The structural genes for alpha 1 and alpha 2 chains of human type IV collagen are divergently encoded on opposite DNA strands and have an overlapping promoter region

Quantitative Real-Time RT-PCR Verifying Gene Expression Profile of Cavitations Within Human Jaw Bone

Background/Objectives: Immune cells are integral to bone homeostasis, including the repair and remodeling of bone tissue. Chronic dysregulation within this osteoimmune network can lead to bone marrow defects of the jaw (BMDJ), particularly fatty degenerative osteonecrosis of the jaw (FDOJ). These localized pathologies are implicated in systemic immune dysfunctions. Methods: This study is designed to determine whether BMDJ/FDOJ samples are indicative of medullary bone pathology by evaluating FDOJ gene expression patterns using quantitative real-time PCR. Results: Comparative analyses between pathological and healthy samples evaluated the dysregulation of key molecular pathways. BMDJ/FDOJ samples showed significant upregulation of inflammatory mediators, including CCL5/RANTES, VEGF, IGF and KOR, and downregulation of structural proteins, such as collagen types I, II and IV, and osteogenesis-associated factors, such as SP7. Conclusions: The study provides new insights into the molecular mechanisms of BMDJ/FDOJ by identifying potential molecular changes suggesting a pro-inflammatory state in the affected jawbone which may contribute to systemic immune dysregulation. The findings are consistent with morphologic observations of BMDJ/FDOJ in degenerated jawbone and underscore the need for integrative approaches in dentistry and medicine while highlighting BMDJ/FDOJ as a potential target for therapeutic and preventive strategies against systemic diseases and emphasizing its clinical significance.

Characterization of cell cycle, inflammation, and oxidative stress signaling role in non-communicable diseases: Insights into genetic variants, microRNAs and pathways

Non-Communicable Diseases (NCDs) significantly impact global health, contributing to over 70% of premature deaths, as reported by the World Health Organization (WHO). These diseases have complex and multifactorial origins, involving genetic, epigenetic, environmental and lifestyle factors. While Genome-Wide Association Study (GWAS) is widely recognized as a valuable tool for identifying variants associated with complex phenotypes; the multifactorial nature of NCDs necessitates a more comprehensive exploration, encompassing not only the genetic but also the epigenetic aspect. For this purpose, we employed a bioinformatics-multiomics approach to examine the genetic and epigenetic characteristics of NCDs (i.e. colorectal cancer, coronary atherosclerosis, squamous cell lung cancer, psoriasis, type 2 diabetes, and multiple sclerosis), aiming to identify novel biomarkers for diagnosis and prognosis. Leveraging GWAS summary statistics, we pinpointed Single Nucleotide Polymorphisms (SNPs) independently associated with each NCD. Subsequently, we identified genes linked to cell cycle, inflammation and oxidative stress mechanisms, revealing shared genes across multiple diseases, suggesting common functional pathways. From an epigenetic perspective, we identified microRNAs (miRNAs) with regulatory functions targeting these genes of interest. Our findings underscore critical genetic pathways implicated in these diseases. In colorectal cancer, the dysregulation of the "Cytokine Signaling in Immune System" pathway, involving LAMA5 and SMAD7, regulated by Hsa-miR-21-5p, Hsa-miR-103a-3p, and Hsa-miR-195-5p, emerged as pivotal. In coronary atherosclerosis, the pathway associated with "binding of TCF/LEF:CTNNB1 to target gene promoters" displayed noteworthy implications, with the MYC factor controlled by Hsa-miR-16-5p as a potential regulatory factor. Squamous cell lung carcinoma analysis revealed significant pathways such as "PTK6 promotes HIF1A stabilization," regulated by Hsa-let-7b-5p. In psoriasis, the "Endosomal/Vacuolar pathway," involving HLA-C and Hsa-miR-148a-3p and Hsa-miR-148b-3p, was identified as crucial. Type 2 Diabetes implicated the "Regulation of TP53 Expression" pathway, controlled by Hsa-miR-106a-5p and Hsa-miR-106b-5p. In conclusion, our study elucidates the genetic framework and molecular mechanisms underlying NCDs, offering crucial insights into potential genetic/epigenetic biomarkers for diagnosis and prognosis. The specificity of pathways and related miRNAs in different pathologies highlights promising candidates for further clinical validation, with the potential to advance personalized treatments and alleviate the global burden of NCDs.

Collagen type IV alpha 1 chain (COL4A1) expression in the developing human lung

BACKGROUND

Collagen type IV alpha 1 chain (COL4A1) in the basement membrane is an important component during lung development, as suggested from animal models where COL4A1 has been shown to regulate alveolarization and angiogenesis. Less is known about its role in human lung development. Our aim was to study COL4A1 expression in preterm infants with different lung maturational and clinical features.

METHODS

COL4A1 expression in 115 lung samples from newborn infants (21-41 weeks' gestational age; 0-228 days' postnatal age [PNA]) was studied by immunohistochemistry combined with digital image analysis. Cluster analysis was performed to find subgroups according to immunohistologic and clinical data.

RESULTS

Patients were automatically categorized into 4 Groups depending on their COL4A1 expression. Expression of COL4A1 was mainly extracellular in Group 1, low in Group 2, intracellular in Group 3, and both extra- and intracellular in Group 4. Intracellular/extracellular ratio of COL4A1 expression related to PNA showed a distinctive postnatal maturational pattern on days 1-7, where intracellular expression of COL4A1 was overrepresented in extremely preterm infants.

CONCLUSIONS

COL4A1 expression seems to be highly dynamic during the postnatal life due to a possible rapid remodeling of the basement membrane. Intracellular accumulation of COL4A1 in the lungs of extremely premature infants occurs more frequently between 1 and 7 postnatal days than during the first 24 hours. In view of the lung arrest described in extremely preterm infants, the pathological and/or developmental role of postnatally increased intracellular COL4A1 as marker for basement membrane turnover, needs to be further investigated.

