Kye-Yoon Park

Characterization of human embryonic stem cell lines by the International Stem Cell Initiative

The International Stem Cell Initiative characterized 59 human embryonic stem cell lines from 17 laboratories worldwide. Despite diverse genotypes and different techniques used for derivation and maintenance, all lines exhibited similar expression patterns for several markers of human embryonic stem cells. They expressed the glycolipid antigens SSEA3 and SSEA4, the keratan sulfate antigens TRA-1-60, TRA-1-81, GCTM2 and GCT343, and the protein antigens CD9, Thy1 (also known as CD90), tissue-nonspecific alkaline phosphatase and class 1 HLA, as well as the strongly developmentally regulated genes NANOG, POU5F1 (formerly known as OCT4), TDGF1, DNMT3B, GABRB3 and GDF3. Nevertheless, the lines were not identical: differences in expression of several lineage markers were evident, and several imprinted genes showed generally similar allele-specific expression patterns, but some gene-dependent variation was observed. Also, some female lines expressed readily detectable levels of XIST whereas others did not. No significant contamination of the lines with mycoplasma, bacteria or cytopathic viruses was detected.

Missense mutations in desmin associated with familial cardiac and skeletal myopathy.

Desmin-related myopathy (OMIM 601419) is a familial disorder characterized by skeletal muscle weakness associated with cardiac conduction blocks, arrhythmias and restrictive heart failure, and by intracytoplasmic accumulation of desmin-reactive deposits in cardiac and skeletal muscle cells. The underlying molecular mechanisms are unknown. Involvement of the desmin gene (DES) has been excluded in three families diagnosed with desmin-related myopathy. We report two new families with desmin-related cardioskeletal myopathy associated with mutations in the highly conserved carboxy-terminal end of the desmin rod domain. A heterozygous A337P mutation was identified in a family with an adult-onset skeletal myopathy and mild cardiac involvement. Compound heterozygosity for two other mutations, A360P and N393I, was detected in a second family characterized by childhood-onset aggressive course of cardiac and skeletal myopathy.

Analysis of the H19ICR insulator

ABSTRACT Transcriptional insulators are specialized cis-acting elements that protect promoters from inappropriate activation by distal enhancers. The H19 imprinting control region (ICR) functions as a CTCF-dependent, methylation-sensitive transcriptional insulator. We analyzed several insertional mutations and demonstrate that the ICR can function as a methylation-regulated maternal chromosome-specific insulator in novel chromosomal contexts. We used chromosome conformation capture and chromatin immunoprecipitation assays to investigate the configuration of cis-acting elements at these several insertion sites. By comparing maternal and paternal organizations on wild-type and mutant chromosomes, we hoped to identify mechanisms for ICR insulator function. We found that promoter and enhancer elements invariably associate to form DNA loop domains at transcriptionally active loci. Conversely, active insulators always prevent these promoter-enhancer interactions. Instead, the ICR insulator forms novel loop domains by associating with the blocked promoters and enhancers. We propose that these associations are fundamental to insulator function.

Progressive skeletal myopathy, a phenotypic variant of desmin myopathy associated with desmin mutations

Desmin myopathy is a familial or sporadic disorder characterized by the presence of desmin mutations that cause skeletal muscle weakness associated with cardiac conduction block, arrhythmia and heart failure. Distinctive histopathologic features include intracytoplasmic accumulation of desmin-reactive deposits and electron-dense granular aggregates in skeletal and cardiac muscle cells. We describe two families with features of adult-onset slowly progressive skeletal myopathy without cardiomyopathy. N342D point mutation was present in the desmin helical rod domain in patients of family 1, and I451M mutation was found in the non-helical tail domain in patients of family 2. Of interest, the same I451M mutation has previously been reported in patients with cardiomyopathy and no signs of skeletal myopathy. Some carriers of the I451M mutation did not develop any disease, suggesting incomplete penetrance. Expression studies demonstrated inability of the N342D mutant desmin to form cellular filamentous network, confirming the pathogenic role of this mutation, but the network was not affected by the tail-domain I451M mutation. Progressive skeletal myopathy is a rare phenotypic variant of desmin myopathy allelic to the more frequent cardio-skeletal form.

