Faciogenital dysplasia protein (FGD1) and Vav, two related proteins required for normal embryonic development, are upstream regulators of Rho GTPases.

BACKGROUND: Dbl, a guanine nucleotide exchange factor (GEF) for members of the Rho family of small GTPases, is the prototype of a family of 15 related proteins. The majority of proteins that contain a DH (Dbl homology) domain were isolated as oncogenes in transfection assays, but two members of the DH family, FGD1 (the product of the faciogenital dysplasia or Aarskog-Scott syndrome locus) and Vav, have been shown to be essential for normal embryonic development. Mutations to the FGD1 gene result in a human developmental disorder affecting specific skeletal structures, including elements of the face, cervical vertebrae and distal extremities. Homozygous Vav-/- knockout mice embryos are not viable past the blastocyst stage, indicating an essential role of Vav in embryonic implantation. RESULTS: Here, we show that the microinjection of FGD1 and Vav into Swiss 3T3 fibroblasts induces the polymerization of actin and the assembly of clustered integrin complexes. FGD1 activates Cdc42, whereas Vav activates Rho, Rac and Cdc42. In addition, FGD1 and Vav stimulate the mitogen activated protein kinase cascade that leads to activation of the c-Jun kinase SAPK/JNK1. CONCLUSIONS: We conclude that FGD1 and Vav are regulators of the Rho GTPase family. Along with their target proteins Cdc42, Rac and Rho, FGD1 and Vav control essential signals required during embryonic development.

CDC42 and FGD1 cause distinct signaling and transforming activities.

Activated forms of different Rho family members (CDC42, Rac1, RhoA, RhoB, and RhoG) have been shown to transform NIH 3T3 cells as well as contribute to Ras transformation. Rho family guanine nucleotide exchange factors (GEFs) (also known as Dbl family proteins) that activate CDC42, Rac1, and RhoA also demonstrate oncogenic potential. The faciogenital dysplasia gene product, FGD1, is a Dbl family member that has recently been shown to function as a CDC42-specific GEF. Mutations within the FGD1 locus cosegregate with faciogenital dysplasia, a multisystemic disorder resulting in extensive growth impairments throughout the skeletal and urogenital systems. Here we demonstrate that FGD1 expression is sufficient to cause tumorigenic transformation of NIH 3T3 fibroblasts. Although both FGD1 and constitutively activated CDC42 cooperated with Raf and showed synergistic focus-forming activity, both quantitative and qualitative differences in their functions were seen. FGD1 and CDC42 also activated common nuclear signaling pathways. However, whereas both showed comparable activation of c-Jun, CDC42 showed stronger activation of serum response factor and FGD1 was consistently a better activator of Elk-1. Although coexpression of FGD1 with specific inhibitors of CDC42 function demonstrated the dependence of FGD1 signaling activity on CDC42 function, FGD1 signaling activities were not always consistent with the direct or exclusive stimulation of CDC42 function. In summary, FGD1 and CDC42 signaling and transformation are distinct, thus suggesting that FGD1 may be mediating some of its biological activities through non-CDC42 targets.

Sequence and structure correlation of human ribosomal transcribed spacers.

We report the sequences of the transcribed spacers of human rRNA that now allow us to piece together the entire primary transcript sequence of approximately 13.3 x 10(3) base-pairs. Comparison of transcribed spacer sequences with those of variable regions of rRNA and with those of the non-transcribed spacers supports the hypothesis that the variable regions are descended from transcribed spacers. Nucleotide sequence-derived secondary structures for the 5' external transcribed spacer and for internal transcribed spacers 1 and 2 match both the sizes and shapes of the structures that were visualized 15 years ago on electron micrographs. Parts of these structures are conserved in mammals and may be related to transcript processing.

Isolation, characterization, and mapping of the mouse Fgd3 gene, a new Faciogenital Dysplasia (FGD1; Aarskog Syndrome) gene homologue.

