cells actively engaged in chondrogenesis were identified by confocal optical sectioning within their native environments in embryos and in thick tissue slices. Chondrocytes exhibiting GFP fluorescence were purified from rib cages by high-speed cell sorting of crude cell suspensions. Intensity of fluorescence correlated with biosynthesis of procollagen II in these cells. The use of these mice and their cells provides a novel approach for studying chondrocyte differentiation and chondrogenesis during skeletal development.

Interaction of Ap1, Ap2, and Sp1 with the regulatory regions of the human pro-alpha1(I) collagen gene

In the pro-alpha1(I) collagen gene a number of cis-regulatory elements, which interact with a variety of trans-acting factors, are present in the promoter and first intron. We have undertaken a comprehensive study of Sp1, Ap1, and Ap2 binding in the region spanning -442 to +1697 nt. DNase I footprinting analysis revealed these factors bind with varying affinities to some of the potential sites: Sp1 binds to 16 of 34 potential sites, Ap2 binds to 22 of 40 potential binding sites, and Ap1 binds to its only potential site. The Sp1 sites were mostly clustered in the intron region, while the Ap2 sites were clustered in the promoter region. Transmission electron microscopic analysis of DNA-protein complexes not only confirmed these results, but also clearly showed that heterologous and/or homologous protein-protein interactions between Sp1 and/or Ap2 bring the promoter and intron in contact with each other, with the resulting looping out of the intervening DNA. This strongly suggests that the DNA-looping model is an explanation for the orientation preference of the enhancing element in the first intron as these interactions possibly create an optimum environment for the binding of the rest of the transcriptional machinery.

The non-collagenous dentin matrix proteins are involved in dentinogenesis imperfecta type II (DGI-II)

Dentinogenesis Imperfecta type II (DGI-II) is a localized form of mesodermal dysplasia of the dentin affecting both the primary and permanent dentitions. This is an autosomal-dominant disease in which there is a disorder in dentin mineralization. Several studies have localized DGI-II to human chromosome 4 in the region 4q 12-21. Many ECM genes-such as OPN, DMP1, DMP2, DMP3 (DSPP), and BSP-have been mapped to the same locus. Biochemical studies indicated that dentin phosphophoryn (DMP2) might be a candidate gene in DGI-II. In this study, we have used histological and RFLP analyses of tissues from a DGI-II-affected patient, as compared with two normal controls, to determine if DMP1, 2, or 3 was linked to DGI-II. The histology of the affected tooth was very different in the DGI-II patient as compared with the normals. In particular, the dentinal tubules in the DGI-II patient were very irregular, which could be the result of perturbations in the process of dentin formation. Patient and control DNA samples were digested with EcoRI or PstI and Southern-hybridized with the DMP1, DMP2, and DMP3 cDNAs. Few differences in the restriction pattern were observed between affected and normal samples for DMP1 and DMP3-3' region (phosphophoryn-like sequences) probes. On the other hand, DMP2 showed a dramatic shift in the restriction pattern in DGI-II. This study suggests that the different restriction enzyme digestion profiles of the DNA from the DGI-II patient, as probed by DMP2, might be related to the defective mineralization of dentin in DGI-II.

SV40 large T antigen expression driven by col2a1 regulatory sequences immortalizes articular chondrocytes but does not allow stabilization of type II collagen expression

Immortalization of chondrocytes by SV40 T Ag has often been reported to trigger the loss of expression of type II collagen, one of the main differentiation markers, although some immortalized chondrocyte lines maintaining a differentiated phenotype have also been described. Here, we show using transient cotransfections in differentiated chondrocytes that, in contrast to c-src, neither SV40 T Ag, nor c-myc, decreases col2a1 transcriptional activity. Then, we report the possibility of immortalizing rabbit articular chondrocytes by expression of SV40 T Ag controlled by the col2a1 promoter and enhancer (pCol2SV). This strategy allows one to select within a population of differentiated chondrocytes those which are able to maintain functional regulation of the col2a1 gene through long-term culture. In precrisis pCol2SV-transfected chondrocytes, all-trans-retinoic acid, a down-regulator of col2a1 expression, induced apoptosis, strongly suggesting the strict control of T Ag expression by col2a1 regulatory sequences. Some pCol2SV-transfected chondrocytes were definitively immortalized, after a short crisis period. However, type II collagen synthesis was restricted to a small proportion of cells, which went on to decrease with subculture, while the proportion of cells expressing T Ag was not affected. In these postcrisis cells, T Ag remained at least partially under the control of functional col2a1 regulatory elements as assessed by all-trans-retinoic acid down-regulation.