Contribution of Hepatic Lineage Stage-Specific Donor Memory to the Differential Potential of Induced Mouse Pluripotent Stem Cells

Recent studies suggested that induced pluripotent stem cells (iPSCs) retain a residual donor cell gene expression, which may impact their capacity to differentiate into cell of origin. Here, we addressed a contribution of a lineage stage‐specific donor cell memory in modulating the functional properties of iPSCs. iPSCs were generated from hepatic lineage cells at an early (hepatoblast‐derived, HB‐iPSCs) and end stage (adult hepatocyte, AH‐iPSCs) of hepatocyte differentiation as well as from mouse embryonic fibroblasts (MEFs‐iPSCs) using a lentiviral vector encoding four pluripotency‐inducing factors Oct4, Sox2, Klf4, and c‐Myc. All resulting iPSC lines acquired iPSCs phenotype as judged by the accepted criteria including morphology, expression of pluripotency markers, silencing of transducing factors, capacity of multilineage differentiation in teratoma assay, and normal diploid karyotype. However, HB‐iPSCs were more efficient in directed differentiation toward hepatocytic lineage as compared to AH‐iPSCs, MEF‐iPSCs, or mouse embryonic stem cells (mESCs). Extensive comparative transcriptome analyses of the early passage iPSCs, donor cells, and mESCs revealed that despite global similarities in gene expression patterns between generated iPSCs and mESCs, HB‐iPSCs retained a transcriptional memory (seven upregulated and 17 downregulated genes) typical of the original cells. Continuous passaging of HB‐iPSCs erased most of these differences including a superior capacity for hepatic redifferentiation. These results suggest that retention of lineage stage‐specific donor memory in iPSCs may facilitate differentiation into donor cell type. The identified gene set may help to improve hepatic differentiation for therapeutic applications and contribute to the better understanding of liver development. STEM CELLS 2012;30:997–1007

A series of West European patients with severe cardiac and skeletal myopathy associated with a de novo R406W mutation in desmin

Abstract.Desminopathy is a familial or sporadic cardiac and skeletal muscular dystrophy associated with mutations in desmin. We have previously characterized a de novo desmin R406W mutation in a patient of European origin with early onset muscle weakness in the lower extremities and atrioventricular conduction block requiring a permanent pacemaker. The disease relentlessly progressed resulting in severe incapacity within 5 years after onset. We have now identified three other patients with early onset rapidly progressive cardiac and skeletal myopathy caused by this same desmin R406W mutation. The mutation was present in each studied patient, but not in their parents or other unaffected family members, indicating that the mutation in all four cases was generated de novo. The patients’ mutationcarrying chromosomes showed no similarity, suggesting that the R406W mutation has occurred independently. These observations strongly confirm that the de novo R406W desmin mutation is the genetic basis for early-onset cardiac and skeletal myopathy in patients with sporadic disease and indicate that desmin position 406 is a hot spot for spontaneous mutations. The high pathogenic potential of this mutation can be explained by its location in the highly conserved YRKLLEGEE motif at the C-terminal end of the 2B helix that has a critical role in the process of desmin filament assembly.

Sporadic cardiac and skeletal myopathy caused by a de novo desmin mutation

Desmin myopathy is a familial or sporadic disorder characterized by intracytoplasmic accumulation of desmin in the muscle cells. We and others have previously identified desmin gene mutations in patients with familial myopathy, but close to 45% of the patients do not report previous family history of the disease. The present study was conducted to determine the cause of desmin myopathy in a sporadic patient presenting with symmetrical muscle weakness and atrophy combined with atrioventricular conduction block requiring a permanent pacemaker. A novel heterozygous R406W mutation in the desmin gene was identified by sequencing cDNA and genomic DNA. Expression of a construct containing the patients mutant desmin cDNA in SW13 (vim‐) cells demonstrated a high pathogenic potential of the R406W mutation. This mutation was not found in the patients father, mother or sister by sequencing and restriction analysis. Testing with five microsatellite markers and four intragenic single nucleotide polymorphisms excluded alternative paternity. Haplotype analysis indicates that the patients father was germ‐line mosaic for the desmin mutation. We conclude that de novo mutations in the desmin gene may be the cause of sporadic forms of desmin‐related cardiac and skeletal myopathy.

