X-linked Opitz syndrome: novel mutations in the MID1 gene and redefinition of the clinical spectrum

Opitz (or G/BBB) syndrome is a pleiotropic genetic disorder characterized by hypertelorism, hypospadias, and additional midline defects. This syndrome is heterogeneous with an X-linked (XLOS) and an autosomal dominant (ADOS) form. The gene implicated in the XLOS form, MID1, encodes a protein containing a RING-Bbox-Coiled-coil motif belonging to the tripartite motif (TRIM) family. To further clarify the molecular basis of XLOS, we have undertaken mutation analysis of the MID1 gene in patients with Opitz syndrome (OS). We found novel mutations in 11 of 63 male individuals referred to us as sporadic or familial X-linked OS cases. The mutations are scattered throughout the gene, although more are represented in the 3' region. By reviewing all the MID1-mutated OS patients so far described, we confirmed that hypertelorism and hypospadias are the most frequent manifestations, being present in almost every XLOS individual. However, it is clear that laryngo-tracheo-esophageal (LTE) defects are also common anomalies, being manifested by all MID1-mutated male patients. Congenital heart and anal abnormalities are less frequent than reported in literature. In addition, we can include limb defects in the OS clinical synopsis as we found a MID1-mutated patient showing syndactyly. The low frequency of mutations in MID1 and the high variability of the phenotype suggest the involvement of other genes in the OS phenotype.     

Mild phenotypes in a series of patients with Opitz GBBB syndrome with MID1 mutations

Opitz syndrome (OS; MIM 145410 and MIM 300000) is a congenital midline malformation syndrome characterized by hypertelorism, hypospadias, cleft lip/palate, laryngotracheoesophageal (LTE) abnormalities, imperforate anus, developmental delay, and cardiac defects. The X-linked form (XLOS) is caused by mutations in the MID1 gene, which encodes a microtubule-associated RBCC protein. In this study, phenotypic manifestations of patients with and without MID1 mutations were compared to determine genotype-phenotype correlations. We detected 10 novel mutations, 5 in familial cases, 2 in sporadic cases, and 3 in families for whom it was not clear if they were familial or sporadic. The genotype and phenotype was compared for these 10 families, clinically diagnosed OS patients found not to have MID1 mutations, and 4 families in whom we have previously reported MID1 mutations. This combined data set includes clinical and mutation data on 70 patients. The XLOS patients with MID1 mutations were less severely affected than patients with MID1 mutations reported in previous studies, particularly in functionally significant neurologic, LTE, anal, and cardiac abnormalities. Minor anomalies were more prevalent in patients with MID1 mutations compared to those without mutations in this study. Female MID1 mutation carriers had milder phenotypes compared to male MID1 mutation carriers, with the most common manifestation being hypertelorism in both sexes. Most of the anomalies found in the patients of the present study do not correlate with the MID1 mutation type, with the possible exception of LTE malformations. This study demonstrates the wide spectrum of severity and manifestations of OS. It also shows that XLOS patients with MID1 mutations may be less severely affected than indicated in prior reports.     

A MID1 gene mutation in a patient with Opitz G/BBB syndrome that altered the 3D structure of SPRY domain

Mutations in the MID1 gene result in X-linked Opitz G/BBB syndrome (OS), a disorder that affects development of midline structures and comprises hypertelorism, cleft lip/palate, hypospadias, and laryngo-tracheo-esophageal abnormalities, and, at times, neurological, anal, and cardiac defects. MID1 gene abnormalities include missense, nonsense, and splicing mutations, small insertions, small deletions, and complex rearrangements. Here, we present a patient with Opitz G/BBB syndrome and a unique MID1 gene point mutation c.1703T相似文献   

MID1 mutation screening in a large cohort of Opitz G/BBB syndrome patients: twenty-nine novel mutations identified