Human COL9A1 and COL9A2 genes. Two genes of 90 and 15 kb code for similar polypeptides of the same collagen molecule

Here we report the complete structure for the human COL9A1 and the complete sequence for the human COL9A2 genes. The COL9A1 gene is about 90 kb and consists of 38 exons. The COL9A2 gene is only about 15 kb, and it contains 32 exons. Sequence analysis of the promoter regions for the human COL9A2, the mouse Col9a2 and the human COL2A1 genes identified a conserved 14 bp sequence. The data also indicated that the alternative exon 1* found in intron 6 of the COL9A1 gene is separated from exon 7 only by a short intron in the chick, human, mouse and rat genes probably explaining why transcripts from exon 1* are spliced directly to exon 8.

Different cis-regulatory DNA elements mediate developmental stage- and tissue-specific expression of the human COL2A1 gene in transgenic mice

Expression of the type II collagen gene (human COL2A1, mouse Col2a1) heralds the differentiation of chondrocytes. It is also expressed in progenitor cells of some nonchondrogenic tissues during embryogenesis. DNA sequences in the 5' flanking region and intron 1 are known to control tissue-specific expression in vitro, but the regulation of COL2A1 expression in vivo is not clearly understood. We have tested the regulatory activity of DNA sequences from COL2A1 on the expression of a lacZ reporter gene in transgenic mice. We have found that type II collagen characteristic expression of the transgene requires the enhancer activity of a 309-bp fragment (+2, 388 to +2,696) in intron 1 in conjunction with 6.1-kb 5' sequences. Different regulatory elements were found in the 1.6-kb region (+701 to +2,387) of intron 1 which only needs 90-bp 5' sequences for tissue-specific expression in different components of the developing cartilaginous skeleton. Distinct positive and negative regulatory elements act together to control tissue-specific transgene expression in the developing midbrain neuroepithelium. Positive elements affecting expression in the midbrain were found in the region from -90 to -1,500 and from +701 to +2,387, whereas negatively acting elements were detected in the regions from -1,500 to -6,100 and +2,388 to +2,855.

Detection and characterization of Sp1 binding activity in human chondrocytes and its alterations during chondrocyte dedifferentiation

We have detected DNA binding activity for a synthetic oligonucleotide containing an Sp1 consensus sequence in nuclear extracts from human chondrocytes. Changes in the levels of Sp1 oligonucleotide binding activity were examined in nuclear extracts from freshly isolated human chondrocytes, from chondrocytes that had been cultured under conditions that allowed the maintenance of a chondrocyte-specific phenotype on plastic dishes coated with the hydrogel poly(2-hydroxyethyl methacrylate), and from chondrocytes induced to dedifferentiate into fibroblast-like cells by passage in monolayer culture on plastic substrata. It was observed that Sp1 binding was 2-3-fold greater in nuclear extracts from dedifferentiated chondrocytes than in nuclear extracts from either freshly isolated chondrocytes or from cells cultured in suspension. The Sp1 binding activity was specific, since it was competed by unlabeled Sp1 but not by AP1 or AP2. The addition of a polyclonal antibody against Sp1 to nuclear extracts from freshly isolated chondrocytes or to extracts isolated from chondrocytes cultured in monolayer decreased the binding of Sp1 by approximately 85%. However, when the same experiment was carried out with nuclear extracts prepared from cells cultured on poly(2-hydroxyethyl methacrylate)-coated plates, only a very slight inhibition of Sp1 binding was observed. When fragments of the COL2A1 promoter containing putative Sp1 binding sites amplified by polymerase chain reaction were examined, it was found that the amounts of DNA-protein complex formed with nuclear extracts from dedifferentiated chondrocytes were 2-3-fold greater than the amounts formed with nuclear extracts from freshly isolated chondrocytes or from cells cultured in suspension. Quantitation of DNA binding activity by titration experiments demonstrated that nuclear extracts from fibroblast-like cells contained approximately 2-fold greater Sp-1 specific binding activity than nuclear extracts from chondrocytes. The direct role of Sp1 in type II collagen gene transcription was demonstrated by co-transfection experiments of COL2A1 promoter-CAT constructs in Drosophila Schneider line L2 cells that lack Sp1 homologs. This is the first demonstration of Sp1 binding activity in human chondrocytes and of differences in Sp1 DNA binding activity between differentiated and dedifferentiated chondrocytes.