A novel nanoluciferase transgenic reporter measures proteinuria in zebrafish

The zebrafish is an important animal system for modeling human diseases. This includes kidney dysfunction as the embryonic kidney (pronephros) shares considerable molecular and morphological homology with the human nephron. A key clinical indicator of kidney disease is proteinuria, but a high-throughput readout of proteinuria in the zebrafish is currently lacking. To remedy this, we used the Tol2 transposon system to generate a transgenic zebrafish line that uses the fabp10a liver-specific promoter to over-express a nanoluciferase molecule fused with the D3 domain of Receptor-Associated Protein (a type of molecular chaperone) which we term NL-D3. Using a luminometer, we quantified proteinuria in NL-D3 zebrafish larvae by measuring the intensity of luminescence in the embryo medium. In the healthy state, NL-D3 is not excreted, but when embryos were treated with chemicals that affected either proximal tubular reabsorption (cisplatin, gentamicin) or glomerular filtration (angiotensin II, Hanks Balanced Salt Solution, Bovine Serum Albumin), NL-D3 is detected in fish medium. Similarly, depletion of several gene products associated with kidney disease (nphs1, nphs2, lrp2a, ocrl, col4a3, and col4a4) also induced NL-D3 proteinuria. Treating col4a4 depleted zebrafish larvae (a model of Alport syndrome) with captopril reduced proteinuria in this system. Thus, our findings validate the use of the NL-D3 transgenic zebrafish as a robust and quantifiable proteinuria reporter. Hence, given the feasibility of high-throughput assays in zebrafish, this novel reporter will permit screening for drugs that ameliorate proteinuria, thereby prioritizing candidates for further translational studies.

A novel nanoluciferase transgenic reporter measures proteinuria in zebrafish

The zebrafish is an important animal system for modeling human diseases. This includes kidney dysfunction as the embryonic kidney (pronephros) shares considerable molecular and morphological homology with the human nephron. A key clinical indicator of kidney disease is proteinuria, but a high-throughput readout of proteinuria in the zebrafish is currently lacking. To remedy this, we used the Tol2 transposon system to generate a transgenic zebrafish line that uses the fabp10a liver-specific promoter to over-express a nanoluciferase molecule fused with the D3 domain of Receptor-Associated Protein (a type of molecular chaperone) which we term NL-D3. Using a luminometer, we quantified proteinuria in NL-D3 zebrafish larvae by measuring the intensity of luminescence in the embryo medium. In the healthy state, NL-D3 is not excreted, but when embryos were treated with chemicals that affected either proximal tubular reabsorption (cisplatin, gentamicin) or glomerular filtration (angiotensin II, Hanks Balanced Salt Solution, Bovine Serum Albumin), NL-D3 is detected in fish medium. Similarly, depletion of several gene products associated with kidney disease (nphs1, nphs2, lrp2a, ocrl, col4a3, and col4a4) also induced NL-D3 proteinuria. Treating col4a4 depleted zebrafish larvae (a model of Alport syndrome) with captopril reduced proteinuria in this system. Thus, our findings validate the use of the NL-D3 transgenic zebrafish as a robust and quantifiable proteinuria reporter. Hence, given the feasibility of high-throughput assays in zebrafish, this novel reporter will permit screening for drugs that ameliorate proteinuria, thereby prioritizing candidates for further translational studies.

Collagen IV (COL4A1, COL4A2), a Component of the Viral Biofilm, Is Induced by the HTLV-1 Oncoprotein Tax and Impacts Virus Transmission

Human T-cell leukemia virus type 1 (HTLV-1) is the etiologic agent for Adult T-Cell Leukemia/Lymphoma (ATLL) and HTLV-1-Associated Myelopathy/Tropical Spastic Paraparesis (HAM/TSP). HTLV-1 infects CD4⁺ T-cells via cell-to-cell transmission requiring reorganization of the cytoskeleton and expression of the viral transactivator and oncoprotein Tax. Viruses spread at the virological synapse (VS), a virus-induced specialized cell-cell contact, by polarized budding into synaptic clefts, and by cell surface transfer of viral biofilms (VBs). Since little is known about Tax’s role in formation of the VB, we asked which component of the VB is regulated by Tax and important for HTLV-1 transmission. Collagens are not only structural proteins of the extracellular matrix and basal membrane but also represent an important component of the VB. Here, we report that among the collagens known to be present in VBs, COL4 is specifically upregulated in the presence of HTLV-1 infection. Further, we found that transient expression of Tax is sufficient to induce COL4A1 and COL4A2 transcripts in Jurkat and CCRF-CEM T-cells, while robust induction of COL4 protein requires continuous Tax expression as shown in Tax-transformed T-cell lines. Repression of Tax led to a significant reduction of COL4A1/A2 transcripts and COL4 protein. Mechanistically, luciferase-based promoter studies indicate that Tax activates the COL4A2 and, to a less extent, the COL4A1 promoter. Imaging showing partial co-localization of COL4 with the viral Gag protein in VBs at the VS and transfer of COL4 and Gag to target cells suggests a role of COL4 in VB formation. Strikingly, in chronically infected C91-PL cells, knockout of COL4A2 impaired Gag transfer between infected T-cells and acceptor T-cells, while release of virus-like particles was unaffected. Taken together, we identified COL4 (COL4A1, COL4A2) as a component of the VB and a novel cellular target of Tax with COL4A2 appearing to impact virus transmission. Thus, this study is the first to provide a link between Tax’s activity and VB formation by hijacking COL4 protein functions.

Basement membrane and stroke

Located at the interface of the circulation system and the CNS, the basement membrane (BM) is well positioned to regulate blood-brain barrier (BBB) integrity. Given the important roles of BBB in the development and progression of various neurological disorders, the BM has been hypothesized to contribute to the pathogenesis of these diseases. After stroke, a cerebrovascular disease caused by rupture (hemorrhagic) or occlusion (ischemic) of cerebral blood vessels, the BM undergoes constant remodeling to modulate disease progression. Although an association between BM dissolution and stroke is observed, how each individual BM component changes after stroke and how these components contribute to stroke pathogenesis are mostly unclear. In this review, I first briefly introduce the composition of the BM in the brain. Next, the functions of the BM and its major components in BBB maintenance under homeostatic conditions are summarized. Furthermore, the roles of the BM and its major components in the pathogenesis of hemorrhagic and ischemic stroke are discussed. Last, unsolved questions and potential future directions are described. This review aims to provide a comprehensive reference for future studies, stimulate the formation of new ideas, and promote the generation of new genetic tools in the field of BM/stroke research.

Subcutaneous Injection of Nitroglycerin at the Radial Artery Puncture Site Reduces the Risk of Early Radial Artery Occlusion After Transradial Coronary Catheterization: A Randomized, Placebo-Controlled Clinical Trial

BACKGROUND

Transradial coronary catheterization is widely used as a diagnostic or interventional procedure for coronary disease. However, it can lead to adverse complications, such as radial artery occlusion. We sought to determine whether preprocedural injection of nitroglycerin at the radial artery puncture site reduces radial artery occlusion.

