An integrated genetic map of the pearl locus of mouse chromosome 13

Analysis of the human integrin alpha11 gene (ITGA11) and its promoter

Integrin alpha11beta1 is a collagen receptor which is expressed in a subset of mesenchymally-derived tissues during embryogenesis. Based on available human chromosome 15-derived sequences and genomic PCR, the complete exon structure of ITGA11, including the proximal promoter, was assembled into 30 exons. The inserted region (encoding amino acids 804-826) distinguishing alpha11 from other integrin alpha chains, was placed in the very beginning of exon 20. PCR data failed to show alternative splicing of RNA transcribed from this region. Using the oligo-capping technique a major transcription start site was mapped 30 nucleotides upstream of the translation start and identified as an abbreviated initiator sequence. Promoter sequence analysis in silico suggested the presence of multiple binding sites for transcription factors in the region upstream of the transcription start. 3 kb of the 5' flanking sequence was isolated and used to generate luciferase promoter constructs. In the fibrosarcoma cell line HT1080 a core promoter [nt (-)127-(+)25], a potential silencer region [nt (-)400-(-)127] and a potential enhancer region [nt (-)1519-(-)400], were identified as being important for alpha11 transcription in mesenchymal cells. Furthermore, studies of the promoter region will provide valuable information regarding the molecular mechanisms underlying the cell- and tissue- specific expression pattern of ITGA11.

cDNA cloning and chromosomal localization of human alpha(11) integrin. A collagen-binding, I domain-containing, beta(1)-associated integrin alpha-chain present in muscle tissues

We previously identified a novel integrin alpha-chain in human fetal muscle cells (Gullberg, D., Velling, T., Sjöberg, G., and Sejersen, T. (1995) Dev. Dyn. 204, 57-65). We have now isolated the full-length cDNA for this integrin subunit, alpha(11). The open reading frame of the cDNA encodes a precursor of 1188 amino acids. The predicted mature protein of 1166 amino acids contains seven conserved FG-GAP repeats, an I domain with a metal ion-dependent adhesion site motif, a short transmembrane region, and a unique cytoplasmic domain of 24 amino acids containing the sequence GFFRS. alpha(11), like other I domain integrins, lacks a dibasic cleavage site for generation of a heavy chain and a light chain, and it contains three potential divalent cation binding sites in repeats 5-7. The presence of 22 inserted amino acids in the extracellular stalk portion (amino acids 804-826) distinguishes the alpha(11) integrin sequence from other integrin alpha-chains. Amino acid sequence comparisons reveal the highest identity of 42% with the alpha(10) integrin chain. Immunoprecipitation with antibodies to alpha(11) integrin captures a 145-kDa protein distinctly larger than the 140-kDa alpha(2) integrin chain when analyzed by SDS-polyacrylamide gel electrophoresis under nonreducing conditions. Fluorescence in situ hybridization maps the integrin alpha(11) gene to chromosome 15q23, in the vicinity of an identified locus for Bardet-Biedl syndrome. Based on Northern blotting, integrin alpha(11) mRNA levels are high in the adult human uterus and in the heart and intermediate in skeletal muscle and some other tissues tested. During in vitro myogenic differentiation, alpha(11) mRNA and protein are up-regulated. Studies of ligand binding properties show that alpha(11)beta(1) binds collagen type I-Sepharose, and cultured muscle cells localize alpha(11)beta(1) into focal contacts on collagen type I. Future studies will reveal the importance of alpha(11)beta(1) for muscle development and integrity in adult muscle and other tissues.

Abnormal Expression and Subcellular Distribution of Subunit Proteins of the AP-3 Adaptor Complex Lead to Platelet Storage Pool Deficiency in the Pearl Mouse

The pearl mouse is a model for Hermansky Pudlak Syndrome (HPS), whose symptoms include hypopigmentation, lysosomal abnormalities, and prolonged bleeding due to platelet storage pool deficiency (SPD). The gene for pearl has recently been identified as the beta3A subunit of the AP-3 adaptor complex. The objective of these experiments was to determine if the expression and subcellular distribution of the AP-3 complex were altered in pearl platelets and other tissues. The beta3A subunit was undetectable in all pearl cells and tissues. Also, expression of other subunit proteins of the AP-3 complex was decreased. The subcellular distribution of the remaining AP-3 subunits in platelets, macrophages, and a melanocyte-derived cell line of pearl mice was changed from the normal punctate, probably endosomal, pattern to a diffuse cytoplasmic pattern. Ultrastructural abnormalities in mutant lysosomes were likewise apparent in mutant kidney and a cultured mutant cell line. Genetically distinct mouse HPS models had normal expression of AP-3 subunits. These and related experiments strongly suggest that the AP-3 complex regulates the biogenesis/function of organelles of platelets and other cells and that abrogation of expression of the AP-3 complex leads to platelet SPD.