Targeted overexpression of parathyroid hormone-related peptide in chondrocytes causes chondrodysplasia and delayed endochondral bone formation

Parathyroid hormone-related peptide (PTHrP) was initially identified as a product of malignant tumors that mediates paraneoplastic hypercalcemia. It is now known that the parathyroid hormone (PTH) and PTHrP genes are evolutionarily related and that the products of these two genes share a common receptor, the PTH/PTHrP receptor. PTHrP and the PTH/PTHrP receptor are widely expressed in both adult and fetal tissues, and recent gene-targeting and disruption experiments have implicated PTHrP as a developmental regulatory molecule. Apparent PTHrP functions include the regulation of endochondral bone development, of hair follicle formation, and of branching morphogenesis in the breast. Herein, we report that overexpression of PTHrP in chondrocytes using the mouse type II collagen promoter induces a novel form of chondrodysplasia characterized by short-limbed dwarfism and a delay in endochondral ossification. This features a delay in chondrocyte differentiation and in bone collar formation and is sufficiently marked that the mice are born with a cartilaginous endochondral skeleton. In addition to the delay, chondrocytes in the transgenic mice initially become hypertrophic at the periphery of the developing long bones rather than in the middle, leading to a seeming reversal in the pattern of chondrocyte differentiation and ossification. By 7 weeks, the delays in chondrocyte differentiation and ossification have largely corrected, leaving foreshortened and misshapen but histologically near-normal bones. These findings confirm a role for PTHrP as an inhibitor of the program of chondrocyte differentiation. PTHrP may function in this regard to maintain the stepwise differentiation of chondrocytes that initiates endochondral ossification in the midsection of endochondral bones early in development and that also permits linear growth at the growth plate later in development.

Differential regulation of COL2A1 expression in developing and mature chondrocytes

To investigate the regulation of type II collagen gene expression in cells undergoing chondrogenic differentiation, we have employed a 5-kbp genomic fragment of the human type II collagen gene which contains 1.8kbp of upstream sequences, the transcription start site, the first exon and 3 kbp of intronic sequences, fused to either lac Z or chloramphenicol acetyl transferase-reporter gene. Transient expression studies revealed a parallel increase in transgene activity and endogenous type II collagen mRNA levels during the onset of the cartilage differentiation of limb mesenchymal cells in high-density micromass cultures. At later periods in culture, however, the transgene activity declines, although steady-state levels of type II collagen mRNA are reported to continue to increase (Kosher et al.: J. Cell. Biol. 102: 1151-1156, 1986; Kravis and Upholt. Dev. Biol. 108: 164-172, 1985). In addition, the activity of the transgene is seven-fold higher at the onset of chondrogenic differentiation in micromass cultures that in well differentiated sternal chondrocytes, although similar levels of type II collagen transcripts are found in these cells. Furthermore, deletions of intronic segments resulted in greater drop in activity of the constructs in differentiating chondrocytes in micromass cultures than in mature sternal chondrocytes. The expression of the construct in transgenic mice is higher at the onset of chondrogenic differentiation and in newly differentiated chondrocytes than in more mature differentiated chondrocytes. Based on these observations, it appears that the mechanisms involved in the regulation of the type II collagen gene at the onset of chondrocyte differentiation are different from those resulting in the maintenance of its expression in fully differentiated chondrocytes.

A 182 bp fragment of the mouse pro alpha 1(II) collagen gene is sufficient to direct chondrocyte expression in transgenic mice

Type II collagen is a major chondrocyte-specific component of the cartilage extracellular matrix and it represents a typical differentiation marker of mature chondrocytes. In order to delineate cis-acting elements of the mouse pro alpha 1(II) collagen gene that control chondrocyte-specific expression in intact mouse embryos, we generated transgenic mice harboring chimeric constructions in which varying lengths of the promoter and intron 1 sequences were linked to a beta-galactosidase reporter gene. A construction containing a 3,000 bp promoter and a 3,020 bp intron 1 fragment directed high levels of beta-galactosidase expression specifically to chondrocytes. Expression of the transgene coincided with the temporal expression of the endogenous gene at all stages of embryonic development. Successive deletions of intron 1 delineated a 182 bp fragment which targeted beta-galactosidase expression to chondrocytes with the same specificity as the larger intron 1 fragment. Transgenic mice harboring a 309 bp Col2a1 promoter lacking intron 1 tester sequences showed no beta-galactosidase expression in chondrocytes. Reduction of the 182 bp fragment to a 73 bp subfragment surrounding a decamer sequence previously reported to be involved in chondrocyte specificity, resulted in loss of transgene expression in chondrocytes. When the Col2a1 promoter was replaced with a minimal beta-globin promoter, the 182 bp intron 1 sequence was still able to target expression of the transgene to chondrocytes. We conclude that a 182 bp intron 1 DNA segment of the mouse Col2a1 gene contains the necessary information to confer high-level, temporally correct, chondrocyte expression on a reporter gene in intact mouse embryos and that Col2a1 promoter sequences are dispensable for chondrocyte expression.

