Matrilin-1 is essential for zebrafish development by facilitating collagen II secretion.

Matrilin-1 is the prototypical member of the matrilin protein family and is highly expressed in cartilage. However, gene targeting of matrilin-1 in mouse did not lead to pronounced phenotypes. Here we used the zebrafish as an alternative model to study matrilin function in vivo. Matrilin-1 displays a multiphasic expression during zebrafish development. In an early phase, with peak expression at about 15 h post-fertilization, matrilin-1 is present throughout the zebrafish embryo with exception of the notochord. Later, when the skeleton develops, matrilin-1 is expressed mainly in cartilage. Morpholino knockdown of matrilin-1 results both in overall growth defects and in disturbances in the formation of the craniofacial cartilage, most prominently loss of collagen II deposition. In fish with mild phenotypes, certain cartilage extracellular matrix components were present, but the tissue did not show features characteristic for cartilage. The cells showed endoplasmic reticulum aberrations but no activation of XBP-1, a marker for endoplasmic reticulum stress. In severe phenotypes nearly all chondrocytes died. During the early expression phase the matrilin-1 knockdown had no effects on cell morphology, but increased cell death was observed. In addition, the broad deposition of collagen II was largely abolished. Interestingly, the early phenotype could be rescued by the co-injection of mRNA coding for the von Willebrand factor C domain of collagen IIα1a, indicating that the functional loss of this domain occurs as a consequence of matrilin-1 deficiency. The results show that matrilin-1 is indispensible for zebrafish cartilage formation and plays a role in the early collagen II-dependent developmental events.

Identification of a Ninein (NIN) mutation in a family with spondyloepimetaphyseal dysplasia with joint laxity (leptodactylic type)-like phenotype.

Spondyloepimetaphyseal dysplasia with joint laxity-leptodactylic type (SEMDJL2) is an autosomal dominant skeletal dysplasia which is characterized by midface hypoplasia, short stature, joint laxity with dislocations, genua valga, progressive scoliosis, and slender fingers. Recently, heterozygous missense mutations in KIF22, a gene which encodes a member of the kinesin-like protein family, have been identified in sporadic as well as familial cases of SEMDJL2. In the present study homozygosity mapping and whole-exome sequencing were combined to analyze a consanguineous family with a phenotype resembling SEMDJL2. We identified homozygous missense mutations in the two nearby genes NIN (Ninein) and POLE2 (DNA polymerase epsilon subunit B) which segregate with the disease in the family and were not present in 500 healthy control individuals and in the 1094 control individuals contained within the 1000-genomes database. We present several lines of evidence that mutant Ninein is most likely causative for the SEMDJL2-like phenotype. The centrosomal protein NIN shows a functional relationship with KIF22 and other proteins associated with chromosome congression/movement, centrosomal function, and ciliogenesis, which have been associated with skeletal dysplasias. Moreover, compound heterozygous missense mutations at more N-terminal positions of Ninein have very recently been identified in a family with microcephalic primordial dwarfism. Together with the present report this strongly supports a fundamental role of Ninein in skeletal development.

Selenoprotein M is expressed during bone development.

25 selenoproteins that contain selenium, incorporated as selenocysteine (Sec), have been identified to date. Selenoprotein M (SELM) is one of seven endoplasmic reticulum (ER)-resident, Sec-containing proteins that may be involved in posttranslational processing of proteins and maintenance of ER function. Since SELM was overrepresented in a cartilage- and bone-specific expressed sequence tag (EST) library, we further investigated the expression pattern of Selm and its possible biological function in the skeleton. RNA in situ hybridization of Selm in chicken and mice of different developmental stages revealed prominent expression in bones, specifically in osteoblast, and in tendons. This result suggests that SELM functions during bone development, where it is possibly involved in the processing of secreted proteins.

Ucmaa (Grp-2) is required for zebrafish skeletal development. Evidence for a functional role of its glutamate γ-carboxylation.

UCMA (alternatively named GRP) is a novel member of the family of γ-carboxyglutamate (Gla) containing proteins that is mainly expressed in cartilage. We have used the zebrafish as a model organism to study UCMA function. Due to the whole genome duplication two Ucma genes are present in zebrafish, ucmaa and ucmab, located on chromosomes 25 and 4, respectively. UCMA gene structure, alternative splicing and protein sequence are highly conserved between mammals and zebrafish and Ucmaa and Ucmab are expressed in zebrafish skeletal tissues. Ucmaa is first detected in the notochord at 18 hpf and expression continues during notochord development. In addition, it is widely present in the developing craniofacial cartilage. In contrast, the weakly expressed Ucmab can be first detected at specific sites in the craniofacial cartilage at 96 hpf, but not in notochord. Knockdown of ucmaa leads to severe growth retardation and perturbance of skeletal development. The cartilage of the morphants has a decreased aggrecan and collagen II content. Similar malformations were observed when glutamate γ-carboxylation was inhibited by warfarin treatment, indicating that glutamate γ-carboxylation is crucial for Ucma function and pointing to a role of UCMA in the pathogenesis of "warfarin embryopathies" and other human skeletal diseases.

