Biomedical subjects

Rodney C Samaco

Publications and source records attributed to Rodney C Samaco.

5 recordsLinked to original sources

PubMed2006

Expression of FoxP2 during zebrafish development and in the adult brain.

Fox (forkhead) genes encode transcription factors that play important roles in the regulation of embryonic patterning as well as in tissue specific gene expression. Mutations in the human FOXP2 gene cause abnormal speech development. Here we report the structure and expression pattern of zebrafish FoxP2. In zebrafish, this gene is first expressed at the 20-somite stage in the presumptive telencephalon. At this stage there is a significant overlap of FoxP2 expression with the expression of the emx homeobox genes. However, in contrast to emx1, FoxP2 is not expressed in the pineal gland or in the pronephric duct. After 72 hours of development, the expression of zebrafish FoxP2 becomes more complex in the brain. The developing optic tectum becomes the major area of FoxP2 expression. In the adult brain, the highest concentrations of the FoxP2 transcript can be observed in the optic tectum. In the cerebellum, only the caudal lobes show high levels of Foxp2 expression. These regions correspond to the vestibulocerebellum of mammals. Several other regions of the brain also show high levels of Foxp2 expression.

Amino Acid Sequence↗

PubMed2004

Epigenetic overlap in autism-spectrum neurodevelopmental disorders: MECP2 deficiency causes reduced expression of UBE3A and GABRB3.

Autism is a common neurodevelopmental disorder of complex genetic etiology. Rett syndrome, an X-linked dominant disorder caused by MECP2 mutations, and Angelman syndrome, an imprinted disorder caused by maternal 15q11-q13 or UBE3A deficiency, have phenotypic and genetic overlap with autism. MECP2 encodes methyl-CpG-binding protein 2 that acts as a transcriptional repressor for methylated gene constructs but is surprisingly not required for maintaining imprinted gene expression. Here, we test the hypothesis that MECP2 deficiency may affect the level of expression of UBE3A and neighboring autism candidate gene GABRB3 without necessarily affecting imprinted expression. Multiple quantitative methods were used including automated quantitation of immunofluorescence and in situ hybridization by laser scanning cytometry on tissue microarrays, immunoblot and TaqMan PCR. The results demonstrated significant defects in UBE3A/E6AP expression in two different Mecp2 deficient mouse strains and human Rett, Angelman and autism brains compared with controls. Although no difference was observed in the allelic expression of several imprinted transcripts in Mecp2-null brain, Ube3a sense expression was significantly reduced, consistent with the decrease in protein. A non-imprinted gene from 15q11-q13, GABRB3, encoding the beta3 subunit of the GABAA receptor, also showed significantly reduced expression in multiple Rett, Angelman and autism brain samples, and Mecp2 deficient mice by quantitative immunoblot. These results suggest an overlapping pathway of gene dysregulation within 15q11-q13 in Rett, Angelman and autism and implicate MeCP2 in the regulation of UBE3A and GABRB3 expressions in the postnatal mammalian brain.

Angelman Syndrome↗

PubMed2004

X-Chromosome inactivation ratios affect wild-type MeCP2 expression within mosaic Rett syndrome and Mecp2-/+ mouse brain.

Rett syndrome (RTT) is an X-linked neurodevelopmental disorder caused by mutations in MECP2, encoding methyl-CpG-binding protein 2 (MeCP2). The onset of symptoms in RTT is delayed until 6-18 months and 4-6 months in the Mecp2(-/+) mouse model, corresponding to a dynamic and gradual accumulation of MeCP2 expression in individual neurons of the postnatal brain. Because of X chromosome inactivation (XCI), cells within RTT females are mosaic for expression of the heterozygous MECP2 mutation. Using the targeted Mecp2 mouse model, we investigated the effect of Mecp2 mutation on XCI and developmental MeCP2 expression in wild-type (wt)-expressing neurons by quantitative laser scanning cytometry. Mecp2(-/+) female mice exhibited uniform regional distribution of Mecp2 mutant-expressing cells in brain, but unbalanced XCI in the population, favoring expression of the Mecp2 wt allele. Interestingly, MeCP2 expression in Mecp2 wt-expressing cells from Mecp2(-/+) mice was significantly lower than those from Mecp2(+/+) age-matched controls. The negative effect of Mecp2 mutation on wt Mecp2 expression correlated with the percentage of Mecp2 mutant-expressing cells in the cortex. Similar results were observed in two RTT females with identical MECP2 mutations but different XCI ratios. These results demonstrate that Mecp2-mutant neurons affect the development of surrounding neurons in a non-cell-autonomous manner and suggest that environmental influences affect the level of MeCP2 expression in wt neurons. These results help in explaining the role of XCI in the pathogenesis of RTT and have important implications in designing therapies for female RTT patients.

