Fibrillarin is essential for early development and required for accumulation of an intron-encoded small nucleolar RNA in the mouse.
Fibrillarin, a protein component of C/D box small nucleolar ribonucleoproteins (snoRNPs), directs 2'-O-methylation of rRNA and is also involved in other aspects of rRNA processing. A gene trap screen in embryonic stem (ES) cells resulted in an insertion mutation in the fibrillarin gene. This insertion generated a fusion protein that contained the N-terminal 132 amino acids of fibrillarin fused to a beta-galactosidase-neomycin phosphotransferase reporter. As a result, the N-terminal GAR domain was present in the fusion protein but the methyltransferase-like domain was missing. The ES cell line with the targeted fibrillarin allele was transmitted through the mouse germ line, creating heterozygous animals. Western blot analyses showed a reduction in fibrillarin protein levels in the heterozygous knockout animals. Animals homozygous for the mutation were inviable, and massive apoptosis was observed in early Fibrillarin(-/-) embryos, showing that fibrillarin is essential for development. Fibrillarin(+/-) live-born mice displayed no obvious growth defect, but heterozygous intercrosses revealed a reduced ratio of +/- to +/+ mice, showing that some of the Fibrillarin heterozygous embryos die in utero. Analyses of tissue samples and cultured embryonic fibroblasts showed no discernible alteration in pre-rRNA processing or the level of the U3 snoRNA. However, the level of the intron-encoded box C/D snoRNA U76 was clearly reduced. This suggests a high requirement for snoRNA synthesis during an early stage in development.
Newton
Kathryn
K
MRC Human Genetics Unit, Edinburgh EH4 2XU, United Kingdom.
Petfalski
Elisabeth
E
Tollervey
David
D
Cáceres
Javier F
JF
D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis / Q000235:genetics / Q000502:physiology; D001483:Base Sequence; D002868:Chromosomal Proteins, Non-Histone / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D005314:Embryonic and Fetal Development / Q000235:genetics / Q000502:physiology; D005260:Female; D018507:Gene Expression Regulation, Developmental; D006579:Heterozygote; D007438:Introns; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D010641:Phenotype; D011247:Pregnancy; D012323:RNA Processing, Post-Transcriptional; D020537:RNA, Small Nucleolar / Q000235:genetics* / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism
D002868:Chromosomal Proteins, Non-Histone; D020537:RNA, Small Nucleolar; D011993:Recombinant Fusion Proteins; C047458:fibrillarin