The role of Fras1/Frem proteins in the structure and function of basement membrane.
ABSTRACT Basement membranes constitute architecturally complex extracellular matrix (ECM) protein networks of great structural and regulatory importance. Recently, a novel group of basement membrane proteins, Fras1 (Fraser syndrome protein (1) and the Fras1-related extracellular matrix proteins Frem1, Frem2 and Frem3, has emerged. They comprise components of the sublamina densa region and contribute to embryonic epithelial-mesenchymal integrity. Fras1/Frem share common polypeptide repetitive motifs with possible interactive and organizing functions. Mutations in genes encoding Fras1, Frem1 and Frem2 are causative for dermal-epidermal detachment in the plane of sublamina densa and have been identified in different classes of mouse bleb mutants, the murine model of human Fraser syndrome, the hallmark phenotypic characteristics of which are embryonic skin blistering, cryptophthalmos and renal agenesis. Indeed, defects in FRAS1 and FREM2 have been identified in Fraser syndrome patients. The phenotypic similarity of mouse bleb mutant strains can be attributed to the fact that Fras1, Frem1 and Frem2 have been experimentally shown to interact, forming a mutually stabilized protein complex, while Frem3, which has not yet been associated with any of the existing known mutations, operates in a more independent fashion. Fras1/Frem have been recently proposed to compensate for the activity of collagen VII, a major anchoring component of the sublamina densa, the levels of which rise only during late embryonic life. By focusing on the aforementioned data, in this review we will summarize the current knowledge about Fraser syndrome proteins and describe their contribution to basement membrane biology.
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ABSTRACT: Manitoba Oculotrichoanal (MOTA) syndrome is an autosomal recessive disorder present in First Nations families that is characterized by ocular (cryptophthalmos), facial, and genital anomalies. At the commencement of this study, its genetic basis was undefined. Homozygosity analysis was employed to map the causative locus using DNA samples from four probands of Cree ancestry. After single nucleotide polymorphism (SNP) genotyping, data were analyzed and exported to PLINK to identify regions identical by descent (IBD) and common to the probands. Candidate genes within and adjacent to the IBD interval were sequenced to identify pathogenic variants, with analyses of potential deletions or duplications undertaken using the B-allele frequency and log(2) ratio of SNP signal intensity. Although no shared IBD region >1 Mb was evident on preliminary analysis, adjusting the criteria to permit the detection of smaller homozygous IBD regions revealed one 330 Kb segment on chromosome 9p22.3 present in all 4 probands. This interval comprising 152 SNPs, lies 16 Kb downstream of FRAS1-related extracellular matrix protein 1 (FREM1), and no copy number variations were detected either in the IBD region or FREM1. Subsequent sequencing of both genes in the IBD region, followed by FREM1, did not reveal any mutations. This study illustrates the utility of studying geographically isolated populations to identify genomic regions responsible for disease through analysis of small numbers of affected individuals. The location of the IBD region 16 kb from FREM1 suggests the phenotype in these patients is attributable to a variant outside of FREM1, potentially in a regulatory element, whose identification may prove tractable to next generation sequencing. In the context of recent identification of FREM1 coding mutations in a proportion of MOTA cases, characterization of such additional variants offers scope both to enhance understanding of FREM1's role in cranio-facial biology and may facilitate genetic counselling in populations with high prevalences of MOTA to reduce the incidence of this disorder.Molecular vision 01/2012; 18:1301-11. · 2.20 Impact Factor
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ABSTRACT: Fraser syndrome (FS) features renal agenesis and cystic kidneys. Mutations of FRAS1 (Fraser syndrome 1)and FREM2 (FRAS1-related extracellular matrix protein 2)cause FS. They code for basement membrane proteins expressed in metanephric epithelia where they mediate epithelial/mesenchymal signalling. Little is known about whether and where these molecules are expressed in more mature kidneys. In healthy and congenital polycystic kidney (cpk)mouse kidneys we sought Frem2 expression using a LacZ reporter gene and quantified Fras family transcripts. Fras1 immunohistochemistry was undertaken in cystic kidneys from cpk mice and PCK (Pkhd1 mutant) rats (models of autosomal recessive polycystic kidney disease) and in wildtype metanephroi rendered cystic by dexamethasone. Nascent nephrons transiently expressed Frem2 in both tubule and podocyte epithelia. Maturing and adult collecting ducts also expressed Frem2. Frem2 was expressed in cpk cystic epithelia although Frem2 haploinsufficiency did not significantly modify cystogenesis in vivo. Fras1 transcripts were significantly upregulated, and Frem3 downregulated, in polycystic kidneys versus the non-cystic kidneys of littermates. Fras1 was immunodetected in cpk, PCK and dexamethasone-induced cystepithelia. These descriptive results are consistent with the hypothesis that Fras family molecules play diverse roles in kidney epithelia. In future, this should be tested by conditional deletion of FS genes in nephron segments and collecting ducts.Pediatric Nephrology 10/2011; 27(6):991-8. · 2.52 Impact Factor