Opitz G/BBB Syndrome (OS) is a multiple congenital anomaly disorder characterized by defects along the body midline. The disease is characterized by variable expressivity of signs that include hypertelorism, cleft lip and/or palate, laryngo-tracheo-esophageal abnormalities, cardiac defects, and hypospadias. OS patients also present with mental retardation and brain anatomical abnormalities. An autosomal dominant form mapping to chromosome 22 and an X-linked form of OS are known. The gene responsible for the X-linked form of OS, MID1, codes for a member of the Tripartite Motif family of E3 ubiquitin ligases. Here we report 29 novel mutations in 29 unrelated patients of a cohort of 140 male OS cases. These mutations are found in both familial and sporadic cases. They are scattered along the entire length of the gene and are represented by missense and nonsense mutations, insertions and deletions causing frame shift mutations, and deletion of either single exons or the entire gene. The variety of the mutations found confirms that loss-of-function is the mechanism underlying the OS phenotype. Moreover, the low percentage of MID1-mutated OS patients, 47% of the familial and 13% of the sporadic cases, suggests a wider genetic heterogeneity underlying the OS phenotype.     

New mutations in MID1 provide support for loss of function as the cause of X-linked Opitz syndrome

Opitz syndrome (OS) is a genetically heterogeneous malformation disorder. Patients with OS may present with a variable array of malformations that are indicative of a disturbance of the primary midline developmental field. Mutations in the C-terminal half of MID1, an RBCC (RING, B-box and coiled-coil) protein, have recently been shown to underlie the X-linked form of OS. Here we show that the MID1 gene spans at least 400 kb, almost twice the distance originally reported and has a minimum of six mRNA isoforms as a result of the alternative use of 5' untranslated exons. In addition, our detailed mutational analysis of MID1 in a cohort of 15 patients with OS has resulted in the identification of seven novel mutations, two of which disrupt the N-terminus of the protein. The most severe of these (E115X) is predicted to truncate the protein before the B-box motifs. In a separate patient, a missense change (L626P) was found that also represents the most C-terminal alteration reported to date. As noted with other C-terminal mutations, GFP fusion constructs demonstrated that the L626P mutant formed cytoplasmic clumps in contrast to the microtubular distribution seen with the wild-type sequence. Notably, however, both N-terminal mutants showed no evidence of cytoplasmic aggregation, inferring that this feature is not pathognomonic for X-linked OS. These new data and the finding of linkage to MID1 in the absence of a demonstrable open reading frame mutation in a further family support the conclusion that X-linked OS results from loss of function of MID1.     

Isolation and embryonic expression of the novel mouse gene Hic1, the homologue of HIC1, a candidate gene for the Miller-Dieker syndrome

The human gene HIC1 (hypermethylated in cancer) maps to chromosome 17p13.3 and is deleted in the contiguous gene disorder Miller-Dieker syndrome (MDS) [Makos-Wales et al. (1995) Nature Med., 1, 570-577; Chong et al. (1996) Genome Res., 6, 735-741]. We isolated the murine homologue Hic1, encoding a zinc-finger protein with a poxvirus and zinc-finger (POZ) domain and mapped it to mouse chromosome 11 in a region exhibiting conserved synteny to human chromosome 17. Comparison of genomic and cDNA sequences predicts two exons for the murine Hic1. The second exon exhibits 88% identity to the human HIC1 on DNA level. During embryonic development, Hic1 is expressed in mesenchymes of the sclerotomes, lateral body wall, limb and cranio-facial regions embedding the outgrowing peripheral nerves during their differentiation. During fetal development, Hic1 additionally is expressed in mesenchymes apposed to precartilaginous condensations, at many interfaces to budding epithelia of inner organs, and weakly in muscles. We observed activation of Hic1 expression in the embryonic anlagen of many tissues displaying anomalies in MDS patients. Besides lissencephaly, MDS patients exhibit facial dysmorphism and frequently additional birth defects, e.g. anomalies of the heart, kidney, gastrointestinal tract and the limbs (OMIM 247200). Thus, HIC1 activity may correlate with the defective development of the nose, jaws, extremities, gastrointestinal tract and kidney in MDS patients.     