Disruption of ST5 is associated with mental retardation and multiple congenital anomalies.

BACKGROUND: The authors observed a patient with a cryptic subtelomeric de novo balanced translocation 46,XY.ish t(11;20)(p15.4;q13.2) presenting with severe mental retardation, muscular hypotonia, seizures, bilateral sensorineural hearing loss, submucous cleft palate, persistent ductus Botalli, unilateral cystic kidney dysplasia and frequent infections. METHODS AND RESULTS: Fluorescence in situ hybridisation mapping and sequencing of the translocation breakpoints showed that no known genes are disrupted at 20q13.2 and that ST5 (suppression of tumorigenicity 5; MIM 140750) is disrupted on 11p15.4. By quantitative PCR from different human tissues, the authors found ST5 to be relatively evenly expressed in fetal tissues. ST5 expression was more pronounced in adult brain, kidney and muscle than in the corresponding fetal tissues, whereas expression in other tissues was generally lower than in the fetal tissue. Using RNA in situ hybridisation in mouse, the authors found that St5 is expressed in the frontal cortex during embryonic development. In adult mouse brain, expression of St5 was especially high in the hippocampal area and cerebellum. CONCLUSION: Hence, the authors suppose that ST5 plays an important role in central nervous system development probably due to disturbance of DENN-domain-mediated vesicle formation and neurotransmitter trafficking. Thus, these findings implicate ST5 in the aetiology of mental retardation, seizures and multiple congenital anomalies.

Ucma, a novel secreted cartilage-specific protein with implications in osteogenesis.

Here we report on the structure, expression, and function of a novel cartilage-specific gene coding for a 17-kDa small, highly charged, and secreted protein that we termed Ucma (unique cartilage matrix-associated protein). The protein is processed by a furin-like protease into an N-terminal peptide of 37 amino acids and a C-terminal fragment (Ucma-C) of 74 amino acids. Ucma is highly conserved between mouse, rat, human, dog, clawed frog, and zebrafish, but has no homology to other known proteins. Remarkable are 1-2 tyrosine sulfate residues/molecule and dense clusters of acidic and basic residues in the C-terminal part. In the developing mouse skeleton Ucma mRNA is expressed in resting chondrocytes in the distal and peripheral zones of epiphyseal and vertebral cartilage. Ucma is secreted into the extracellular matrix as an uncleaved precursor and shows the same restricted distribution pattern in cartilage as Ucma mRNA. In contrast, antibodies prepared against the processed C-terminal fragment located Ucma-C in the entire cartilage matrix, indicating that it either diffuses or is retained until chondrocytes reach hypertrophy. During differentiation of an MC615 chondrocyte subclone in vitro, Ucma expression parallels largely the expression of collagen II and decreases with maturation toward hypertrophic cells. Recombinant Ucma-C does not affect expression of chondrocyte-specific genes or proliferation of chondrocytes, but interferes with osteogenic differentiation of primary osteoblasts, mesenchymal stem cells, and MC3T3-E1 pre-osteoblasts. These findings suggest that Ucma may be involved in the negative control of osteogenic differentiation of osteochondrogenic precursor cells in peripheral zones of fetal cartilage and at the cartilage-bone interface.

Ucma--A novel secreted factor represents a highly specific marker for distal chondrocytes.

Growth and development of most parts of the vertebrate skeleton takes place by endochondral ossification, a process during which chondrocytes undergo distinct stages of differentiation resulting in a successive replacement of the cartilage anlagen by bone. In the context of an EST project we isolated a novel transcript from a human fetal growth plate cartilage cDNA library. The transcript which we called Ucma (unique cartilage matrix-associated protein) encodes a short protein of 138 amino acids. The protein sequence is evolutionary conserved throughout vertebrates and comprises a signal peptide, a coiled-coil domain, and a putative dibasic cleavage site for proprotein convertases. Using RNA in situ hybridization and immunohistochemistry with a polyclonal anti-Ucma antibody we found high expression of Ucma uniquely in distal (resting) chondrocytes in developing long bones of wildtype mice. This restricted expression could also be observed in Ihh(-/-), Ihh(-/-); Gli3(-/-), Gli3(-/-) mice, and in mice that overexpress Ihh under the control of the Col2a1 promoter indicating that expression of Ucma is regulated independent of hedgehog signaling. During insulin-induced differentiation of ATDC5 cells we found gradual increase of Ucma expression at day 21 with a maximum at day 24 and a decrease correlating with a simultaneous increase in the expression of cartilage link protein (Crtl1), a protein with maximum expression in column-forming proliferating chondrocytes. The present data strongly suggest an important function of Ucma in the early phase of chondrocyte differentiation.

Differential proteome analysis of colon carcinoma cell line SW480 after reconstitution of the tumour suppressor Smad4.