FGD1 gene mutations result in faciogenital dysplasia (FGDY, Aarskog syndrome), an X-linked developmental disorder that adversely affects the formation of multiple skeletal structures. FGD1 encodes a guanine nucleotide exchange factor (GEF) that specifically activates the Rho GTPase Cdc42. By way of Cdc42, FGD1 regulates the actin cytoskeleton and activates the c-Jun N-terminal kinase signaling cascade to regulate cell growth and differentiation. Previous work shows that FGD1 is the founding member of a family of related genes including the mouse Fgd2 gene and the rat Frabin gene. Here, we report on the isolation, characterization, and mapping of the mouse Fgd3 gene, a new and novel member of the FGD1 gene family. Fgd3 cDNA encodes a 733-amino-acid protein with a predicted mass of 81 kDa. Fgd3 and FGD1 share a high degree of sequence identity that spans >560 contiguous amino acid residues. Like FGD1, Fgd3 contains adjacent RhoGEF and pleckstrin homology (PH) domains, a second carboxy-terminal PH domain, and a distinctive FYVE domain. Together, these domains appear to form a canonical core structure for FGD1 family members. In addition, compared to other FGD1 family members, Fgd3 contains different structural regions that may be involved in distinct signaling interactions. Microinjection studies show that Fgd3 stimulates fibroblasts to form filopodia, actin microspikes formed upon the stimulation of Cdc42. Fgd3 transcripts are present in several diverse tissues and during mouse embryogenesis, suggesting a developmentally regulated pattern of expression and a potential role in embryonic development. Genetic linkage and radiation hybrid mapping data show that Fgd3 and the human FGD3 ortholog map to syntenic regions of murine chromosome 13 and human chromosome 9q22, respectively. We conclude that Fgd3 is a new and novel member of the FGD1 family of RhoGEF proteins.

Father-to-daughter transmission of focal dermal hypoplasia associated with nonrandom X-inactivation: support for X-linked inheritance and paternal X chromosome mosaicism.

Focal dermal hypoplasia (FDH) is a rare syndrome of severe developmental anomalies of the tissues and organs derived from ectoderm and mesoderm. Though data have suggested that FDH is an X-linked dominant trait associated with male hemizygote lethality, a hypothesis supported by the observation of three unrelated infants with FDH manifestations and de novo chromosome rearrangements involving Xp22, observations of father-to-daughter transmission have suggested possible genetic heterogeneity and autosomal dominant inheritance with sex limitation. We hypothesize that, if FDH is an X-linked disorder, cells expressing an active disease locus might experience a selective disadvantage resulting in a nonrandom pattern of X-inactivation in patient tissue. To test this hypothesis, we studied one of the two previously described families demonstrating father-to-daughter inheritance of FDH. To determine if the affected daughter had a skewed pattern of X-inactivation consistent with X-linked inheritance of FDH, somatic cell hybrids were constructed by fusing hypoxanthine phosphoribosyl transferase (HPRT)-deficient rodent fibroblasts with either patient dermal fibroblasts or peripheral white blood cells (WBCs); hybrid clones retaining an active X chromosome were analyzed to determine the parental origin of the active X chromosome. Analyses of resulting hybrid clones showed that while hybrids constructed from skin fibroblasts contained an active X chromosome inherited from either of the patient's parents, hybrids constructed from WBCs showed a skewed pattern of X-inactivation; 11 of 11 hybrids contained an active maternal X chromosome (chi 2 = 12.2, P = .001).(ABSTRACT TRUNCATED AT 250 WORDS)

Retinitis pigmentosa, growth hormone deficiency, and acromelic skeletal dysplasia in two brothers: possible familial RHYNS syndrome.

Here we report two brothers with retinitis pigmentosa, growth hormone deficiency, and acromelic skeletal dysplasia. We propose that their clinical picture is consistent with RHYNS syndrome (retinitis pigmentosa, hypopituitarism, nephronophthisis, and skeletal dysplasia) and that they represent the first instance of a familial occurrence of this syndrome. The presence of RHYNS in two siblings supports an autosomal recessive mode of inheritance; however, since all four known cases were male, an X-linked mode of inheritance cannot be excluded. The combination of clinical features found in these affected males is unique and supports the existence of RHYNS syndrome as a separate and distinct entity.

CHARGE association with choanal atresia and inner ear hypoplasia in a child with a de novo chromosome translocation t(2;7)(p14;q21.11).

A 3-year-old boy was diagnosed with CHARGE association on the basis of bilateral choanal atresia, absence of the semicircular canals, hypoplastic cochleae, genital hypoplasia, growth and developmental delays, cranial nerve dysfunction, and facial anomalies. Ophthalmologic and cardiac evaluations were normal. He was found to have an apparently balanced t(2;7)(p14;q21.11) chromosomal translocation. Parental karyotypes were normal. Although there is evidence suggesting a genetic basis for CHARGE association, individuals with chromosomal abnormalities and CHARGE are rare. In the described patient, the presence of characteristic CHARGE features suggests that the t(2;7)(p14;q21.11) translocation breakpoints may cause a deletion or disruption of genes within the involved regions that are involved in the generation of the CHARGE association phenotype.

A child with multiple congenital anomalies and karyotype 46,XY,del(14)(q31q32.3): further delineation of chromosome 14 interstitial deletion syndrome.