Progressive muscular atrophy variant of familial amyotrophic lateral sclerosis (PMA/ALS)

Twelve cases of adult-onset progressive muscular atrophy variant of amyotrophic lateral sclerosis (PMA/ALS) were studied in a small rural population of 1500 in the Republic of Belarus (former Soviet Union). The patients were members of three apparently related kindreds, each showing autosomal dominant pattern of disease inheritance. The average age at clinical onset ranged from 26 to 57 years (mean, 40 years). Each patient suffered from skeletal muscle weakness and wasting, starting in the limbs and spreading to the trunk and neck, with very limited bulbar and no upper motor neuron involvement. Death from respiratory failure occurred from 13 to 48 months (mean, 28 months) after first symptoms. Dramatically decreased number of spinal motor neurons was the most characteristic neuropathologic feature in two autopsied cases. Most of the remaining degenerating neurons contained intracytoplasmic hyaline inclusion bodies. A D101N mutation in exon 4 of the SOD1 gene was identified in a PMA/ALS patient and in one of her three unaffected children. Our data support the view that some subtypes of familial ALS associated with SOD1 mutations may present as PMA. Diagnostic criteria of ALS should be accordingly modified to include the PMA variant of familial ALS.

The H19 Differentially Methylated Region Marks the Parental Origin of a Heterologous Locus without Gametic DNA Methylation

ABSTRACT Igf2 and H19 are coordinately regulated imprinted genes physically linked on the distal end of mouse chromosome 7. Genetic analyses demonstrate that the differentially methylated region (DMR) upstream of the H19 gene is necessary for three distinct functions: transcriptional insulation of the maternal Igf2 allele, transcriptional silencing of paternal H19 allele, and marking of the parental origin of the two chromosomes. To test the sufficiency of the DMR for the third function, we inserted DMR at two heterologous positions in the genome, downstream of H19 and at the alpha-fetoprotein locus on chromosome 5. Our results demonstrate that the DMR alone is sufficient to act as a mark of parental origin. Moreover, this activity is not dependent on germ line differences in DMR methylation. Thus, the DMR can mark its parental origin by a mechanism independent of its own DNA methylation.

Regulation and expression of the ATP-binding cassette transporter ABCG2 in human embryonic stem cells.

The expression and function of several multidrug transporters (including ABCB1 and ABCG2) have been studied in human cancer cells and in mouse and human adult stem cells. However, the expression of ABCG2 in human embryonic stem cells (hESCs) remains unclear. Limited and contradictory results in the literature from two research groups have raised questions regarding its expression and function. In this study, we used quantitative real‐time PCR, Northern blots, whole genome RNA sequencing, Western blots, and immunofluorescence microscopy to study ABCG2 expression in hESCs. We found that full‐length ABCG2 mRNA transcripts are expressed in undifferentiated hESC lines. However, ABCG2 protein was undetectable even under embryoid body differentiation or cytotoxic drug induction. Moreover, surface ABCG2 protein was coexpressed with the differentiation marker stage‐specific embryonic antigen‐1 of hESCs, following constant BMP‐4 signaling at days 4 and 6. This expression was tightly correlated with the downregulation of two microRNAs (miRNAs) (i.e., hsa‐miR‐519c and hsa‐miR‐520h). Transfection of miRNA mimics and inhibitors of these two miRNAs confirmed their direct involvement in the regulation ABCG2 translation. Our findings clarify the controversy regarding the expression of the ABCG2 gene and also provide new insights into translational control of the expression of membrane transporter mRNAs by miRNAs in hESCs. STEM Cells2012;30:2175–2187