The tumour suppressor gene Smad4 is frequently inactivated in gastrointestinal carcinomas. Smad4 plays a pivotal role in transducing signals of the transforming growth factor-beta (TGF-beta) superfamily of proteins. Inactivation of Smad4 seems to occur late during tumour progression when tumours acquire invasive and metastatic properties. Identification of proteins directly or indirectly regulated by Smad4 would, therefore, ease the future design of new diagnostic and therapeutic strategies for gastrointestinal carcinoma. We have used human colon carcinoma cell line SW480 stably transfected with Smad4 as an in-vitro model system to identify Smad4-regulated proteins by applying two-dimensional gel electrophoresis (2DE) then MALDI-PMF/PFF-MS. We identified a total of 47 protein species with a Smad4-dependent expression. From the functions of the candidate proteins we obtained new insights into Smad4's participation in processes, for example apoptosis, differentiation, and proliferation.

Deficiency of UBR1, a ubiquitin ligase of the N-end rule pathway, causes pancreatic dysfunction, malformations and mental retardation (Johanson-Blizzard syndrome).

Johanson-Blizzard syndrome (OMIM 243800) is an autosomal recessive disorder that includes congenital exocrine pancreatic insufficiency, multiple malformations such as nasal wing aplasia, and frequent mental retardation. We mapped the disease-associated locus to chromosome 15q14-21.1 and identified mutations, mostly truncating ones, in the gene UBR1 in 12 unrelated families with Johanson-Blizzard syndrome. UBR1 encodes one of at least four functionally overlapping E3 ubiquitin ligases of the N-end rule pathway, a conserved proteolytic system whose substrates include proteins with destabilizing N-terminal residues. Pancreas of individuals with Johanson-Blizzard syndrome did not express UBR1 and had intrauterine-onset destructive pancreatitis. In addition, we found that Ubr1(-/-) mice, whose previously reported phenotypes include reduced weight and behavioral abnormalities, had an exocrine pancreatic insufficiency, with impaired stimulus-secretion coupling and increased susceptibility to pancreatic injury. Our findings indicate that deficiency of UBR1 perturbs the pancreas' acinar cells and other organs, presumably owing to metabolic stabilization of specific substrates of the N-end rule pathway.

Expression profiling of human fetal growth plate cartilage by EST sequencing.

The differentiation of mesenchymal stem cells into hypertrophic chondrocytes is an integral and multistep process important in pattern formation, endochondral ossification, and postnatal growth of the skeleton. In recent years, novel genes involved in these processes have been identified, but still only little is known about the large-scale gene expression profile during skeletal development. We initiated an expressed sequence tag (EST) project aiming at the identification of genes and pathways involved in this complex process. Candidate genes are expected to be of value for diagnosis and treatment of monogenic and multigenic heritable disorders of the skeleton. Here, we describe the sequences of 4,748 clones from a human growth plate cartilage cDNA library generated from 20 weeks prenatal-2 years postnatal specimens. In silico analysis of these sequences revealed 1,688 individual transcription units, corresponding to known (1,274) and to novel, yet uncharacterised potential genes (414). The tissue specificity of the library was reflected by its corresponding EST profile representing a total of approximately 10% proteins already shown to be involved in cartilage/bone development or homeostasis. The EST profile also reflects the developmental stage of the tissue with significant differences in the expression of matrix proteins compared to corresponding EST profiles from 8-12 and 12-20 week human fetal cartilage. Calculation of the relative frequency of transcripts in our cDNA library, as compared to their abundance in other EST datasets, revealed a set of approximately 200 genes, including 81 novel, yet uncharacterised genes, showing increased expression. These genes represent candidates for the large number of osteochondrodysplasias for which the causative gene defects have not yet been identified.

A dual phenotype of periventricular nodular heterotopia and frontometaphyseal dysplasia in one patient caused by a single FLNA mutation leading to two functionally different aberrant transcripts.

Two disorders, periventricular nodular heterotopia (PVNH) and a group of skeletal dysplasias belonging to the oto-palato-digital (OPD) spectrum, are caused by FLNA mutations. They are considered mutually exclusive because of the different presumed effects of the respective FLNA gene mutations, leading to loss of function (PVNH) and gain of function (OPD), respectively. We describe here the first patient manifesting PVNH in combination with frontometaphyseal dysplasia, a skeletal dysplasia of the OPD-spectrum. A novel de novo mutation, 7315C-->A in exon 45 of the FLNA gene, was identified. It leads to two aberrant transcripts, one full-length transcript with the point mutation causing a substitution of a highly conserved leucine residue (L2439M) and a second shortened transcript lacking 21 bp due to the creation of an ectopic splice donor site in exon 45. We propose that the dual phenotype is caused by two functionally different, aberrant filamin A proteins and therefore represents an exceptional model case of allelic gain-of-function and loss-of-function phenotypes due to a single mutational event.