The Treacher Collins syndrome (TCOF1) gene product is involved in pre-rRNA methylation

Abstract

Treacher Collins syndrome (TCS) is characterized by defects in craniofacial development, which results from mutations in the TCOF1 gene. TCOF1 encodes the nucleolar phosphoprotein treacle, which interacts with upstream binding factor (UBF) and affects transcription of the ribosomal DNA gene. The present study shows participation of treacle in the 2'-O-methylation of pre-rRNA. Antisense-mediated down-regulation of treacle expression in Xenopus laevis oocytes reduced 2'-O-methylation of pre-rRNA. Analysis of RNA isolated from wild-type and Tcof1+/- heterozygous mice embryos from strains that exhibit a lethal phenotype showed significant reduction in 2'-O-methylation at nucleotide C463 of 18S rRNA. The level of pseudouridylation of U1642 of 18S rRNA from the same RNA samples was not affected suggesting specificity. There is no significant difference in rRNA methylation between wild-type and heterozygous embryos of DBA x BALB/c mice, which have no obvious craniofacial phenotype. The function of treacle in pre-rRNA methylation is most likely mediated by its direct physical interaction with NOP56, a component of the ribonucleoprotein methylation complex. Although treacle co-localizes with UBF throughout mitosis, it co-localizes with NOP56 and fibrillarin, a putative methyl transferase, only during telophase when rDNA gene transcription and pre-rRNA methylation are known to commence. These observations suggest that treacle might link RNA polymerase I-catalyzed transcription and post-transcriptional modification of pre-rRNA. We hypothesize that haploinsufficiency of treacle in TCS patients results in inhibition of production of properly modified mature rRNA in addition to inhibition of rDNA gene transcription, which consequently affects proliferation and proper differentiation of specific embryonic cells during development.

Recruitment of factors linking transcription and processing of pre-rRNA to NOR chromatin is UBF-dependent and occurs independent of transcription in human cells

“…Recruitment occurs independent of transcription, the underlying DNA sequence, and nucleolar context, but is strictly UBF-dependent. We also show that TCOF1, a nucleolar protein that has links with both transcription and methylation of rRNA (Hayano et al 2003;Valdez et al 2004;Gonzales et al 2005), and Nopp140, a chaperone for box H/ACA snoRNPs (Meier 2005), are both also recruited to ribosomal gene chromatin independent of transcription. These results highlight the importance of the specialized chromatin structure associated with extensive UBF binding in coordinating ribosome biogenesis.…”

Treacher Collins syndrome: a clinical and molecular study based on a large series of patients

“…[20][21][22] Bowman et al 8 also described five large deletions in TCOF1 in patients with typical TCS, although the full extent of each deletion was not known because they involved either the first or last exon. In this series we identified four intragenic microdeletions within TCOF1 in patients with typical TCS and two large deletions in 5q32 encompassing TCOF1 and neighboring genes in patients with TCS and ID.…”

New bioinformatic tools for analysis of nucleotide modifications in eukaryotic rRNA

“…In addition to addressing issues of modification effects, the new tools will be valuable in studies of how snoRNP function interfaces with rRNA and ribosome synthesis. In the context of human health, defects in snoRNP components have been linked thus far to three human diseases: cartilage-hair hypoplasia, dyskeratosis congenita, and Prader-Willi syndrome (Ridanpaa et al 2001;Fatica and Tollervey 2003;Ruggero et al 2003;Mochizuki et al 2004;Gonzales et al 2005;Meier 2005;Kishore and Stamm 2006;Yoon et al 2006).…”