METHODS AND RESULTS

A total of 188 patients undergoing transradial coronary catheterization were randomized in a single-blind fashion to receive subcutaneous injection of 0.5 mL 0.1% nitroglycerin or a placebo at the radial artery puncture site. The participants underwent ultrasound examinations of the radial artery before and at 24 hours after the procedure. Of the 188 patients enrolled, 182 completed the study, as the procedure failed in 2 participants in the nitroglycerin-treated group and 4 in the placebo group. Baseline demographic and clinical characteristics were similar between 2 groups. Comparing the radial artery diameters before and after the operation, there was a statistically significant increase in the nitroglycerin-treated group (2.48±0.45 versus 2.45±0.46 mm; P=0.003) but a decrease in the placebo control group (2.41±0.50 versus 2.46±0.49 mm; P<0.001). Importantly, the incidence of radial arterial occlusion was substantially lower in the nitroglycerin-treated group than in the placebo control group (5.4% versus 14.4%; P=0.04). There was not significant difference in other complications (forearm hematoma and radial artery pseudoaneurysm, respectively), and there was no incidence of cause hypotension or an intolerable headache.

CONCLUSIONS

Subcutaneous injection of nitroglycerin at the radial artery puncture site dilates the radial artery and reduces the incidence of early radial artery occlusion post-catheterization.

CLINICAL TRIAL REGISTRATION

URL: https://www.chictr.org.cn. Unique identifier: ChiCTR-IPR-15006559.

Coronary-Heart-Disease-Associated Genetic Variant at the COL4A1/COL4A2 Locus Affects COL4A1/COL4A2 Expression, Vascular Cell Survival, Atherosclerotic Plaque Stability and Risk of Myocardial Infarction

Genome-wide association studies have revealed an association between coronary heart disease (CHD) and genetic variation on chromosome 13q34, with the lead single nucleotide polymorphism rs4773144 residing in the COL4A2 gene in this genomic region. We investigated the functional effects of this genetic variant. Analyses of primary cultures of vascular smooth muscle cells (SMCs) and endothelial cells (ECs) from different individuals showed a difference between rs4773144 genotypes in COL4A2 and COL4A1 expression levels, being lowest in the G/G genotype, intermediate in A/G and highest in A/A. Chromatin immunoprecipitation followed by allelic imbalance assays of primary cultures of SMCs and ECs that were of the A/G genotype revealed that the G allele had lower transcriptional activity than the A allele. Electrophoretic mobility shift assays and luciferase reporter gene assays showed that a short DNA sequence encompassing the rs4773144 site interacted with a nuclear protein, with lower efficiency for the G allele, and that the G allele sequence had lower activity in driving reporter gene expression. Analyses of cultured SMCs from different individuals demonstrated that cells of the G/G genotype had higher apoptosis rates. Immunohistochemical and histological examinations of ex vivo atherosclerotic coronary arteries from different individuals disclosed that atherosclerotic plaques with the G/G genotype had lower collagen IV abundance and thinner fibrous cap, a hallmark of unstable, rupture-prone plaques. A study of a cohort of patients with angiographically documented coronary artery disease showed that patients of the G/G genotype had higher rates of myocardial infarction, a phenotype often caused by plaque rupture. These results indicate that the CHD-related genetic variant at the COL4A2 locus affects COL4A2/COL4A1 expression, SMC survival, and atherosclerotic plaque stability, providing a mechanistic explanation for the association between the genetic variant and CHD risk.

Efficient Targeted Next Generation Sequencing-Based Workflow for Differential Diagnosis of Alport-Related Disorders

Alport syndrome (AS) is an inherited type IV collagen nephropathies characterized by microscopic hematuria during early childhood, the development of proteinuria and progression to end-stage renal disease. Since choosing the right therapy, even before the onset of proteinuria, can delay the onset of end-stage renal failure and improve life expectancy, the earliest possible differential diagnosis is desired. Practically, this means the identification of mutation(s) in COL4A3-A4-A5 genes. We used an efficient, next generation sequencing based workflow for simultaneous analysis of all three COL4A genes in three individuals and fourteen families involved by AS or showing different level of Alport-related symptoms. We successfully identified mutations in all investigated cases, including 14 unpublished mutations in our Hungarian cohort. We present an easy to use unified clinical/diagnostic terminology and workflow not only for X-linked but for autosomal AS, but also for Alport-related diseases. In families where a diagnosis has been established by molecular genetic analysis, the renal biopsy may be rendered unnecessary.

Basement membranes in development and disease

Basement membranes (BMs) are specializations of the extracellular matrix that act as key mediators of development and disease. Their sheet like protein matrices typically serve to separate epithelial or endothelial cell layers from underlying mesenchymal tissues, providing both a biophysical support to overlying tissue as well as a hub to promote and regulate cell-cell and cell-protein interactions. In the latter context, the BM is increasingly being recognized as a mediator of growth factor interactions during development. In this review, we discuss recent findings regarding the structure of the BM and its roles in mediating the normal development of the embryo, and we examine congenital diseases affecting the BM which impact embryonic development and health in later life.

The intergenic region between the Mouse Recql4 and Lrrc14 genes functions as an evolutionary conserved bidirectional promoter

Mammalian genomes are highly complex, with neighbouring genes arranged in divergent, convergent, tandem, antisense, and interleaving fashions. Despite the vast genomic space, a substantial portion of human genes (approximately 10%) are arranged in a divergent, head-to-head fashion and controlled by bidirectional promoters. Here we define a small core bidirectional promoter that drives expression of the mouse genes Recql4, on one strand, and Lrrc14; a novel member of the LRR gene family, on the opposite strand. Regulation of Lrrc14 expression is highly complex, involving multiple promoters' and alternative splicing. Expression of this gene is predominately restricted to neural tissue during embryogenesis and is expressed in a wide range of tissues in the adult.

