Data presents mean values of three independent experiments

homozygotes mutation p<0.01 between WT iPS cells and different mutant iPS cells, respectively. B: Western blot result of dyskerin protein in HEK293T cells showing doxycycline inducible DKC1 shRNA can reduce the dyskerin level to about 1020%. shGFP was used as a control. C: Telomerase activity of HEK293T cells after knocking down of dyskerin protein from B was measured by TRAP assay. The quantitive data, derived by densitometry, are shown. D; Knock down of dyskerin protein can directly decrease the expression PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19666584 of LGR5, WLS and FRZB genes. Two different DKC1 shRNA lines were used in this experiment. The combined results of 3 independent experiments are shown, the error bars show standard deviation. p<0.01. doi:10.1371/journal.pone.0127414.g004 cells from DC patients have been published with some differences in the kinetics of telomere maintenance. Agarwal et al found DKC1 mutant iPS cells have elongated telomeres compared to fibroblast cells, but Winkler et al and Batista et al reported telomere shortening and low TERC expression in TERC, TERT or DKC1 mutated iPS cells, respectively. Here, we generated three different iPS cell lines from X-linked DC patient's fibroblast cells carrying DKC1 A353V, Q31E and L37 mutations and showed that all three lines expressed low TERC RNA compared to WT controls. Telomere maintenance varied between the mutations; Q31E and L37 mutant iPS cells could not elongate telomeres as WT control cells do after reprograming and they maintain the same length as in the corresponding fibroblast. In Chebulinic acid 19667254?dopt=Abstract” title=View Abstract(s)”>PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19667254 A353V iPS cells, the telomere length is much shorter than in the corresponding fibroblast cells suggesting the A353V mutation more severely affects telomerase function. From our study and the others the consensus is that iPS cells recapitulate the effects on telomerase and telomere maintenance seen in DC and thus represent an abundant source of DC cells for further investigation. This is particularly valuable in the case of DC since other cells that can be obtained from patients, fibroblasts and transformed lymphocytes, do not express telomerase. As well as telomere maintenance, dyskerin is essential for the maturation and modification of ribosomal RNA and there is a long-standing controversy concerning the importance of ribosome biogenesis and translation defects in the pathogenesis of DC. Mouse models with complete or partial knockdown of dyskerin, or those with mutations that mimic human pathogenic mutations show delays in ribosome biogenesis and a decrease in the level of pseudouridine in mature rRNA. Reported downstream consequences of these defects are alterations in translation, notably decreased translation of mRNAs that use IRES elements for translation initiation. Our previous work on mouse ES cells with A353V, G402E and 15 mutations strongly suggested mutant dyskerin could cause significant ribosomal defects, including decreased pseudouridine levels in rRNA, delayed maturation of ribosome RNA, decreased expression of H/ACA snoRNA and altered rRNA migration pattern due to secondary structure changes. Other investigators using cells from DC patients failed to show effects on ribosome biogenesis though these cells are scarce and difficult to obtain in reasonable quantities. We reasoned that our iPS cells would be good cells in which to examine the effects of DKC1 mutations on ribosome biogenesis. Surprisingly, we did not find a significant difference between WT and mutant iPS cells in the kinetics of rRNA processing o