We report on an infant with a multiple congenital anomaly syndrome and severe developmental delay in association with a previously undescribed de novo interstitial deletion of chromosome 14 [karyotype: 46,XY,del(14) (q31q32.3)]. Comparison of the presented patient with previously reported cases of interstitial and terminal chromosome 14q deletions provides a group of patients monosomic for various overlapping portions of the distal half of chromosome 14q and suggests a limited similarity in phenotype among patients with common deleted 14q segments. All patients with distal 14q deletions were developmentally delayed, most were microcephalic and failed to thrive. Most of the patient's anomalies were limited to the face and head. Few major internal congenital anomalies were observed. These comparisons serve to further clarify possible associations of subchromosomal aberrations with specific phenotypes.

Reproductive risks for carriers of complex chromosome rearrangements: analysis of 25 families.

We have determined the empirical reproductive risks for heterozygous carriers of complex chromosome rearrangements (CCRs). CCRs are structural rearrangements involving at least three chromosomes and three or more chromosomal breakpoints. Pregnancy outcome, the frequency and type of chromosomal imbalance in the offspring, and the localization and distribution of chromosome breakpoints were analyzed in 25 CCR families ascertained by the birth of a malformed child or repeated spontaneous abortions. This study included two newly ascertained familial CCRs and a total of 67 informative pregnancies. Analysis of the data, after correction for ascertainment bias, showed that the incidence of spontaneous abortions in CCR families was 48.3%. Approximately one in ten pregnancies and 18.4% of all live births to CCR carriers resulted in phenotypically abnormal offspring. One-half of all CCR carrier liveborn offspring were also CCR carriers. There was a 53.7% incidence of an abnormal pregnancy outcome to CCR carriers. We failed to detect any evidence for a non-random involvement of specific chromosomes in CCRs. However, we did observe a non-random distribution of specific breakpoints at sites 1q25, 4q13, 6q27, 7p14, 9q12, 11p11, 11p15, 12q21, 13q31, and 18q21.

Terminal deletion of the long arm of chromosome 2 in a mildly dysmorphic hypotonic infant with karyotype 46,XY,del(2)(q37).

We describe a boy with severe hypotonia and minor facial anomalies with a terminal deletion of chromosome 2q (46,XY,del(2)(q37)). Comparison with previous cases in the literature indicates that this particular deletion results in infantile hypotonia, developmental delay, and minor craniofacial anomalies including frontal bossing and micrognathia. The absence of true malformations and few minor anomalies in this patient suggests that indications for obtaining a chromosome analysis from neurologically impaired individuals need to be reevaluated.

Cytogenetic and molecular analysis of inv dup(15) chromosomes observed in two patients with autistic disorder and mental retardation.

A variety of distinct phenotypes has been associated with supernumerary inv dup(15) chromosomes. Although different cytogenetic rearrangements have been associated with distinguishable clinical syndromes, precise genotype-phenotype correlations have not been determined. However, the availability of chromosome 15 DNA markers provides a means to characterize inv dup(15) chromosomes in detail to facilitate the determination of specific genotype-phenotype associations. We describe 2 patients with an autistic disorder, mental retardation, developmental delay, seizures, and supernumerary inv dup(15) chromosomes. Conventional and molecular cytogenetic studies confirmed the chromosomal origin of the supernumerary chromosomes and showed that the duplicated region extended to at least band 15q13. An analysis of chromosome 15 microsatellite CA polymorphisms suggested a maternal origin of the inv dup(15) chromosomes and biparental inheritance of the two intact chromosome 15 homologs. The results of this study add to the existing literature which suggests that the clinical phenotype of patients with a supernumerary inv dup(15) chromosome is determined not only by the extent of the duplicated region, but by the dosage of genes located within band 15q13 and the origin of the normal chromosomes 15.

XY sex reversal and gonadal dysgenesis due to 9p24 monosomy.

We describe a case of XY sex reversal, gonadal dysgenesis, and gonadoblastoma in a patient with a deletion of 9p24 due to a familial translocation. The rearranged chromosome 9 was inherited from the father; the patient's karyotype was 46,XY,der(9)t(8;9) (p21;p24)pat. A review shows that 6 additional patients with 46,XY sex reversal associated with monosomy of the distal short arm of chromosome 9 have been observed. The observation that all 7 patients with sex reversal share a deletion of the distal short arm of chromosome 9 is consistent with the hypothesis that the region 9p24 contains a gene or genes necessary for male sex determination. This present case narrows the chromosome interval containing a critical sex determination gene to the relatively small region 9p24. A molecular analysis of this region will provide a means to identify a gene involved in male sex determination.

Familial Mondini dysplasia.