Use of a new rat chondrosarcoma cell line to delineate a 119-base pair chondrocyte-specific enhancer element and to define active promoter segments in the mouse pro-alpha 1(II) collagen gene

We show that a new rat chondrosarcoma (RCS) cell line established in long-term culture from the Swarm tumor displayed a stable differentiated chondrocyte-like phenotype. Indeed, these cells produced the collagen types II, IX, and XI and alcian blue-stainable cartilage-specific proteoglycans, but no type I or type III collagen. To functionally characterize their chondrocytic nature, the cells were stably transfected with a type II collagen/beta geo chimeric gene which confers essentially perfect chondrocyte-specific expression in transgenic mice. RCS cells expressed both beta-galactosidase and G418 resistance, in comparison with similarly transfected 10T1/2 and NIH/3T3 fibroblasts which did not. These cells were then used to perform a systematic deletion analysis of the first intron of the mouse type II collagen gene (Col2a1) using transient expression experiments to determine which segments stimulated expression of a luciferase reporter gene in RCS cells but not in 10T1/2 fibroblasts. Cloning of two tandem copies of a 156-base pair (bp) intron 1 fragment (+2188 to +2343) in a construction containing a 314-bp Col2a1 promoter caused an almost 200-fold increase in promoter activity in RCS cells but no increase in 10T1/2 cells. DNase I footprint analysis over this 156-bp fragment revealed two adjacent protected regions, FP1 and FP2, located in the 3'-half of this segment, but no differences were seen with nuclear extracts of RCS cells and 10T1/2 fibroblasts. Deletion of FP2 to leave a 119-bp segment decreased enhancer activity by severalfold, but RCS cell specificity was maintained. Further deletions indicated that sequences both in the 5' part of the 119-bp fragment and in FP1 were needed simultaneously for RCS cell-specific enhancer activity. A series of deletions in the promoter region of the mouse Col2a1 gene progressively reduced activity when these promoters were tested by themselves in transient expression experiments. However, these promoter deletions were all activated to a similar level in RCS cells by a 231-bp intron 1 fragment that included the 156-bp enhancer. The RCS cell-specific activity persisted even if the Col2a1 promoter was replaced by a minimal adenovirus major late promoter. This 231-bp intron 1 fragment also had strong enhancing activity in transiently transfected mouse primary chondrocytes. Our experiments establish the usefulness of RCS cells as an experimental system for studies of the control of chondrocyte-specific genes, provide an extensive delineation of segments in the Col2a1 first intron involved in chondrocyte-specific activity, and show that promoter sequences are dispensable for chondrocyte specificity.

Developmental expression of a type II collagen/beta-galactosidase fusion gene in transgenic mice

The correct temporal and spatial expression of the type II collagen gene is believed to be important for normal development and growth of the skeleton and the eye, i.e., tissues where the protein product is predominantly found. To study transcriptional activation of type II collagen gene in skeletal and nonskeletal tissues we produced transgenic mice carrying murine proalpha1(II) collagen/beta-galactosidase fusion gene constructs. The expression of the fusion gene was found to depend on the presence of intron 1 deleted failed to reveal any beta-galactosidase activity confirming the important role of regulatory sequences within intron 1 of the gene. High-level expression of the functional construct was clearly confined to cartilaginous tissues but transient low-level expression was also observed in extraskeletal locations, such as the developing brain and the notochord. The results demonstrate that the regulatory elements in the proalpha1(II) collagen/beta-galactosidase fusion gene construct confer both temporal and spatial specificity indistinguishable from that of the endogenous proalpha1(II) collagen gene as determined by the presence of the corresponding mRNA by in situ hybridization. Furthermore the beta-galactosidase activity correlated well with the progression of chondrogenesis as seen by staining of whole mouse embryos with Alizarin red S and Alcian blue in the hybrid mouse strain used for microinjections. The transgenic mouse line produced should prove useful for studies on various aspects of chondrogenesis. Furthermore, the data shows that the regulatory elements present in the construct are sufficient for targetting the expression of other genes in cartilage.