Inhibition of tumor angiogenesis by tumstatin: insights into signaling mechanisms and implications in cancer regression

Growing tumors develop additional new blood vessels to meet the demand for adequate nutrients and oxygen, a process called angiogenesis. Cancer is a highly complex disease promoted by excess angiogenesis; interfering with this process poses for an attractive approach for controlling tumor growth. This hypothesis led to the identification of endogenous angiogenesis inhibitors generated from type IV collagen, a major component of vascular basement membrane (VBM). Type IV collagen and the angiogenesis inhibitors derived from it are involved in complex roles, than just the molecular construction of basement membranes. Protease degradation of collagens in VBM occurs in various physiological and pathological conditions and produces several peptides. Some of these peptides are occupied in the regulation of functions conflicting from those of their original integral molecules. Tumstatin (alpha3(IV)NC1), a proteolytic C-terminal non-collagenous (NC1) domain from type IV collagen alpha3 chain has been highlighted recently because of its potential role in anti-angiogenesis, however its biological actions are not limited to these processes. alpha3(IV)NC1 inhibits proliferation by promoting endothelial cell apoptosis and suppresses diverse tumor angiogenesis, thus making it a potential candidate for future cancer therapy. The present review surveys the physiological functions of type IV collagen and discovery of alpha3(IV)NC1 as an antiangiogenic protein with a comprehensive overview of the knowledge gained by us towards understanding its signaling mechanisms.

SRY-related HMG box 9 regulates the expression of Col4a2 through transactivating its enhancer element in mesangial cells

Accumulation of alpha1(IV) and alpha2(IV) collagen is one of the characteristic pathological changes in glomerulosclerosis. Although the Col4a2 gene is known to have a 0.3-kb critical enhancer element with the GAACAAT motif, which transcription factor binds and transactivates this motif has not been identified. In this study, we found that SRY-related HMG box 9 (SOX9) was bound to the GAACAAT motif in the Col4a2 enhancer in vitro and in vivo in mesangial cells. SOX9 strongly activated this enhancer when cotransfected with Col4a2 enhancer-promoter construct in mesangial cells and Swiss/3T3 cells. Mutation in the GAACAAT motif eliminated the activation by SOX9. Furthermore, transforming growth factor-beta (TGF-beta) treatment induced the expression of SOX9 and Col4a2, and a small interfering RNA against SOX9 reduced Col4a2 expression induced by TGF-beta treatment in mesangial cells. In vivo, we found that the expression of SOX9 was dramatically increased along with the expression of TGF-beta and Col4a2 in mouse nephrotoxic nephritis. These results indicate that SOX9 is essential for Col4a2 expression in mesangial cells and might be involved in the accumulation of alpha2(IV) collagen in experimental nephritis.

[Alport syndrome or progressive hereditary nephritis with hearing loss]

Alport syndrome is an inherited disorder characterized by progressive hematuric nephritis with structural defects of the glomerular basement membrane, and sensorineural deafness. Ocular abnormalities are frequently associated. The incidence is approximatively 1/5000. The renal disease is severe in male patients and should be responsible for 2% of end-stage renal failure. Alport syndrome is heterogeneous at the clinical and genetic levels. It occurs as a consequence of structural abnormalities in type IV collagen, the major constituent of basement membranes. Six genetically distinct chains of type IV collagen have been identified. Mutations in the COL4A5 gene located at Xq22, and encoding the alpha 5(IV) chain are responsible for X-linked Alport syndrome whereas COL4A3 or COL4A4 located "head to head" on chromosome 2 are involved in the rarer autosomal forms of the disease.

A promoter with bidirectional activity is located between TLX1/HOX11 and a divergently transcribed novel human gene

The chromosomal region 10q24 is involved in reciprocal translocations with one of the T-cell receptor loci in a significant proportion of human T-cell acute lymphoblastic leukemias. The breakpoints of these rearrangements cluster immediately upstream of the TLX1 homeobox gene and lead to its transcriptional activation. Genomic analysis using sequences located on the opposite side of the breakpoint cluster region identified a novel gene composed of three exons that is oriented in a head-to-head manner with TLX1. The novel gene, named TDI (TLX1 divergent) codes for a 1.9 kb transcript with an atypically long 5' leader sequence. Although predicted to be a transcriptional regulator of 13.4 kDa, the TDI protein has no significant sequence similarity to any known protein. The TLX1 and TDI genes are separated by a short spacer of only 161 bp that contains numerous GC boxes and a centrally located CCAAT box embedded within a CpG island. Using luciferase as the reporter in transient transfection assays, the intergenic region was found to be a functional promoter with robust bidirectional activity. TLX1 and TDI thus appear to represent another example of a divergently transcribed gene pair whose expression is regulated by a common promoter. Our finding that TDI is transcriptionally co-activated in leukemic cells that aberrantly express TLX1, additionally suggests that it may have the potential to act as a co-operating oncogene in leukemogenesis.

Bifunctional promoter of type IV collagen COL4A5 and COL4A6 genes regulates the expression of alpha5 and alpha6 chains in a distinct cell-specific fashion

Type IV collagen is present ubiquitously in basement membranes. A bifunctional promoter regulates the expression of the alpha1/alpha2 genes, and the alpha3/alpha4 and the alpha5/alpha6 genes are also considered to be regulated by putative bifunctional promoters. Unlike the other type IV collagen chains, the alpha5(IV) and alpha6(IV) chains do not always co-localize and are present in distinct basement membranes. To address such dichotomy in the alpha5(IV) and alpha6(IV) gene regulation, we cloned a mouse genomic DNA fragment containing the promoter region between the two transcription start sites of these genes and we then placed this putative promoter sequence between the chloramphenicol acetyltransferase and Luciferase reporter genes, so that these genes would be transcribed in opposite directions in this unique construct. Glomerular endothelial cells and mesangial cells generate the kidney glomerular basement membrane, which always contains the alpha5(IV) chain but not the alpha6(IV) chain. In contrast, the basement membranes of Bowman's capsule and distal tubuli (produced by the tubular epithelial cells) contain the alpha6(IV) chain. We demonstrate that, in response to TGF-beta (transforming growth factor beta), epidermal growth factor, vascular endothelial growth factor and platelet-derived growth factor, expression from the alpha5(IV) gene is significantly enhanced in the glomerular endothelial cells and mesangial cells, but not expression from the alpha6(IV) gene. In contrast, the expression from the alpha6(IV) gene, and not that from the alpha5(IV) gene, was significantly enhanced in response to growth factors in the tubular epithelial cells. Our results demonstrate that the proximal bifunctional promoter regulates the expression of the alpha5(IV) and alpha6(IV) genes in a cell-specific manner and offers the first demonstration of the promoter plasticity in growth factor regulation of type IV collagen genes in different tissues of the body.

