Makiko Meguro

A new imprinted cluster on the human chromosome 7q21-q31, identified by human-mouse monochromosomal hybrids

We have previously established a series of human monochromosomal hybrids containing a single human chromosome of defined parental origin as an in vitro resource for the investigation of human imprinted loci. Using the hybrids with a paternal or maternal human chromosome 7, we determined the allelic expression profiles of 76 ESTs mapped to the human chromosome 7q21-q31. Seven genes/transcripts, including PEG10 which has previously been reported to be imprinted, showed parent-of-origin-specific expression in monochromosomal hybrids. One of the 6 candidate genes/transcripts, i.e., DLX5 was confirmed to be imprinted in normal human lymphoblasts and brain tissues by a polymorphic analysis. Thus, an imprinted domain has been newly defined in the region of human chromosome 7q21-q31 using human-mouse monochromosomal hybrids.

Expression profile of LIT1/KCNQ1OT1 and epigenetic status at the KvDMR1 in colorectal cancers

The human chromosome region 11p15.5 contains a number of maternally and paternally imprinted genes, and the LIT1/KCNQ1OT1 locus acts as an imprinting center in the proximal domain of 11p15.5. Loss of imprinting (LOI) of LIT1 and its correlation with methylation status at a differentially methylated region, the KvDMR1, were investigated in 69 colorectal cancer tissue specimens. LIT1 expression profiles were also examined by RNA‐fluorescence in situ hybridization in 13 colorectal cancer cell lines. In 69 colorectal cancer tissue specimens, LOI of LIT1 was observed in nine of the 17 (53%) informative cases. Moreover, LOI of LIT1 was only observed in tumor samples. In the cell lines, methylation status at the KvDMR1 correlated well with LIT1 expression profiles. Loss of expression of LIT1 also correlated with enrichment of H3 lysine 9 (H3‐K9) dimethylation and reduction of H3 lysine 4 (H3‐K4) dimethylation. Thus, LIT1 expression appears to be controlled by epigenetic modifications at the KvDMR1, although CDKN1C expression, which is considered to be controlled by LIT1, was not associated with epigenetic status at the KvDMR1 in some colorectal cancer cell lines. Therefore, these findings suggest that LOI of LIT1 via epigenetic disruption plays an important role in colorectal carcinogenesis, but it is not necessarily associated with CDKN1C expression. (Cancer Sci 2006; 97: 1147–1154)

Predominant maternal expression of the mouse Atp10c in hippocampus and olfactory bulb

AbstractThe human chromosome 15q11-q13 region is one of the most intriguing imprinted domains, and the abnormalities inherited are associated with neurological disorders including Prader-Willi syndrome (PWS), Angelman syndrome (AS) and autism. Recently we have identified a novel maternally expressed gene, ATP10C, that encodes a putative aminophospholipid translocase within this critical region, 200 kb distal to UBE3A in an imprinted domain on human chromosome 15. ATP10C, with UBE3A, displayed tissue-specific imprinting with predominant expression of the maternal allele in the brain. In this study, we demonstrated that the mouse homologue, Atp10c/pfatp showed tissue-specific maternal expression in the hippocampus and olfactory bulb, which overlapped the region of imprinted Ube3a expression. These data suggest that the imprinted transcript of Atp10c in the specific region of CNS may be associated with neurological disorders including AS and autism.

Loss of Imprinting of Long QT Intronic Transcript 1 in Colorectal Cancer

Loss of imprinting (LOI) of the insulin-like growth factor 2 (IGF2) and H19 genes on human chromosome 11 has been found not only in childhood tumors but also in common adult cancers including colorectal cancer. Recently, a transcript called LIT1 (long QT intronic transcript 1) has been identified within the KvLQT1 locus on chromosome 11. LIT1 is expressed preferentially from the paternal allele and is transcribed in most human tissues. LOI of LIT1 was found in a considerable number of Beckwith-Wiedemann syndrome (BWS) patients, suggesting that it is associated with the etiology of BWS. Since LOI of IGF2 was observed in association with overexpression of IGF2 in colorectal cancer in our previous study, we examined the status of genomic imprinting of LIT1 and H19 in comparison with IGF2 in colorectal cancer. We examined 44 surgically dissected colorectal cancer tissues. Ten of them represented informative cases for LIT1. None of these patients exhibited loss of heterozygosity (LOH) of LIT1, and LOI of LIT1 was observed in 4 of the 10 (40%) informative patients, but not in non-cancerous tissues. Neither LOH nor LOI of H19 was observed. LOI of IGF2 was observed in 4 of 18 (22%) informative patients. These results suggest that LOI of LIT1 is frequently observed in colorectal cancer and may be a useful marker for diagnosis of colorectal cancer.

Calcr, a brain-specific imprinted mouse calcitonin receptor gene in the imprinted cluster of the proximal region of chromosome 6

AbstractExpressed sequence tags (ESTs) in the human chromosome 7q21-q31 region were recently used to screen for allelic expression bias in monochromosomal hybrids retaining a paternal or maternal human chromosome 7. Six candidate imprinted genes were identified. In this study, we investigated parent-of-origin-specific expression profiles of their mouse homologues in the proximal region of chromosome 6. An imprinting analysis, using F1 mice from reciprocal crosses between the B6 and JF strains, demonstrated that the mouse calcitonin receptor gene (Calcr) was expressed preferentially from the maternal allele in brain, whereas no allelic bias was detected in other tissues. Our results indicate that Calcr is imprinted in a tissue-specific manner, with a predominant expression from the maternal allele in the brain.

Epigenetic reprogramming of the human H19 gene in mouse embryonic cells does not erase the primary parental imprint

Genomic imprinting in mammals is thought to result from epigenetic modifications to chromosomes during gametogenesis, which leads to differential allelic expression during development. There is a requirement for an appropriate experimental system to enable the analysis of the mechanisms of genomic imprinting during embryogenesis.

Narrowed abrogation of the Angelman syndrome critical interval on human chromosome 15 does not interfere with epigenotype maintenance in somatic cells.

AbstractHuman chromosome 15q11-q13 involves a striking imprinted gene cluster of more than 2 Mb that is concomitant with multiple neurological disorders manifested by Prader-Willi syndrome (PWS) and Angelman syndrome (AS). PWS and AS patients with imprinting mutation have microdeletions, which share a 4.3 kb short region of overlap (SRO) at the 5′ end of the paternal SNURF-SNRPN gene in PWS, or on the maternal allele, which shares a 880 bp SRO located at the 35 kb upstream of the SNURF-SNRPN promoter in AS. Recent studies have revealed an essential role of PWS-SRO in the postzygotic maintenance of the appropriate epigenotype on the paternal chromosome. For AS-SRO, however, there is insufficient experimental evidence exists to determine the direct functions. Here we show that the complete deletion of AS-SRO does not cause any anomalies of imprinted gene expression or DNA methylation on the mutated human chromosome 15, further supporting the idea that AS-SRO is dispensable for post implantation imprint maintenance. This implies that AS-SRO is not essential for the robust epigenotype preservation in somatic cells.