Animals↗

PubMed2004

Multiple pathways regulate MeCP2 expression in normal brain development and exhibit defects in autism-spectrum disorders.

Rett syndrome (RTT) is a neurodevelopmental disorder caused by mutations in MECP2, encoding methyl-CpG-binding protein 2 (MeCP2). Although MECP2 is ubiquitously transcribed, MeCP2 expression is developmentally regulated and heterogeneous in neuronal subpopulations, defined as MeCP2(lo) and MeCP2(hi). To test the hypothesis that pathways affecting MeCP2 expression changes may be defective in RTT, autism and other neurodevelopmental disorders without MECP2 mutations, a high-throughput quantitation of MeCP2 expression was performed on a tissue microarray containing frontal cortex samples from 28 different patients with neurodevelopmental disorders and age-matched controls. Combined quantitative analyses of MeCP2 protein and alternatively polyadenylated transcript levels were performed by laser scanning cytometry and tested for significant differences from age-matched controls. Normal cerebral samples showed an increase in total MeCP2 expression and the percentage of MeCP2(hi) cells with age that could be explained by increased MECP2 transcription within the MeCP2(hi) population. A significant decrease in the relative usage of the long transcript in the MeCP2(lo) population was observed in postnatal compared to fetal brain, but alternate polyadenylation did not correlate with MeCP2 expression changes at the single cell level. Brain samples from several related neurodevelopmental disorders, including autism, pervasive developmental disorder, Prader-Willi and Angelman syndromes showed significant differences in MeCP2 expression from age-matched controls by apparently different transcriptional and post-transcriptional mechanisms. These results suggest that multiple pathways regulate the complex developmental expression of MeCP2 and are defective in autism-spectrum disorders in addition to RTT.

Adolescent↗

PubMed2002

MECP2 mutations in Rett syndrome adversely affect lymphocyte growth, but do not affect imprinted gene expression in blood or brain.

Rett syndrome (RTT) is an X-linked dominant neurodevelopmental disorder caused by mutations in MECP2, encoding methyl-CpG-binding protein 2 (MeCP2). As female somatic cells are mosaic for expression of mutant MECP2, we performed single cell cloning of T lymphocytes from four RTT patients with MECP2 mutations to isolate cells expressing mutant MECP2. Mutant-expressing clones were present at a significantly lower frequency (P<0.0001) than wild-type clones. These results demonstrate that although MECP2 is not essential for lymphocyte growth, expression of the MECP2 mutation causes a growth disadvantage in cultured clonal T cells by reducing the response to mitogenic stimulation. Mutant MECP2 was expressed at normal transcript and protein levels, and exhibited no significant effect on acetylated histones or methyl-binding protein 3 (MBD3) levels. Since MeCP2 was predicted to silence transcription of methylated genes, we hypothesized that MeCP2 may be required for silencing imprinted or methylated gene expression. The allelic expression of three different imprinted genes (SNRPN, IPW and IGF2) was examined by RT-PCR and RFLP analysis, and demonstrated normal monoallelic expression of all RTT clones. We also examined the expression of five imprinted genes (SNRPN, IPW, NECDIN, H19 and IGF2) in RTT brain samples and observed exclusive monoallelic expression. Expression levels were also normal in MECP2 mutant-expressing T cells for IFNG, a non-imprinted, but methylated gene differentially expressed in T cells, and LINE-1 retrotransposons hypothesized to be silenced by MeCP2. The histone deacetylase inhibitor Trichostatin A did not alter SNRPN expression, but did reverse silencing of IFNG in a MECP2-mutant-expressing clone. In conclusion, our results do not support an essential role for either MeCP2 or HDAC in the silencing of several imprinted genes.

Acetylation↗