Clinical and molecular studies of patients with characteristics of Opitz G/BBB syndrome shows a novel MID1 mutation

Opitz G/BBB syndrome is characterized by midline abnormalities such as hypertelorism, cleft palate, and hypospadias. This syndrome is heterogeneous with an X-linked recessive form caused by mutations in the MID1 gene at band Xp22.3. However, mutations in MID1 have only been identified in 47% of familial cases of X-linked Opitz G/BBB syndrome, and 13% of sporadic cases. We performed a phenotype-genotype analysis of a group of nine new patients with clinical characteristics commonly seen in Opitz G/BBB syndrome, and of previously reported patients. We identified a novel mutation in exon 9 of the MID1 gene, c.1941insTGAGTCATCATCC, leading to a premature termination codon at amino acid 514 in a patient with hypertelorism, apparently low-set ears, a short philtrum, bilateral cleft of lip and palate and hypospadias. This mutation affects the PRY domain of the C-terminus of the MID1 protein.     

WFS1 (Wolfram syndrome 1) gene product: predominant subcellular localization to endoplasmic reticulum in cultured cells and neuronal expression in rat brain

Wolfram (DIDMOAD) syndrome is an autosomal recessive neurodegenerative disorder accompanied by insulin-dependent diabetes mellitus and progressive optic atrophy. Recent positional cloning led to identification of the WFS1 (Wolfram syndrome 1) gene, a member of a novel gene family of unknown function. In this study, we generated a specific antibody against the C-terminus of the WFS1 protein and investigated its subcellular localization in cultured cells. We also studied its distribution in the rat brain. Biochemical studies indicated the WFS1 protein to be an integral, endoglycosidase H-sensitive membrane glycoprotein that localizes primarily in the endoplasmic reticulum (ER). Consistent with this, immunofluorescence cell staining of overexpressed WFS1 showed a characteristic reticular pattern over the cytoplasm and overlapped with the ER marker staining. No co-localization of WFS1 with mitochondria argues against an earlier clinical hypothesis that Wolfram syndrome is a mitochondria-mediated disorder. In the rat brain, at both the protein and mRNA level, WFS1 was found to be present predominantly in selected neurons in the hippocampus CA1, amygdaloid areas, olfactory tubercle and superficial layer of the allocortex. These expression sites, i.e. components of the limbic system or structures closely associated with this system, may be involved in the psychiatric, behavioral and emotional abnormalities characteristic of this syndrome. ER localization of WFS1 suggests that this protein plays an as yet undefined role in membrane trafficking, protein processing and/or regulation of ER calcium homeostasis. These studies represent a first step toward the characterization of WFS1 protein, which presumably functions to maintain certain populations of neuronal and endocrine cells.     

Btg1 and Btg2 gene expression during early chick development

Btg/Tob genes encode for a new family of proteins with antiproliferative functions, which are also able to stimulate cell differentiation. Btg1 and Btg2 are the most closely related members in terms of gene sequence. We analyzed their expression patterns in avian embryos by in situ hybridization, from embryonic day 1 to 3. Btg1 was distinctively expressed in the Hensen's node, the notochord, the cardiogenic mesoderm, the lens vesicle, and in the apical ectodermal ridge and mesenchyme of the limb buds. On the other hand, Btg2 expression domains included the neural plate border, presomitic mesoderm, trigeminal placode, and mesonephros. Both genes were commonly expressed in the myotome, epibranchial placodes, and dorsal neural tube. The results suggest that Btg1 and Btg2 are involved in multiple developmental processes. Overlapping expression of Btg1 and Btg2 may imply redundant functions, but unique expression patterns suggest also differential regulation and function.     

Differential expression and subcellular localization of secretogranin II and synaptophysin during early development of mouse hypothalamic neurons in culture.

