Distinct biochemical characteristics of the two human profilin isoforms

The biochemical characteristics of a new human profilin isoform are described. We refer to this recently described isoform as profilin II (isoelectric point 5.9) in comparison to profilin I (pI 8.4). We expressed both isoforms in bacteria and compared their actin-binding properties, binding to poly(L-proline), affinities for phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2], and their effects on nucleotide exchange on actin. Profilin I and profilin II have similar affinities for PtdIns(4,5)P2 and poly(L-proline), and both accelerate nucleotide exchange on monomeric actin to the same extent. However, the affinity of profilin I for monomeric actin is about five times higher than the affinity of profilin II for actin. Potential structural differences of profilin I and profilin II that might explain the difference in actin binding are discussed.

Hemostatic, inflammatory, and fibroblast responses are blunted in mice lacking gelsolin

Gelsolin, an 82 kDa actin-binding protein, has potent actin filament-severing activity in vitro. To investigate the in vivo function of gelsolin, transgenic gelsolin-null (Gsn-) mice were generated and found to have normal embryonic development and longevity. However, platelet shape changes are decreased in Gsn- mice, causing prolonged bleeding times. Neutrophil migration in vivo into peritoneal exudates and in vitro is delayed. Gsn- dermal fibroblasts have excessive actin stress fibers and migrate more slowly than wild-type fibroblasts, but have increased contractility in vitro. These observations establish the requirement of gelsolin for rapid motile responses in cell types involved in stress responses such as hemostasis, inflammation, and wound healing. Neither gelsolin nor other proteins with similar actin filament-severing activity are expressed in early embryonic cells, indicating that this mechanism of actin filament dynamics is not essential for motility during early embryogenesis.

Clinical, neuropathological and genetic aspects of the tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is an autosomal dominant syndrome in which patients develop hamartomatous lesions in the nervous system and a host of other organs. While considerable experience has been gained in defining the clinical spectrum of TSC, a number of nosological questions remain. Neuropathological studies have continued to refine our knowledge of the nervous system abnormalities that characterize TSC. Molecular genetic studies have implicated two chromosomal regions in the genesis of TSC, one on chromosome 9q and the other on chromosome 16p. The chromosome 16p gene, designated TSC2, has been cloned, although its function remains speculative. The identification of the TSC1 gene on chromosome 9q, along with functional studies and mutational analyses of both TSC genes, will likely provide fascinating insights into the pathogenesis of TSC.

COL5A1: fine genetic mapping and exclusion as candidate gene in families with nail-patella syndrome, tuberous sclerosis 1, hereditary hemorrhagic telangiectasia, and Ehlers-Danlos Syndrome type II

COL5A1, the gene for the alpha 1 chain of type V collagen, has been considered a candidate gene for certain diseases based on chromosomal location and/or disease phenotype. We have employed 3'-untranslated region RFLPs to exclude COL5A1 as a candidate gene in families with tuberous sclerosis 1, Ehlers-Danlos syndrome type II, and nail-patella syndrome. In addition, we describe a polymorphic simple sequence repeat (SSR) within a COL5A1 intron. This SSR is used to exclude COL5A1 as a candidate gene in hereditary hemorrhagic telangiectasia (Osler-Rendu-Weber disease) and to add COL5A1 to the existing map of "index" markers of chromosome 9 by evaluation of the COL5A1 locus on the CEPH 40-family reference pedigree set. This genetic mapping places COL5A1 between markers D9S66 and D9S67.

Identification of VAV2 on 9q34 and its exclusion as the tuberous sclerosis gene TSC1

A novel widely expressed homologue of the VAV oncogene, VAV2 (53% identical residues), has been identified within the critical region for the tuberous sclerosis gene, TSC1, on human chromosome 9q34. By Southern blot analysis, analysis of allele-specific transcription, and direct sequencing of the VAV2 mRNA/cDNA from patient lymphoblastoid cell lines, we demonstrate that both alleles of this gene are expressed in TSC patients and there are no significant mutations. VAV consists of a novel array of signalling domains and is thought to play an important role in signal transduction in haematopoietic tissues where it is exclusively expressed. VAV2 is likely to serve a similar role more generally in mammalian cells, but is not the TSC1 gene.

