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Study finds a link between the action of a protein in the nucleus and the cytoplasm

In a recent study, researchers from the Institute for Stem Cell Biology and Regenerative Medicine (InStem), the National Centre for Biological Sciences (NCBS), Bengaluru, and the University of Edinburgh, UK, have deciphered an exciting role of a human protein commonly found in the brain. The protein, called Fragile-X mental retardation protein (FMRP), plays a vital role in the development of cognitive functions.

Until now, it was known that FMRP, found in the liquid inside the cells, bound with ribosomes and regulate the production of some vital proteins. The loss of this protein leads to a genetic condition called Fragile X syndrome, leading to learning and cognitive disabilities. However, it is now known that this protein is also found in the nucleus of the cells. So, what is it doing in the nucleus?  This question got researchers behind the current study thinking.

The researchers found that FMRP in the nucleus interacts with specific RNA molecules called small nucleolar RNAs (snoRNAs), some of which are known to modify the ribosomal RNA by adding a methyl group to them. “Our work, for the first time, defines an interaction of an RNA binding protein, FMRP, with a specific subset of C/D box snoRNAs”, say the authors of the study published in the journal iScience and partially supported by the Department of Biotechnology.

“This interaction may have an influence in regulating rRNA methylation in humans. In the absence of FMRP, methylation was altered”, they note.

The addition of methyl group to ribosomal RNAs has biological significance since it contributes to heterogeneity or variations in the ribosomes. This variation might lead to different rates of synthesis of proteins in the cell. Since FMRPs also interact with ribosomes, can they recognise the methylations in ribosomes? “We found that FMRP recognizes ribosomes carrying specific methylation patterns on the rRNA”, say the authors.

The findings of the study indicate a potential link between the function of this protein in the nucleus, and in the cytoplasm of a cell, which might help in the regulation of protein synthesis.

“Our results identify a nuclear function of FMRP and imply that it can integrate translation regulation between the nucleus and cytoplasm,” conclude the authors.