Genetic haploinsufficiency as a phenotypic determinant of a deletion 13q syndrome

Two cases of newborns with deletion 13q syndrome were identified and studied using electron microscopy and histologic, immunohistochemical, and special stained sections. We reviewed the published literature on genes that are haploinsufficient in the deletion 13q syndrome. The complexity of the deletion 13q syndrome phenotype is due at least in part to the haploinsufficiency of dosage-sensitive genes. Future studies need to be performed to identify their precise role in the cellular function and the development of the deletion 13q syndrome phenotype.

Anopheles gambiae collagen IV genes: cloning, phylogeny and midgut expression associated with blood feeding and Plasmodium infection

A prerequisite for understanding the role that mosquito midgut extracellular matrix molecules play in malaria parasite development is proper isolation and characterisation of the genes coding for components of the basal lamina. Here we have identified genes coding for alpha1 and alpha2 chains of collagen IV from the major malaria vector, Anopheles gambiae. Conserved sequences in the terminal NC1 domain were used to obtain partial gene sequences of this functional region, and full sequence was isolated from a pupal cDNA library. In a DNA-derived phylogeny, the alpha1 and alpha2 chains cluster with dipteran orthologs, and the alpha2 is ancestral. The expression of collagen alpha1(IV) peaked during the pupal stage of mosquito development, and was expressed continuously in the adult female following a blood meal with a further rise detected in older mosquitoes. Collagen alpha1(IV) is also upregulated when the early oocyst of Plasmodium yoelii was developing within the mosquito midgut and may contribute to a larger wound healing response. A model describing the expression of basal lamina proteins during oocyst development is presented, and we hypothesise that the development of new basal lamina between the oocyst and midgut epithelium is akin to a wound healing process.

Two overlapping divergent transcription units in the human genome: the FEN1/C11orf10 locus

Flap endonuclease 1 (FEN-1) is a nuclear enzyme involved in DNA metabolism, such as replication, repair, and recombination. Here, we report the comparative genomic organization of the chicken, mouse, and human FEN1 genes as well as the comparative organization of a small gene (C11orf10) located immediately upstream of the FEN1 gene in reverse orientation. Immunostaining revealed that the C11orf10 protein, unlike FEN-1, is located in the cytoplasm, suggesting that these two proteins do not form a physical complex. Importantly, in the human genome, the two mRNAs are overlapping (14 bp) in their 5' ends. Thus, the FEN1/C11orf10 locus is a new example of two overlapping, divergent transcription units in the human genome.

Transforming growth factor-beta signal transduction and progressive renal disease

Transforming growth factor-beta (TGF-beta) superfamily members are multifunctional growth factors that play pivotal roles in development and tissue homeostasis. Recent studies have underscored the importance of TGF-beta in regulation of cell proliferation and extracellular matrix synthesis and deposition. TGF-beta signaling is initiated by ligand binding to a membrane-associated receptor complex that has serine/threonine kinase activity. This receptor complex phosphorylates specific Smad proteins, which then transduce the ligand-activated signal to the nucleus. Smad complexes regulate target gene transcription either by directly binding DNA sequences, or by complexing with other transcription factors or co-activators. There is extensive crosstalk between the TGF-beta signaling pathway and other signaling systems, including the mitogen-activated protein kinase pathways. The importance of TGF-beta in regulation of cell growth has been emphasized by recent observations that mutations of critical elements of the TGF-beta signaling system are associated with tumor progression in patients with many different types of epithelial neoplasms. TGF-beta has emerged as a predominant mediator of extracellular matrix production and deposition in progressive renal disease and in other forms of chronic tissue injury. In this overview, recent advances in our understanding of TGF-beta signaling, cell cycle regulation by TGF-beta, and the role of TGF-beta in progressive renal injury are highlighted.

New functional roles for non-collagenous domains of basement membrane collagens

Collagens IV, XV and XVIII are major components of various basement membranes. In addition to the collagen-specific triple helix, these collagens are characterized by the presence of several non-collagenous domains. It is clear now that these ubiquitous collagen molecules are involved in more subtle and sophisticated functions than just the molecular architecture of basement membranes, particularly in the context of extracellular matrix degradation. Degradation of the basement membrane collagens occurs during numerous physiological and pathological processes such as embryonic development or tumorigenesis and generates collagen fragments. These fragments are involved in the regulation of functions differing from those of their original intact molecules. The non-collagenous C-terminal fragment NC1 of collagen IV, XV and XVIII have been recently highlighted in the literature because of their potential in reducing angiogenesis and tumorigenesis, but it is clear that their biological functions are not limited to these processes. Proteolytic release of soluble NC1 fragments stimulates migration, proliferation, apoptosis or survival of different cell types and suppresses various morphogenetic events.

Basement membrane type IV collagen molecules in the choroid plexus, pia mater and capillaries in the mouse brain

We investigated the differential distribution of basement membrane type IV collagen a chains in the mouse brain by immunohistochemistry using a chain-specific monoclonal antibodies. Subendothelial basement membranes were found to contain alpha1 and alpha2 chains. Basement membranes surrounding smooth muscle cells on blood vascular walls were immunoreactive for alpha1 and alpha2 chains but not for alpha5 and alpha6 chains. Interestingly, the pia mater contained a thin basement membrane which was positive for alpha1, alpha2, alpha5, and alpha6 chains, suggesting that glia limitans superficialis coheres basement membranes containing [alpha1(IV)]2alpha2(IV) and [alpha5(IV)]2alpha6(IV) molecules. In contrast, capillaries always possessed thin basement membranes of [alpha1(IV)]2alpha2(IV) molecules. Cerebrospinal fluid is produced through filtration of blood at the choroid plexus, where two distinct basement membranes were detected by anti-al and anti-alpha2 antibodies. The subendothelial basement membrane appeared to consist of [alpha1(IV)]2alpha2(IV) molecules, whereas the subependymal basement membrane in the choroid plexus was strongly positive for alpha3, alpha4, and alpha5 chains, indicating that the filtering unit was composed of alpha3(IV)alpha4(IV)alpha5(IV) molecules. That the specific localizations of these molecules are shared by renal glomeruli and the choroid plexus leads us to hypothesize that the supramolecular network containing alpha3(IV) alpha4(IV)alpha5(IV) molecules may function as a permeability selective barrier.