The human actin-regulatory protein cap G: gene structure and chromosome location

Cap G (formerly called macrophage capping protein or gCap39) is a member of the gelsolin/villin family of actin-regulatory proteins. Unlike all other members of this family, Cap G caps the barbed ends of actin filaments, but does not sever them. This protein is half the molecular weight and contains half the number of repeat subunits (3 vs 6) of gelsolin and villin, suggesting that these two proteins may have arisen by gene duplication of the Cap G gene. To investigate this possibility we have cloned and sequenced the human Cap G gene (gene symbol CAPG). The gene is 16.6 kb in size, contains 10 exons and 9 introns, and is located on the proximal short arm of chromosome 2. The open reading frame is 6.9 kb, having 9 exons and 8 introns. This region contains 3 splice sites that are nearly identical to the human gelsolin gene, but shares only one with villin, indicating that CAPG is more closely related to gelsolin. Further comparisons of these three genes, however, indicate that the evolutionary steps resulting in human gelsolin and villin are likely to have been more complex than a simple tandem duplication of the Cap G gene.

Tuberous sclerosis

BACKGROUND AND DESIGN

Tuberous sclerosis (TS) is a genetic disease with prominent cutaneous and brain involvement whose clinical and molecular genetics are reviewed.

OBSERVATIONS

Tuberous sclerosis is a systemic disorder (incidence one in 10,000) characterized by benign growths (hamartias and hamartomas) in multiple organ systems. Involvement of the brain can result in persistent seizures and mental retardation; skin involvement includes facial angiofibromas, subungual fibromas, hypomelanotic macules, forehead fibrous plaques, and Shagreen's patches. Approximately 60% of TS occurs as apparent sporadic cases. In families, it has autosomal dominant inheritance with high penetrance (approximately 95%), with careful clinical and radiologic evaluation. Genetic linkage analysis indicates that about half of all TS families show linkage to chromosome 9q34, and about half to chromosome 16p13. There are no distinguishing features in the two groups of families showing linkage to the two genomic regions, nor strong evidence for a third causative gene. Positional cloning efforts for both chromosomal regions have limited the region containing the gene to about 1 to 2 million bases.

CONCLUSIONS

Identification of the two TS genes should illuminate the pathogenesis of TS and provide opportunities for genetic counseling, prenatal diagnosis, and therapeutic intervention.

An index marker map of chromosome 9 provides strong evidence for positive interference

An index marker map of chromosome 9 has been constructed using the Centre d'Etude du Polymorphisme Humain reference pedigrees. The map comprises 26 markers, with a maximum intermarker interval of 13.1 cM and only two intervals > 10 cM. Placement of all but one marker into the map was achieved with > 10,000:1 odds. The sex-equal length is 151 cM, with male length of 121 cM and female length of 185 cM. The map extends to within 2%-3% of physical length at the telomeres, and its coverage therefore is expected to be within 20-30 cM of full map length. The markers are all of the GT/CA repeat type and have average heterozygosity .77, with a range of .60-.89. The map shows both marked contraction of genetic distance relative to physical distance in the pericentromeric region and expansion in the telomeric regions. Genotypic data were carefully examined for errors by using the crossover routine of the program DATAMAN. Five new mutations were observed among 17,316 meiotic events examined. There were two double-crossover events occurring within an interval of 0-10 cM, and another eight were observed within an interval of 10-20 cM. Many of these could be due to additional mutational events in which one parental allele converted to the other by either gene conversion or random strand slippage. When there was no correction for these possible mutational events, the number of crossovers displayed by the maternal and paternal chromosomes was significantly different (P < .001) from that predicted by the Poisson distribution, which would be expected in the absence of interference. In addition, the observed crossover distribution for paternally derived chromosomes was similar to that predicted from cytogenetic chiasma frequency observations. In all, the data strongly support the occurrence of strong positive interference on human chromosome 9 and suggest that flanking markers at an interval of < or = 20 cM are generally sufficient for disease gene inheritance predictions in presymptomatic genetic counseling by linkage analysis.

A high-resolution linkage map of human 9q34.1

A map comprising 16 distinct markers with heterozygosities of 0.61-0.92 for a 10-cM region of human 9q34.1 is presented. The map incorporates four genes and has a maximum intermarker interval of 2.1 cM. Markers were analyzed in the Venezuelan reference pedigrees and all were placed uniquely in the map with a minimum likelihood of 676:1. The map should prove useful in analysis of families segregating dystonia and tuberous sclerosis, as the DYT1 and TSC1 loci map within this region.