OBJECTIVES/HYPOTHESIS: To determine the mode of inheritance of familial nonsyndromic Mondini dysplasia. STUDY DESIGN: Correlative clinical genetic analysis of a single kindred. METHODS: Clinical history, physical examination, audiologic analysis, computed tomography of the temporal bones, and cytogenetic analysis. RESULTS: The male proband, three affected sisters, and an affected brother are offspring of unaffected parents. The mother and an unaffected brother have audiologic findings suggestive of heterozygous carrier status for a recessive hearing loss gene. CONCLUSIONS: Pedigree analysis indicates autosomal recessive inheritance in this family. The observed inheritance and clinical, audiologic, and radiologic findings are different from those previously described for another family with nonsyndromic Mondini dysplasia. The phenotype in this study family therefore represents a distinct subtype, indicating clinical and genetic heterogeneity of this disorder. This information should facilitate future molecular linkage analyses and genetic counselling of patients with inner ear malformations.

Further Evidence of Contrasting Phenotypes Caused by Reciprocal Deletions and Duplications: Duplication of NSD1 Causes Growth Retardation and Microcephaly.

Microduplications of the Sotos syndrome region containing NSD1 on 5q35 have recently been proposed to cause a syndrome of microcephaly, short stature and developmental delay. To further characterize this emerging syndrome, we report the clinical details of 12 individuals from 8 families found to have interstitial duplications involving NSD1, ranging in size from 370 kb to 3.7 Mb. All individuals are microcephalic, and height and childhood weight range from below average to severely restricted. Mild-to-moderate learning disabilities and/or developmental delay are present in all individuals, including carrier family members of probands; dysmorphic features and digital anomalies are present in a majority. Craniosynostosis is present in the individual with the largest duplication, though the duplication does not include MSX2, mutations of which can cause craniosynostosis, on 5q35.2. A comparison of the smallest duplication in our cohort that includes the entire NSD1 gene to the individual with the largest duplication that only partially overlaps NSD1 suggests that whole-gene duplication of NSD1 in and of itself may be sufficient to cause the abnormal growth parameters seen in these patients. NSD1 duplications may therefore be added to a growing list of copy number variations for which deletion and duplication of specific genes have contrasting effects on body development.

The molecular genetics of incontinentia pigmenti.

Incontinentia pigmenti (IP) is an unusual and fascinating disorder of the developing neuroectoderm. IP is an X-linked dominant disease characterized by congenital and age-related dermatologic abnormalities and significant neurological, ophthalmologic, and dental anomalies. Two distinct IP gene loci, IP1, mapped to Xp11.21, and IP2, mapped to Xq28, have been identified. The necessary prerequisites for cloning the IP1 gene by a positional cloning approach are available. Ten DNA markers have been mapped to a region between IP1 X-chromosomal translocation breakpoints within region Xp11.21. Approximately 60% of the 2,500-kb region between IP1 X-chromosomal translocation breakpoints has been cloned in yeast artificial chromosome clones.

Isolation, characterization, and mapping of the mouse and human Fgd2 genes, faciogenital dysplasia (FGD1; Aarskog syndrome) gene homologues.

FGD1 encodes a guanine nucleotide exchange factor (GEF) that specifically activates the Rho GTPase Cdc42. FGD1 gene mutations result in faciogenital dysplasia (FGDY, Aarskog syndrome), an X-linked developmental disorder that adversely affects the formation of multiple skeletal structures. Database searches show that the Caenorhabditis elegans genome contains an FGD1 homologue. Since C. elegans genes often have multiple vertebrate homologues, we hypothesized the existence of multiple mammalian FGD1-related sequences. Here we report the use of degenerate PCR to isolate and characterize the mouse and human Fgd2 genes, new members of the FGD1 gene family. Fgd2 cDNA encodes a 727-amino-acid protein with a predicted mass of 82 kDa. Fgd2 and FGD1 share a high degree of sequence identity that spans >560 contiguous amino acid residues. Fgd2, like FGD1, contains adjacent RhoGEF and PH domains, a second carboxy-terminal PH domain, and a distinctive FYVE domain. Genomic PCR studies indicate some degree of conserved gene structure between Fgd2 and FGD1. Fgd2 transcripts are present in several diverse tissues and during mouse embryogenesis, suggesting a role in embryonic development. Genetic linkage and radiation hybrid mapping data show that Fgd2 and the human FGD2 ortholog map to syntenic regions of murine chromosome 17 and human chromosome 6p21.2, respectively. The observation that all FGD1 gene family members contain equivalent signaling domains and a conserved structural organization strongly suggests that these signaling domains form a canonical core structure for members of the FGD1 family of RhoGEF proteins.

An intragenic TaqI polymorphism in the faciogenital dysplasia (FGD1) locus, the gene responsible for Aarskog syndrome.

A Taq1 polymorphism, located in intron 4 of the faciogenital dysplasia (FGD1) gene, the gene responsible for Aarskog syndrome, is described. FGD1 encodes a putative Rho/Rac guanine nucleotide exchange factor involved in mammalian morphogenesis. The identification of an intragenic polymorphism will facilitate the accurate carrier detection of individuals at risk for Aarskog syndrome.