Peroxisome proliferator-activated receptor ␥ (PPAR␥) plays a crucial role in adipocyte differentiation, glucose metabolism, and other physiological processes. To further explore the role of PPAR␥ in adipose tissues, we used a Cre͞loxP strategy to generate adipose-specific PPAR␥ knockout mice. These animals exhibited marked abnormalities in the formation and function of both brown and white adipose tissues. When fed a high-fat diet, adiposespecific PPAR␥ knockout mice displayed diminished weight gain despite hyperphagia, had diminished serum concentrations of both leptin and adiponectin, and did not develop glucose intolerance or insulin resistance. Characterization of in vivo glucose dynamics pointed to improved hepatic glucose metabolism as the basis for preventing high-fat diet-induced insulin resistance. Our findings further illustrate the essential role for PPAR␥ in the development of adipose tissues and suggest that a compensatory induction of hepatic PPAR␥ may stimulate an increase in glucose disposal by the liver.body weight regulation ͉ diabetes ͉ knockout mouse ͉ Cre recombinase

Rett syndrome is caused by mutations in the gene MECP2 in ∼80% of affected individuals. We describe a previously unknown MeCP2 isoform. Mutations unique to this isoform and the absence, until now, of identified mutations specific to the previously recognized protein indicate an important role for the newly discovered molecule in the pathogenesis of Rett syndrome.Rett syndrome (RTT; OMIM 312750) is characterized by onset, in girls, of a gradual slowing of neurodevelopment in the second half of the first year of life that proceeds towards stagnation by age 4 years, followed by regression and loss of acquired fine motor and communication skills. A pseudostationary period follows during which a picture of preserved ambulation, aberrant communication and stereotypic hand wringing approximates early autism. Regression, however, remains insidiously ongoing and ultimately results in profound mental retardation 1 .Up to 80% of individuals with RTT have mutations 2,3 in exons 3 and 4 of the four-exon gene MECP2 (Fig. 1a) 4 encoding the transcriptional repressor MeCP2. In the known transcript of the gene, all four exons are used, the translation start site is in exon 2, and exon 1 and most of exon 2 form the 5′ untranslated region (UTR) 4 . For clarity, we refer to this transcript as MECP2A and its encoded protein as MeCP2A. We sought to identify MECP2 splice variants contributing new coding sequence that might contain mutations in the remaining individuals with RTT. Inspection of the 5′ UTR showed that, whereas exon 2 has a number of in-frame stop codons upstream of the ATG start codon, exon 1 contains an open reading frame across its entire length, including an ATG. Submitting a theoretical construct composed of exons 1, 3 and 4 to the ATGpr program (http://www.hri.co.jp/atgpr/), which predicts the likelihood that an ATG will be an initiation codon based on the significance of its surrounding Kozak nucleotide context, returned a reliability score of 97%, as compared with 64% for MECP2A. A search in EST databases identified eight examples of our theorized transcript, which we named MECP2B (Fig. 1b), as compared with 14 examples of MECP2A. MECP2B is predicted to encode a new isoform, MeCP2B, with an alternative, longer N terminus determined by exon 1 (see Supplementary Table 1 online).To confirm that MECP2B is expressed and not merely an artifact of cDNA library preparation, we amplified cDNA by PCR from a variety of tissues using a 5′ primer in exon 1 and a 3′ primer in exon 3 (Fig. 1a). We obtained two PCR products corresponding in size and sequence to MECP2A and MECP2B in all tissues, including fetal and adult brain and different brain subregions (Fig. 1c). Results in mouse were similar (Fig. 1c). We quantified the expression levels of the two transcripts in adult human brain. Expression of MECP2B was ten times higher than that of MECP2A (Fig. 1d). We studied the subcellular localization of MeCP2B after transfection of 3′ myc-tagged MECP2B into COS-7 cells and found it to be principally in the nucleus (Fig. 1e).To deter...

Background We aimed for a comprehensive delineation of genetic, functional and phenotypic aspects of GRIN2B encephalopathy and explored potential prospects of personalised medicine. Methods Data of 48 individuals with de novo GRIN2B variants were collected from several diagnostic and research cohorts, as well as from 43 patients from the literature. Functional consequences and response to memantine treatment were investigated in vitro and eventually translated into patient care. Results Overall, de novo variants in 86 patients were classified as pathogenic/likely pathogenic. Patients presented with neurodevelopmental disorders and a spectrum of hypotonia, movement disorder, cortical visual impairment, cerebral volume loss and epilepsy. Six patients presented with a consistent malformation of cortical development (MCD) intermediate between tubulinopathies and polymicrogyria. Missense variants cluster in transmembrane segments and ligand-binding sites. Functional consequences of variants were diverse, revealing various potential gain-of-function and loss-of-function mechanisms and a retained sensitivity to the use-dependent blocker memantine. However, an objectifiable beneficial treatment response in the respective patients still remains to be demonstrated. Conclusions In addition to previously known features of intellectual disability, epilepsy and autism, we found evidence that GRIN2B encephalopathy is also frequently associated with movement disorder, cortical visual impairment and MCD revealing novel phenotypic consequences of channelopathies.

Although many of the phenotypic features of our patients are rather nonspecific in cohorts of individuals with syndromic and nonsyndromic mental retardation, the proneness to infection is quite striking because the patients had normal growth and were not physically debilitated. Although the etiology of the infections is not understood, we recommend considering MECP2 dosage studies and a genetics referral in individuals with severe developmental delay and neurologic findings, especially when a history of recurrent respiratory ailments has been documented.