Differential distribution of basement membrane type IV collagen alpha1(IV), alpha2(IV), alpha5(IV) and alpha6(IV) chains in colorectal epithelial tumors

In this study, we examined the relationship between the histopathological grade and immunohistochemical localization of six genetically distinct type IV collagen alpha chains, the major component of basement membrane (BM), in normal and neoplastic colorectal tissues. In the normal colorectal mucosa, alpha1/alpha2(IV) and alpha5/alpha6(IV) chains were stained in all epithelial BM. However, alpha3/alpha4(IV) chains were restrictively immunostained in the BM of the apical surface epithelium. Similar immunostaining profiles for alpha1/alpha2(IV) and alpha5/alpha6(IV) chains were observed in tubular adenomas with mild/moderate atypia. However, in intramucosal carcinomas, both alpha1/alpha2(IV) chains were linearly stained in the BM of cancer cell nests, while the assembly of alpha5/alpha6(IV) chains into the BM was inhibited in a discontinuous or negatively stained pattern. The normal colorectal mucosa forms a second network of BM composed of alpha5/alpha6(IV), partly alpha3/alpha4(IV) chains, in addition to the classic network of alpha1/alpha2(IV) chains. The differential immunohistochemical localization of the type IV collagen alpha5/alpha6 chains could be one diagnostic marker for the invasiveness of colorectal cancer.

Glomerular expression of type IV collagen chains in normal and X-linked Alport syndrome kidneys

Alport syndrome is an inherited nephropathy characterized by alterations of the glomerular basement membrane because of mutations in type IV collagen genes. COL4A5 mutations, causing X-linked Alport syndrome, frequently result in the loss of the alpha5 chains of type IV collagen in basement membranes. This is associated with the absence of the alpha3(IV) and alpha4(IV) chains and increased amounts of alpha1(IV) and alpha2(IV) in glomerular basement membranes. The mechanisms resulting in such a configuration are still controversial and are of fundamental importance for understanding the pathology of the disease and for considering gene therapy. In this article we studied, for the first time, type IV collagen expression in kidneys from X-linked Alport syndrome patients, using in situ hybridization and immunohistochemistry. We show that, independent of the type of mutation and of the level of COL4A5 transcription, both COL4A3 and COL4A4 genes are actively transcribed in podocytes. Moreover, using immunofluorescence amplification, we were able to demonstrate that the alpha3 chain of type IV collagen was present in the podocytes of all patients. Finally, the alpha1(IV) chain, which accumulates within glomerular basement membranes, was found to be synthesized by mesangial/endothelial cells. These results strongly suggest that, contrary to what has been found in dogs affected with X-linked Alport syndrome, there is no transcriptional co-regulation of COL4A3, COL4A4, and COL4A5 genes in humans, and that the absence of alpha3(IV) to alpha5(IV) in glomerular basement membranes in the patients results from events downstream of transcription, RNA processing, and protein synthesis.

Absence of the alpha6(IV) chain of collagen type IV in Alport syndrome is related to a failure at the protein assembly level and does not result in diffuse leiomyomatosis

X-linked Alport syndrome is a progressive nephropathy associated with mutations in the COL4A5 gene. The kidney usually lacks the alpha3-alpha6 chains of collagen type IV, although each is coded by a separate gene. The molecular basis for this loss remains unclear. In canine X-linked hereditary nephritis, a model for X-linked Alport syndrome, a COL4A5 mutation results in reduced mRNA levels for the alpha3, alpha4, and alpha5 chains in the kidney, implying a mechanism coordinating the production of these 3 chains. To examine whether production of alpha6 chain is under the same control, we studied smooth muscle cells from this animal model. We determined the canine COL4A5 and COL4A6 genes are separated by 435 bp, with two first exons for COL4A6 separated by 978 bp. These two regions are >/= 78% identical to the human sequences that have promoter activity. Despite this potential basis for coordinated transcription of the COL4A5 and COL4A6 genes, the alpha6 mRNA level remained normal in affected male dog smooth muscle while the alpha5 mRNA level was markedly reduced. However, both alpha5 and alpha6 chains were absent at the protein level. Our results suggest that production of the alpha6 chain is under a control mechanism separate from that coordinating the alpha3-alpha5 chains and that the lack of the alpha6 chain in Alport syndrome is related to a failure at the protein assembly level, raising the possibility that the alpha5 and alpha6 chains are present in the same network. The lack of the alpha6 chain does not obviously result in disease, in particular leiomyomatosis, as is seen in Alport patients with deletions involving the COL4A5 and COL4A6 genes.

Genes for the human mitochondrial trifunctional protein alpha- and beta-subunits are divergently transcribed from a common promoter region

Human HADHA and HADHB genes encode the subunits of an enzyme complex, the trifunctional protein, involved in mitochondrial beta-oxidation of fatty acids. Both genes are located in the same region of chromosome 2p23. We isolated genomic clones, including 5' flanking regions, for HADHA and HADHB. Sequencing revealed that both of these genes are linked in a head-to-head arrangement on opposite strands and have in common a 350-bp 5' flanking region. The 5' flanking region has bidirectional promoter activity within this region; two cis elements proved critical for the activity. Transcription factor Sp1 functions as an activator for the bidirectional promoter by binding to both elements. Therefore, expression of trifunctional protein subunits are probably coordinately regulated by a common promoter and by Sp1.

Structure and mapping of the G protein gamma3 subunit gene and a divergently transcribed novel gene, gng3lg

The mammalian nervous system is rich in signaling mediated by heterotrimeric (alphabetagamma) G proteins. As an initial step to define the roles that particular gamma subunit types play in signaling, we have begun to clone and characterize those genes that encode gamma subunits enriched within neural tissue. In the present study, we have isolated and characterized the mouse gamma3 subunit gene (Gng3). The gamma3 subunit is expressed abundantly in the brain and at low levels in testes. Gng3 is composed of three exons spanning approximately 1.4 kb. A comparison of Gng3 with the gene structure for five other gamma subtypes indicates that although these proteins are diverse at the amino acid level, their exon-intron boundaries are conserved. Sequence analysis of the 5' flanking region of Gng3 revealed the presence of a novel gene, the gamma3 linked gene (Gng3lg). Gng3 and Gng3lg are organized in a head-to-head fashion with major transcription initiation sites separated by approximately 133 bp. Sequence analysis of a Gng3lg cDNA clone revealed an open reading frame encoding a 410-amino-acid protein of unknown function. Gng3lg transcripts are expressed in a variety of tissues including both brain and testes. Using an interspecific backcross panel, we localized both Gng3 and Gng3lg to the same locus on chromosome 19. The orientation, close proximity, and expression pattern of these two genes raise the distinct possibility that shared regulatory elements are used to control their expression.