Actin-binding protein (ABP-280) filamin gene (FLN) maps telomeric to the color vision locus (R/GCP) and centromeric to G6PD in Xq28

Actin-binding protein-280 (ABP-280) is a dimeric actin filament crosslinking protein that promotes orthogonal branching of actin filaments and links actin filaments to membrane glycoproteins. We have mapped the ABP-280 filamin gene (FLN) to Xq28 by Southern blot analysis of somatic cell hybrid lines, by fluorescence in situ hybridization, and through identification of portions of the FLN gene within cosmids and YACs mapped to Xq28. The FLN gene is found within a 200-kb region centromeric to the G6PD locus and telomeric to DSX52 and the color vision locus.

Identification of markers flanking the tuberous sclerosis locus on chromosome 9 (TSC1)

Analysis of a large tuberous sclerosis pedigree confirmed linkage to a locus on the long arm of chromosome 9, with recombination events placing the disease gene distal to gelsolin and proximal to dopamine beta-hydroxylase.

Suppression of tumorigenicity in simian virus 40-transformed 3T3 cells transfected with alpha-actinin cDNA

Human cytoskeletal alpha-actinin cDNA was transfected into highly malignant simian virus 40-transformed BALB/c 3T3 (SVT2) cells that express 6-fold lower levels of alpha-actinin than nontransformed BALB/c 3T3 cells. SVT2 clones expressing various levels of alpha-actinin were isolated and their structure and tumorigenic properties were determined. Transfected SVT2 clones expressing alpha-actinin at levels found in nontumorigenic 3T3 cells displayed a flatter phenotype, a decreased ability to grow in suspension culture in soft agar, and a marked reduction in their ability to form tumors in syngeneic BALB/c mice and in athymic nude mice. Clones overexpressing alpha-actinin at the highest level (about 2-fold higher than 3T3 cells) were completely suppressed in their ability to form tumors in syngeneic BALB/c mice. The results suggest that alpha-actinin, an actin-crosslinking protein that is also localized in cell junctions, may have an effective suppressive ability on the transformed phenotype.

A genetic linkage map of human chromosome 9q

A genetic linkage map of human chromosome 9q, spanning a sex-equal distance of 125 cM, has been developed by genotyping 26 loci in the Venezuelan Reference Pedigree. The loci include 12 anonymous microsatellite markers reported by Kwiatkowski et al. (1992), several classical systems previously assigned to chromosome 9q, and polymorphisms for the genes tenacin (HXB), gelsolin (GSN), adenylate kinase 1 (AK1), arginosuccinate synthetase (ASS), ABL oncogene (ABL1), ABO blood group (ABO), and dopamine beta-hydroxylase (DBH). Only a marginally significant sex difference is found along the entire length of the map and results from one interval, between D9S58 and D9S59, that displays an excess of female recombination. A comparison of the genetic map to the existing physical data suggests that there is increased recombination in the 9q34 region with a recombination event occurring every 125-400 kb. This map should be useful in further characterizing the relationship between physical distance and genetic distance, as well as for genetic linkage studies of diseases that map to chromosome 9q, including multiple self-healing squamous epithelioma (MSSE), Gorlin syndrome (NBCCS), xeroderma pigmentosum (XPA), nail-patella syndrome (NPS1), torsion dystonia (DYT1), and tuberous sclerosis (TSC1).

Evidence for genetic heterogeneity in tuberous sclerosis: one locus on chromosome 9 and at least one locus elsewhere

Linkage of tuberous sclerosis complex (TSC), an autosomal dominant disorder, to markers on chromosome 9 was reported first in 1987. This assignment was confirmed by an international collaborative study that suggested more than one locus may be responsible for the phenotype. We studied 14 multigenerational TSC families (13 previously unreported) with markers for nine loci in the linked region of chromosome 9q32-q34. Our results confirm the previous reports that the genetic locus in one-third to one-half of families maps to chromosome 9. Comparison of clinical findings in the chromosome 9-linked families with those in the chromosome 9-unlinked families reveals only a higher incidence of ungual fibromata in the chromosome 9-linked families.