Conservation of the sizes of 53 introns and over 100 intronic sequences for the binding of common transcription factors in the human and mouse genes for type II procollagen (COL2A1)

Over 11,000 bp of previously undefined sequences of the human COL2A1 gene were defined. The results made it possible to compare the intron structures of a highly complex gene from man and mouse. Surprisingly, the sizes of the 53 introns of the two genes were highly conserved with a mean difference of 13%. After alignment of the sequences, 69% of the intron sequences were identical. The introns contained consensus sequences for the binding of over 100 different transcription factors that were conserved in the introns of the two genes. The first intron of the gene contained 80 conserved consensus sequences and the remaining 52 introns of the gene contained 106 conserved sequences for the binding of transcription factors. The 5'-end of intron 2 in both genes had a potential for forming a stem loop in RNA transcripts.

Human COL2A1-directed SV40 T antigen expression in transgenic and chimeric mice results in abnormal skeletal development

The ability of SV40 T antigen to cause abnormalities in cartilage development in transgenic mice and chimeras has been tested. The cis-regulatory elements of the COL2A1 gene were used to target expression of SV40 T antigen to differentiating chondrocytes in transgenic mice and chimeras derived from embryonal stem (ES) cells bearing the same transgene. The major phenotypic consequences of transgenic (pAL21) expression are malformed skeleton, disproportionate dwarfism, and perinatal/neonatal death. Expression of T antigen was tissue specific and in the main characteristic of the mouse alpha 1(II) collagen gene. Chondrocyte densities and levels of alpha 1(II) collagen mRNAs were reduced in the transgenic mice. Islands of cells which express cartilage characteristic genes such as type IIB procollagen, long form alpha 1(IX) collagen, alpha 2(XI) collagen, and aggrecan were found in the articular and growth cartilages of pAL21 chimeric fetuses and neonates. But these cells, which were expressing T antigen, were not properly organized into columns of proliferating chondrocytes. Levels of alpha 1(II) collagen mRNA were reduced in these chondrocytes. In addition, these cells did not express type X collagen, a marker for hypertrophic chondrocytes. The skeletal abnormality in pAL21 mice may therefore be due to a retardation of chondrocyte maturation or an impaired ability of chondrocytes to complete terminal differentiation and an associated paucity of some cartilage matrix components.

Evolution of protamine P1 genes in primates

Protamine P1 genes have been sequenced by PCR amplification and direct DNA sequencing from 9 primates representing 5 major families, Cebidae (new world monkeys), Cercopithecidae (old world monkeys), Hylobatidae (gibbons), Pongidae (gorilla, orangutan, and chimpanzee), and Hominidae (human). In this recently diverged group of primates these genes are clearly orthologous but very variable, both at the DNA level and in their expressed amino acid sequences. The rate of variation amongst the protamine P1s indicates that they are amongst the most rapidly diverging polypeptides studied. However, some regions are conserved both in primates and generally in other placental mammals. These are the 13 N-terminal residues (including a region of alternating serine and arginine residues (the motif SRSR, res. 10-13) susceptible to Ser phosphorylation), a tract of six Arg residues (res. 24-29) in the center of the molecule, and a six-residue region (RCCRRR, res. 39-44), consisting of a pair of cysteines flanked by arginines. Detailed consideration of nearest-neighbor matrices and trees based on maximum parsimony indicates that P1 genes from humans, gorillas, and chimpanzees are very similar. The amino acid and nucleotide differences between humans and gorillas are fewer than those between humans and chimpanzees. This finding is at variance with data from DNA-DNA hybridization and extensive globin and mitochondrial DNA sequences which place human and chimpanzee as closest relatives in the super family, Hominoidea. This may be related to the fact that protamine P1s are expressed in germ line rather than somatic cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Early-onset osteoarthritis linked to the type II procollagen gene. Detailed clinical phenotype and further analyses of the gene

OBJECTIVE

To specify in detail the clinical phenotype in 2 Finnish families demonstrating linkage between the type II procollagen gene (COL2A1) and osteoarthritis (OA). We also reevaluated the linkage and screened the exon sequences of the COL2A1 gene for mutations.

METHODS

We used single-stranded conformation polymorphism and denaturing gradient-gel electrophoresis techniques for the analyses.

RESULTS

The patients' phenotype represented typical, but early-onset, OA. There was no clinical or radiographic evidence of chondrodysplasia. No mutation in the protein-coding regions of the COL2A1 gene could be identified. However, the linkage analysis with a new multiallelic marker resulted in a statistically more significant logarithm of odds (LOD) score than has been reported.

CONCLUSION

Familial OA with classic clinical and radiographic findings is tightly linked to the COL2A1 gene. Systematic screening of the 54 exons did not, however, reveal any mutations; this suggests that the mutation may lie in the promoter region or within the introns of this 35-kb gene.