Identification, distribution, and tissular origin of the alpha5(IV) and alpha6(IV) collagen chains in the developing human intestine

The basement membrane type IV collagen is a family composed of six genetically distinct but structurally similar polypeptide chains, alpha1-alpha6. The alpha1(IV) and alpha2(IV) chains are ubiquitous components of all BMs whereas the other four have a restricted tissue distribution. In the present study, we have analyzed the expression, distribution, and cellular origin of the alpha5(IV) and alpha6(IV) chains in the developing and adult human small intestine and in well-characterized in vitro models by indirect immunofluorescence, Western blot, and RT-PCR. We have found that in the fetal small intestine, alpha(IV) and alpha6(IV) are present in the epithelial BM and, in contrast to alpha1(IV) and alpha2(IV), are produced by both epithelial and mesenchymal cells. A distinct tissular origin for the alpha1/alpha2(IV) and alpha5/alpha6(IV) chains suggests that alpha5(IV) and alpha6(IV) associate as a heterotrimer in this organ. We have also found that a particular situation of alpha5(IV)/alpha6(IV) chain expression occurs in the adult intestine. Indeed, as compared with the fetal intestine, alpha6(IV) chain production is maintained while the expression of the alpha5(IV) chain is substantially reduced. Altered expression of the alpha5(IV) chain was also observed in the differentiating enterocytic-like Caco-2/15 cells, suggesting that in the intestinal model, the alpha5(IV) chain is subject to a regulated expression. Taken together, these observations indicate that the human intestinal epithelial BM contains up to four type IV collagen chains: the classical alpha1(IV)/alpha2(IV) chains, which originate from mesenchymal cells, and the alpha5(IV)/alpha6(IV) chains, which are of both epithelial and mesenchymal origin and have their expression regulated throughout development.

Alport syndrome. A review of the ocular manifestations

Alport syndrome has a prevalence of 1/5000, and 85% of patients have the X-linked form, where affected males develop renal failure and usually have a high-tone sensorineural deafness by the age of 20. The typical ocular associations are a dot-and-fleck retinopathy which occurs in about 85% of affected adult males, anterior lenticonus which occurs in about 25%, and the rare posterior polymorphous corneal dystrophy. The retinopathy and anterior lenticonus are not usually demonstrated in childhood but worsen with time so that the retinal lesion is often present at the onset of renal failure, and the anterior lenticonus, later. The demonstration of a dot-and-fleck retinopathy in any individual with a family history of Alport syndrome or with end-stage renal disease is diagnostic of Alport syndrome. The presence of anterior lenticonus or posterior polymorphous corneal dystrophy in any individual is highly suggestive of the diagnosis of Alport syndrome. Additional ocular features described in X-linked Alport syndrome include other corneal dystrophies, microcornea, arcus, iris atrophy, cataracts, spontaneous lens rupture, spherophakia, posterior lenticonus, a poor macular reflex, fluorescein angiogram hyperfluorescence, electrooculogram and electroretinogram abnormalities, and retinal pigmentation. All mutations demonstrated to date in X-linked Alport syndrome have affected the COL4A5 gene which encodes the alpha 5 chain of type IV collagen. This protein is probably common to the basement membranes of the glomerulus, cochlea, retina, lens capsule, and cornea. However, the alpha 3(IV) and 4(IV) as well as the alpha 5(IV) collagen chains are usually absent from the affected basement membranes, because the abnormal alpha 5(IV) molecule interferes with the stability of all three. The loss of these collagen molecules from the affected basement membranes results in an abnormal ultrastructural appearance. The ocular and other clinical features of autosomal recessive Alport syndrome are identical to those seen in X-linked disease, while retinopathy and cataracts are the only ocular abnormalities described in the rare autosomal dominant form of Alport syndrome. There are no ocular associations of thin basement membrane disease which is a common disease that probably represents the heterozygous expression of X-linked or autosomal recessive Alport syndrome.

The genes encoding mammalian chaperonin 60 and chaperonin 10 are linked head-to-head and share a bidirectional promoter

Chaperonins are a class of stress-inducible molecular chaperones involved in protein folding. We report the cloning, sequencing and characterisation of the rat mitochondrial chaperonin 60 and chaperonin 10 genes. The two genes are arranged in a head-to-head configuration and together comprise 14 kb and contain 14 introns. The genes are linked together by a region of approximately 280 bp, which constitutes a bidirectional promoter and includes a common heat-shock element. Insertion of the shared promoter region between two reporter genes is sufficient to drive their expression under both constitutive and heat-shock conditions. The arrangement of the mammalian chaperonin genes suggests the potential to provide the coordinated regulation of their products in a manner that is mechanistically distinct from, yet conceptually similar to, that employed by the bacterial chaperonin (groE) operon.

Structure of the rat collagen IV promoter

We have isolated a 1.6 kb clone from a rat genomic library which contains the bidirectional collagen IV promoter, flanked by exons coding for the alpha 1 (IV) and alpha 2 (IV) collagen chains. There are at least two transcription start sites within both the alpha 1 (IV) and alpha 2 (IV) collagen genes. Rat mesangial cells were transfected with chloramphenicol acetyltransferase (CAT) reporter plasmids containing segments of the promoter and 5' flanking region, in both the alpha 1 (IV) and alpha 2 (IV) orientations. Our results suggest that transcriptional efficiency of the bidirectional promoter is more efficient in the alpha 2 (IV) direction than in the alpha 1 (IV) direction.

The function of the NC1 domains in type IV collagen

At its C terminus, the collagen IV molecule bears a globular NC1 domain, to which two functions have been assigned. In the macromolecular network of collagen IV, two molecules are connected via their NC1 domains, which form a hexameric complex, stabilized by intermolecular disulfide bonds. In addition, the NC1 domains are thought to be responsible for chain selection and assembly. In order to understand the role of the NC1 domains during these steps, hexameric complexes were isolated and further investigated. SDS-polyacrylamide gel electrophoresis and Western blot revealed disulfide-linked alpha 1 (IV)NC1 and alpha 2(IV)NC1 homodimers but no heterodimers. The hexamers were dissociated at low pH, separated into monomers and dimers, and submitted to reconstitution experiments. Only alpha 1(IV)NC1 dimers were able to reconstitute a hexameric complex. alpha(IV)-NC1 and alpha 2(IV)NC1 monomers as well as the alpha 2(IV)NC1 dimers showed only a low tendency to form complexes. It is assumed that during formation of the collagen IV network, lateral aggregation of the molecules via the triple helical domains brings the C termini of two molecules into close vicinity and that subsequently the weak interactions observed between the NC1 subdomains provide the correct alignment for a disulfide exchange. It is, however, questionable whether the low affinity between the NC1 subdomains alone is sufficient for chain assembly and alignment of the alpha(IV) chains before molecule formation.

