Fragile X syndrome arises from blocked expression of the fragile X mental retardation protein (FMRP). Golgi-impregnated mature cerebral cortex from fragile X patients exhibits long, thin, tortuous postsynaptic spines resembling spines observed during normal early neocortical development. Here we describe dendritic spines in Golgi-impregnated cerebral cortex of transgenic fragile X gene (Fmr1) knockout mice that lack expression of the protein. Dendritic spines on apical dendrites of layer V pyramidal cells in occipital cortex of fragile X knockout mice were longer than those in wild-type mice and were often thin and tortuous, paralleling the human syndrome and suggesting that FMRP expression is required for normal spine morphological development. Moreover, spine density along the apical dendrite was greater in the knockout mice, which may ref lect impaired developmental organizational processes of synapse stabilization and elimination or pruning.Fragile X syndrome is the most common inherited form of human mental retardation after Down Syndrome. It is an X-linked genetic trait with an incidence of 1͞2,000 in males (1-3). Phenotypic abnormalities include moderate to severe mental retardation, autistic behavior, macroorchidism, and facial abnormalities (1). The FMR1 gene contains a trinucleotide repeat [(CGG) n ] in the 5Ј untranslated region that is expanded (Ն200 repeats) in fragile X patients (2, 4, 5), resulting in hypermethylation of the FMR1 promoter region and absence of the encoded fragile X mental retardation protein (FMRP). Studies prior to the characterization of fragile X syndrome associated immature dendritic spine morphology (long and thin) with some forms of mental retardation (6-8). Similarly, fragile X cerebral cortical autopsy material exhibits thin, elongated spines and small synaptic contacts (9, 10).Recently, transgenic Fmr1 mice were produced in which the Fmr1 gene was disrupted in embryonic stem cells using a targeting vector to exon 5 and homologous recombination (11). The resultant homozygous knockout mice express no FMRP. Phenotypically, these mice exhibit increased testicular size and mildly impaired performance on the Morris water maze (11), paralleling human symptoms. To explore further parallels to the human syndrome, we examined the effect of the Fmr1 knockout on dendritic spines in the visual cortex using the Golgi-Cox impregnation technique. MATERIALS AND METHODSMale mutant (n ϭ 4) and wild-type FVB strain (n ϭ 4) adult (16-week-old) mice were prepared for Golgi-Cox impregnation. Mice were anesthetized with sodium pentobarbital (85 mg͞kg) and perfused transcardially with 60 ml of 0.9% NaCl (pH 7.3). Brains were removed and were cut sagittally along the midline. Tissue blocks were then immersed in 100 ml of Golgi-Cox solution (1% potassium dichromate͞1% mercuric chloride͞0.8% potassium chromate in distilled water) for 18 days. Tissue blocks were then immersed in 30% sucrose in 0.9% saline for 2 days and subsequently sectioned (200 m) using a vibratome. Sections were mounted o...

Cornelia de Lange syndrome (CdLS) is a dominantly inherited congenital malformation disorder caused by mutations in the cohesin-loading protein NIPBL1,2 for nearly 60% of individuals with classical CdLS3-5 and in the core cohesin components SMC1A (~5%) and SMC3 (<1%) for a smaller fraction of probands6,7. In humans, the multi-subunit complex cohesin is comprised of SMC1, SMC3, RAD21 and a STAG protein to form a ring structure proposed to encircle sister chromatids to mediate sister chromatid cohesion (SCC)8 as well as play key roles in gene regulation9. SMC3 is acetylated during S-phase to establish cohesiveness of chromatin-loaded cohesin10-13 and in yeast, HOS1, a class I histone deacetylase, deacetylates SMC3 during anaphase14-16. Here we report the identification of HDAC8 as the vertebrate SMC3 deacetylase as well as loss-of-function HDAC8 mutations in six CdLS probands. Loss of HDAC8 activity results in increased SMC3 acetylation (SMC3-ac) and inefficient dissolution of the “used” cohesin complex released from chromatin in both prophase and anaphase. While SMC3 with retained acetylation is loaded onto chromatin, ChIP-Seq analysis demonstrates decreased occupancy of cohesin localization sites that results in a consistent pattern of altered transcription seen in CdLS cell lines with either NIPBL or HDAC8 mutations.

Thoracic aortic aneurysms and dissections are a main feature of connective tissue disorders, such as Marfan syndrome and Loeys-Dietz syndrome. We delineated a new syndrome presenting with aneurysms, dissections and tortuosity throughout the arterial tree in association with mild craniofacial features and skeletal and cutaneous anomalies. In contrast with other aneurysm syndromes, most of these affected individuals presented with early-onset osteoarthritis. We mapped the genetic locus to chromosome 15q22.2-24.2 and show that the disease is caused by mutations in SMAD3. This gene encodes a member of the TGF-β pathway that is essential for TGF-β signal transmission. SMAD3 mutations lead to increased aortic expression of several key players in the TGF-β pathway, including SMAD3. Molecular diagnosis will allow early and reliable identification of cases and relatives at risk for major cardiovascular complications. Our findings endorse the TGF-β pathway as the primary pharmacological target for the development of new treatments for aortic aneurysms and osteoarthritis.

Fragile-X syndrome is a common form of mental retardation resulting from the inability to produce the fragile-X mental retardation protein. Qualitative examination of human brain autopsy material has shown that fragile-X patients exhibit abnormal dendritic spine lengths and shapes on parieto-occipital neocortical pyramidal cells. Similar quantitative results have been obtained in fragile-X knockout mice, that have been engineered to lack the fragile-X mental retardation protein. Dendritic spines on layer V pyramidal cells of human temporal and visual cortices stained using the Golgi-Kopsch method were investigated. Quantitative analysis of dendritic spine length, morphology, and number was carried out on patients with fragile-X syndrome and normal age-matched controls. Fragile-X patients exhibited significantly more long dendritic spines and fewer short dendritic spines than did control subjects in both temporal and visual cortical areas. Similarly, fragile-X patients exhibited significantly more dendritic spines with an immature morphology and fewer with a more mature type morphology in both cortical areas. In addition, fragile-X patients had a higher density of dendritic spines than did controls on distal segments of apical and basilar dendrites in both cortical areas. Long dendritic spines with immature morphologies and elevated spine numbers are characteristic of early development or a lack of sensory experience. The fact that these characteristics are found in fragile-X patients throughout multiple cortical areas may suggest a global failure of normal dendritic spine maturation and or pruning during development that persists throughout adulthood.