Mature neurons contain two distinct regulated secretory pathways, characterized electron microscopically by so-called large dense core vesicles and small synaptic vesicles, respectively. Each vesicle type is characterized by vesicle-specific proteins, such as the granins (chromogranins/secretogranins) for the matrix of large dense core vesicles and synaptophysin for the membrane of small synaptic vesicles. So far, no data exist on the biogenesis of these two distinct vesicle types during neuronal development. We have used secretogranin II and synaptophysin as markers for the biogenesis of these two vesicle types during the development of mouse hypothalamic neurons in culture, using immunocytochemistry and biochemical analyses. By immunofluorescence, we found that secretogranin II appears as early as synaptophysin, but in a subset of neurons only, and with different subcellular localizations. It was observed in cytoplasmic areas where little or no synaptophysin immunofluorescence was detected, such as lamellipodia, emerging neurites and growth cones. At later stages, the proportion of secretogranin II-containing varicosities remained steady whereas that of synaptophysin-containing varicosities increased dramatically. By quantitative analysis we found that the level of expression of synaptophysin increased several-fold during synaptogenesis whereas that of secretogranin II decreased. These data suggest that large dense core vesicles and small synaptic vesicles can be formed separately and expressed at different levels. They provide evidence for a differential biogenesis of these two distinct vesicle types.     

Regulation of the neurofibromatosis 2 gene promoter expression during embryonic development.

Mutations in the Neurofibromatosis 2 (NF2) gene are associated with predisposition to vestibular schwannomas, spinal schwannomas, meningiomas, and ependymomas. Presently, how NF2 is expressed during embryonic development and in the tissues affected by neurofibromatosis type 2 (NF2) has not been well defined. To examine NF2 expression in vivo, we generated transgenic mice carrying a 2.4-kb NF2 promoter driving beta-galactosidase (beta-gal) with a nuclear localization signal. Whole-mount embryo staining revealed that the NF2 promoter directed beta-gal expression as early as embryonic day E5.5. Strong expression was detected at E6.5 in the embryonic ectoderm containing many mitotic cells. beta-gal staining was also found in parts of embryonic endoderm and mesoderm. The beta-gal staining pattern in the embryonic tissues was corroborated by in situ hybridization analysis of endogenous Nf2 RNA expression. Importantly, we observed strong NF2 promoter activity in the developing brain and in sites containing migrating cells including the neural tube closure, branchial arches, dorsal aorta, and paraaortic splanchnopleura. Furthermore, we noted a transient change of NF2 promoter activity during neural crest cell migration. While little beta-gal activity was detected in premigratory neural crest cells at the dorsal ridge region of the neural fold, significant activity was seen in the neural crest cells already migrating away from the dorsal neural tube. In addition, we detected considerable NF2 promoter activity in various NF2-affected tissues such as acoustic ganglion, trigeminal ganglion, spinal ganglia, optic chiasma, the ependymal cell-containing tela choroidea, and the pigmented epithelium of the retina. The NF2 promoter expression pattern during embryogenesis suggests a specific regulation of the NF2 gene during neural crest cell migration and further supports the role of merlin in cell adhesion, motility, and proliferation during development.     

Live imaging of endogenous periodic tryptophan protein 2 gene homologue during zebrafish development

Yeast Periodic tryptophan protein 2 gene (Pwp2) is involved in ribosome biogenesis and has been implicated in regulation of the cell cycle in yeast. Here, we report a zebrafish protein-trap line that produces fluorescently tagged Periodic tryptophan protein 2 gene homologue (Pwp2h) protein, which can be dynamically tracked in living fish at subcellular resolution. We identified both full-length zebrafish Pwp2h and a short variant. The expression results show that Pwp2h is present in numerous sites in the early developing embryo, but later is restricted to highly proliferative regions, including the forebrain ventricular zone and endoderm-derived organs in the early larval stage. At the subcellular level, Pwp2h protein appears to be localized to the region of the nucleolus consistent with its presumed function in ribosomal RNA synthesis. This Pwp2h protein trap line offers a powerful tool to study the link between ribosome biogenesis and cell cycle progression during vertebrate development.