Exclusion of the gelsolin gene on 9q32-34 as the cause of familial lattice corneal dystrophy type I

Familial lattice corneal dystrophy type I (LCD1) is a localized form of inherited amyloidosis limited to the corneal stroma. Recently the Finnish form of hereditary amyloidosis with lattice corneal dystrophy has been shown to be due to a mutation in the gelsolin gene (G654----A; Asp187----Asn). In this paper we exclude the gelsolin gene as the cause of the autosomal dominant form of isolated LCD1.

A radiation-reduced hybrid cell line containing 5 Mb/17 cM of human DNA from 9q34

Disease gene loci for tuberous sclerosis (TSC1), idiopathic torsion dystonia (DYT1), and nail-patella syndrome (NPS1) have been mapped by genetic linkage analysis to human chromosome 9q band 34. To create a resource for physical mapping and manipulation of this region of the genome, we have created a radiation-reduced hybrid cell line containing DNA from human 9q34 as its only human component. This cell line, E6B, has been characterized by Southern blot and PCR analysis using a panel of 9q markers and fluorescent in situ hybridization. We estimate that it contains 5 Mb of human DNA, equal to 17 cM of genetic distance, extending from AK1 to ABO on 9q34.

In vivo analysis of functional domains from villin and gelsolin

Transfected CV1 cells were used to compare the in vivo effects of various domains of villin and gelsolin. These two homologous actin modulating proteins both contain a duplicated severin-like sequence. Villin has in addition a carboxy-terminal domain, the headpiece, which accounts for its bundling activity. The effects of the villin-deleted mutants were compared with those of native villin. Our results show that essential domains of villin required to induce the growth of microvilli and F-actin redistribution are present in the first half of the core and in the headpiece. We also show that the second half of the villin core cannot be exchanged by its homolog in gelsolin. When expressed at high levels of CV1 cells, full length gelsolin completely disrupted stress fibers without change of the cell shape. Addition of the villin headpiece to gelsolin had no effect on the phenotype induced by gelsolin alone. Expression of the first half of gelsolin induced similar modifications as capping proteins and rapid cell mortality; this deleterious effect on the cell structure was also observed when the headpiece was linked to the first half of gelsolin. In cells expressing the second half of gelsolin, a dotted F-actin staining was often seen. Moreover elongated dorsal F-actin structures were observed when the headpiece was linked to the second gelsolin domain. These studies illustrate the patent in vivo severing activity of gelsolin as well as the distinct functional properties of villin core in contrast to gelsolin.

Strong allelic association between the torsion dystonia gene (DYT1) andloci on chromosome 9q34 in Ashkenazi Jews

The DYT1 gene responsible for early-onset, idiopathic torsion dystonia (ITD) in the Ashkenazi Jewish population, as well as in one large non-Jewish family, has been mapped to chromosome 9q32-34. Using (GT)n and RFLP markers in this region, we have identified obligate recombination events in some of these Jewish families, which further delineate the area containing the DYT1 gene to a 6-cM region bounded by loci AK1 and ASS. In 52 unrelated, affected Ashkenazi Jewish individuals, we have found highly significant linkage disequilibrium between a particular extended haplotype at the ABL-ASS loci and the DYT1 gene. The 4/A12 haplotype for ABL-ASS is present on 69% of the disease-bearing chromosomes among affected Jewish individuals and on only 1% of control Jewish chromosomes (chi 2 = 91.07, P much less than .001). The allelic association between this extended haplotype and DYT1 predicts that these three genes lie within 1-2 cM of each other; on the basis of obligate recombination events, the DYT1 gene is centromeric to ASS. Furthermore, this allelic association supports the idea that a single mutation event is responsible for most hereditary cases of dystonia in the Jewish population. Of the 53 definitely affected typed, 13 appear to be sporadic, with no family history of dystonia. However, the proportion of sporadic cases which potentially carry the A12 haplotype at ASS (8/13 [62%]) is similar to the proportion of familial cases with A12 (28/40 [70%]). This suggests that many sporadic cases are hereditary, that the disease gene frequency is greater than 1/15,000, and that the penetrance is lower than 30%, as previously estimated in this population. Most affected individuals were heterozygous for the ABL-ASS haplotype, a finding supporting autosomal dominant inheritance of the DYT1 gene. The ABL-ASS extended-haplotype status will provide predictive value for carrier status in Jewish individuals. This information can be used for molecular diagnosis, evaluation of subclinical expression of the disease, and elucidation of environmental factors which may modify clinical symptoms.