Identification and characterization of a novel transcriptional silencer in the human collagen type IV gene COL4A2

Collagen type IV [alpha 1(IV)2 alpha 2(IV)] is the basic structural component of all basement membranes. The two subunit genes COL4A1 and COL4A2 are found closely linked in the human and murine genomes and are transcribed divergently from a common promoter. Previously, activating elements had been detected within both genes which are indispensable for efficient transcription. An additional negative regulatory element has now been identified within the third intron of the COL4A2 gene which is able to inhibit transcription of both COL4 genes from their shared promoter, as well as the nonrelated herpes simplex virus thymidine kinase promoter. The element exerts its inhibitory effect largely independently from its relative orientation and distance from the initiation site of transcription. Therefore, the element represents a silencer which is named the "COL4 silencer." The minimal functional silencer could be narrowed down by deletion mapping to a sequence element located within intron 3 of the COL4A2 gene. This motif is specifically recognized by a nuclear protein, named "SILBF," and the binding site of which was determined by footprinting assays. Mutation studies and deletion analysis proved that the presence of this sequence element and its interaction with SILBF is not only essential but also sufficient for the silencing function. We assume that the COL4 silencer plays an important role in the control of overall expression and the balance of divergent transcription of both COL4 genes.

Homologs of genes and anonymous loci on human chromosome 13 map to mouse chromosomes 8 and 14

To enhance the comparative map for human Chromosome (Chr) 13, we identified clones for human genes and anonymous loci that cross-hybridized with their mouse homologs and then used linkage crosses for mapping. Of the clones for four genes and twelve anonymous loci tested, cross-hybridization was found for six, COL4A1, COL4A2, D13S26, D13S35, F10, and PCCA. Strong evidence for homology was found for COL4A1, COL4A2, D13S26, D13S35, and F10, but only circumstantial homology evidence was obtained for PCCA. To genetically map these mouse homologs (Cf10, Col4a1, Col4a2, D14H13S26, D8H13S35, and Pcca-rs), we used interspecific and intersubspecific mapping panels. D14H13S26 and Pcca-rs were located on the distal portion of mouse Chr 14 extending by approximately 30 cM the conserved linkage between human Chr 13 and mouse Chr 14, assuming that Pcca-rs is the mouse homolog of PCCA. By contrast, Cf10, Col4a1, Col4a2, and D8H13S35 mapped near the centromere of mouse Chr 8, defining a new conserved linkage. Finally, we identified either a closely linked sequence related to Col4a2, or a recombination hot-spot between Col4a1 and Col4a2 that has been conserved in humans and mice.

Analysis of the chicken GPAT/AIRC bidirectional promoter for de novo purine nucleotide synthesis

GPAT and AIRC encode two enzymes that catalyze steps 1 and 6 plus 7, respectively, of the de novo purine biosynthetic pathway. The chicken genes are closely linked and divergently transcribed from an approximately 230-base pair intergenic region. The promoter was scanned by deletion mutagenesis in a bireporter vector that allowed assay of transcriptional activity in both directions in transfected HepG2 and chicken LMH cells. Three classes of deletions were obtained: those affecting bidirectional transcription, those predominantly affecting GPAT transcription, and those predominantly affecting AIRC transcription. Defects in bidirectional transcription resulted from removal of an initiator-like element overlapping the AIRC transcription start site, as well as deletions removing a series of GC and CCAAT boxes from the AIRC proximal half of the promoter and a CCAAT-containing segment from the GPAT side. Several regions in the GPAT proximal half of the promoter, including an octamer-like motif downstream from the transcription start site, were required predominantly for GPAT expression. Evidence for interaction of HeLa nuclear proteins with some of these sites was obtained by gel retardation, DNase I, and methylation interference assays. Overall, the results showed that the intergenic region is an integrated bidirectional promoter and that a novel initiator-like element plays a central role in coordinating expression of the divergently transcribed AIRC and GPAT genes.

Sequencing and promoter analysis of the genomic region between the rat neuronal nicotinic acetylcholine receptor beta 4 and alpha 3 genes

Nicotinic acetylcholine receptors (nAChRs) found on neurons are composed of ligand binding (alpha) and structural (beta) subunits. Different combinations of alpha and beta subunits produce nAChR subtypes with different pharmacological and ion-conducting properties. Transcriptional regulation may be an important determinant of receptor subtype in a neuronal population and thus influence transmission through a ganglion or group of neurons in the CNS by controlling the nAChR subtype(s) present. In order to understand the transcriptional regulation of neuronal nAChRs by cell contact and electrical activity, it will be first necessary to identify DNA elements that control the expression of members of this family and to identify factors required for the expression of these genes. In this report we have begun to examine the 5'-flanking region of one member of the nAChR family of genes, alpha 3. We have sequenced the region between the beta 4 and alpha 3 genes and have identified two promoter regions in the beta 4-alpha 3 intergenic region. One region is close to the beta 4 gene downstream of exon 6 and has strong promoter activity in both orientations; the other is close to the start of the alpha 3 gene coding region. A region with putative silencer activity is also found near the upstream promoter. This bidirectional promoter region could be involved in the control of alpha 3 and beta 4 gene expression.

Exclusion of eight genes as mutated loci in congenital nephrotic syndrome of the Finnish type

The congenital nephrotic syndrome of the Finnish type (CNF) is an autosomal recessive disease characterized by massive proteinuria already at birth. The gene locus defective in CNF was searched for using polymorphic markers of candidate genes coding for components of the basement membrane (BM). The linkage analyses in 17 Finnish CNF families demonstrated exclusion of obligatory recombination events between the disease and eight genes coding for BM components. The genes coding for the alpha 1(IV), alpha 2(IV), alpha 3(IV) and alpha 4(IV) chain of type IV collagen, the B1e, B2e and B2t chains of laminin, as well as the BM heparan sulfate proteoglycan core protein were all excluded in this Finnish family material. Since the defect is not in any of the genes coding for major components of BM, the identification of the gene defect will most probably reveal a new gene important for the development and function of the glomerular basement membrane.