Biomedical subjects

Marika Charalambous

Publications and source records attributed to Marika Charalambous.

4 recordsLinked to original sources

PubMed2004

An enhancer element at the Igf2/H19 locus drives gene expression in both imprinted and non-imprinted tissues.

The insulin-like growth factor 2 (Igf2) gene encodes a potent growth factor that is expressed in multiple tissues during embryonic development. Expression at this locus is mediated by genomic imprinting. In the developing endodermal tissues, imprinting of Igf2 is mediated by the interaction of a set of enhancers downstream of the linked H19 gene with a differentially methylated domain (DMD) that lies approximately 2-4 kb upstream of H19 that has a boundary or insulator function in the hypomethylated state. In the remainder of tissues that express Igf2 and H19, the cis elements that drive their correct expression and imprinting are not well understood. In addition, enhancers driving expression of Igf2 in the choroid plexus and leptomeninges, tissues where the gene is thought not to be imprinted, have not been isolated. Here we show that biallelic (non-imprinted) expression within the choroid plexus is restricted to the epithelium, and we provide evidence that a conserved intergenic region functions as an enhancer for Igf2 both in tissues where the gene is imprinted, and where Igf2 is biallelically expressed. The presence of an enhancer for imprinted tissues in the intergenic region argues for the existence of imprinting controls distinct from the DMD, which may be provided by differential methylation at sites proximal to Igf2.

Animals↗

PubMed2004

BASP1 is a transcriptional cosuppressor for the Wilms' tumor suppressor protein WT1.

The Wilms' tumor suppressor protein WT1 is a transcriptional regulator that plays a key role in the development of the kidneys. The transcriptional activation domain of WT1 is subject to regulation by a suppression region within the N terminus of WT1. Using a functional assay, we provide direct evidence that this requires a transcriptional cosuppressor, which we identify as brain acid soluble protein 1 (BASP1). WT1 and BASP1 associate within the nuclei of cells that naturally express both proteins. BASP1 can confer WT1 cosuppressor activity in transfection assays, and elimination of endogenous BASP1 expression augments transcriptional activation by WT1. BASP1 is present in the developing nephron structures of the embryonic kidney and, coincident with that of WT1, its expression is restricted to the highly specialized podocyte cells of the adult kidney. Taken together, our results show that BASP1 is a WT1-associated factor that can regulate WT1 transcriptional activity.

Adult↗

PubMed2003

Evidence for a priming effect on maternal resource allocation: implications for interbrood competition.

It is commonly assumed that there exists interbrood competition mediated by in utero growth. This could be manifested by a female reallocating saved resources to future broods. Here, we report results of a manipulation experiment designed to detect such reallocation. Two groups of female mice were allowed each to produce two broods. In the first brood, the test females were mated with phenotypically normal males heterozygous for an insulin-like growth factor 2 (Igf2) null allele, while the control females were mated to a wild-type male. The test sample females invested 20% less into their first brood than did the control sample. In both test and control groups the females were mated with a wild-type male in the second round of mating. Surprisingly, we found that females that invested little into their first brood also invested little (compared with other second broods) into their second brood. This 'priming' effect suggests that the assumptions of classical models of parent-offspring conflict are overly simplistic but cannot disprove the existence of interbrood competition.

Animals↗

PubMed2003

Disruption of the imprinted Grb10 gene leads to disproportionate overgrowth by an Igf2-independent mechanism.

To investigate the function of the Grb10 adapter protein, we have generated mice in which the Grb10 gene was disrupted by a gene-trap insertion. Our experiments confirm that Grb10 is subject to genomic imprinting with the majority of Grb10 expression arising from the maternally inherited allele. Consistent with this, disruption of the maternal allele results in overgrowth of both the embryo and placenta such that mutant mice are at birth approximately 30% larger than normal. This observation establishes that Grb10 is a potent growth inhibitor. In humans, GRB10 is located at chromosome 7p11.2-p12 and has been associated with Silver-Russell syndrome, in which approximately 10% of those affected inherit both copies of chromosome 7 from their mother. Our results indicate that changes in GRB10 dosage could, in at least some cases, account for the severe growth retardation that is characteristic of Silver-Russell syndrome. Because Grb10 is a signaling protein capable of interacting with tyrosine kinase receptors, we tested genetically whether Grb10 might act downstream of insulin-like growth factor 2, a paternally expressed growth-promoting gene. The result indicates that Grb10 action is essentially independent of insulin-like growth factor 2, providing evidence that imprinting acts on at least two major fetal growth axes in a manner consistent with parent-offspring conflict theory.

Alleles↗