A radiation hybrid map of mouse chromosome 13

A mouse radiation hybrid (RH) panel was used to make a framework map for the entire length of mouse chromosome (Chr) 13. Forty-one loci were typed, and while most used primers flanking simple sequence repeats, some genes were included. The most proximal and distal loci are D13Mit132 and D13Mit35. The estimate of map length for Chr 13 is 1328 cR. The map is compared with the same set of loci from the consensus map for Chr 13, which is 70 cM in length, and also with a recombinational map derived from an intraspecies cross typed for many of the same loci. The mouse RH panel gave good resolution for Chr 13 and at the distal end allowed separation of previously nonrecombinant markers that are present on a single 620-kb YAC clone. Data analysis was performed using the RH option for Map Manager QT. This framework RH map of Chr 13 is the second of a series of RH maps for mouse chromosomes.

The Cspg2 gene, disrupted in the hdf mutant, is required for right cardiac chamber and endocardial cushion formation

The heart defect (hdf) mouse is a recessive lethal that arose from a transgene insertional mutation on chromosome 13. Embryos homozygous for the transgene die in utero by embryonic day 10.5 postcoitus and exhibit specific defects along the anterior-posterior cardiac axis. The future right ventricle and conus/truncus of the single heart tube fail to form and the endocardial cushions in the atrioventricular and conus/truncus regions are absent. Because the hdf mouse mutation provided the opportunity to identify a gene required for endocardial cushion formation and for specification or maintenance of the anterior most segments of the heart, we initiated studies to further characterize the phenotype, clone the insertion site, and identify the gene disrupted. Chromosome mapping studies first identified the gene, Cspg2 (versican), as a candidate hdf gene. In addition, an antibody recognizing a glycosaminoglycan epitope on versican was found to be positive by immunohistochemistry in the extracellular matrix of normal wild-type embryonic hearts, but absent in homozygous hearts. Expression analysis of the Cspg2 gene showed that the 6/8, 6/9, and 7/9 Cspg2 exon boundaries were present in mRNA of normal wild-type embryonic hearts but absent in the homozygous mutant embryos. DNA sequence flanking the transgene was used to isolate from a normal mouse library overlapping genomic DNA segments that span the transgene insertion site. The contiguous genomic DNA segment was found to contain exon 7 of the Cspg2 in a position 3' to the transgene insertion site. These four separate lines of evidence support the hypothesis that Cspg2 is the gene disrupted by the transgene insertion in the hdf mouse line. The findings of this study and our previous studies of the hdf insertional mutant mouse have shown that normal expression of the Cspg2 gene is required for the successful development of the endocardial cushion swellings and the embryonic heart segments that give rise to the right ventricle and conus/truncus in the outlet of the looped heart.

Mouse models of Hermansky Pudlak syndrome: a review

Hermansky Pudlak Syndrome (HPS) is a recessively inherited disease affecting the contents and/or the secretion of several related subcellular organelles including melanosomes, lysosomes, and platelet dense granules. It presents with disorders of pigmentation, prolonged bleeding, and ceroid deposition, often accompanied by severe fibrotic lung disease and colitis. In the mouse, the disorder is clearly multigenic, caused by at least 14 distinct mutations. Studies on the mouse mutants have defined the granule abnormalities of HPS and have shown that the disease is associated with a surprising variety of phenotypes affecting many tissues. This is an exciting time in HPS research because of the recent molecular identification of the gene causing a major form of human HPS and the expected identifications of several mouse HPS genes. Identifications of mouse HPS genes are expected to increase our understanding of intracellular vesicle trafficking, lead to discovery of new human HPS genes, and suggest diagnostic and therapeutic approaches toward the more severe clinical consequences of the disease.

rim2 (recombination-induced mutation 2) is a new allele of pearl and a mouse model of human Hermansky-Pudlak syndrome (HPS): genetic and physical mapping

A mouse mutation, rim2, is one of a series of spontaneous mutations that arose from the intra-MHC recombinants between Japanese wild mouse-derived wm7 and laboratory MHC haplotypes. This mutation is single recessive and characterized by diluted coat color and hypo-pigmentation of the eyes. We mapped the rim2 gene close to an old coat color mutation, pearl (pe), on Chromosome (Chr) 13 by the high-density linkage analysis. The pearl mutant is known to have abnormalities similar to Hermansky-Pudlak syndrome (HPS), a human hemorrhagic disorder, characterized by albinism and storage pool deficiency (SPD) of dense granules in platelets. A mating cross of C57BL10/Slc-rim2/rim2 and C57BL/6J-pe/pe showed no complementation of coat color. Additionally, characteristics similar to SPD were also observed in rim2. Thus, rim2 appeared to be a new allele of the pe locus and serves as a mouse model for human HPS. We have made a YAC contig covering the rim2/pe locus toward positional cloning of the causative gene.