Splicing: when « minor » means « of the most importance »

Description

Abstract Splicing is a well-known process that consists in the removal from pre-messenger RNAs of intronic sequences recognized thanks to their consensus splice-sites by a large ribonucleoproteic complex, the spliceosome. The spliceosome is composed of 5 small nuclear RNAs (snRNAs) linked to proteins, called small nuclear ribonucleoproteins (snRNPs), and a large number of additional protein factors and complexes. There are two types of spliceosomes and two types of introns in most organisms, a fact mostly known by splicing specialists: the major introns, the “classical ones”, and the minor introns, so-called as they represent <1% of the total number of introns in most species. Their number differ widely though, with the champion being the slime mold with >20.000 minor introns, versus only 19 in Drosophila and none in C. elegans and S. cerevisiae. In humans, mice and zebrafish, ~850 minor introns are found in ~750 genes among which – a largely ignored fact – some genes that play major roles in diseases such as PTEN, STK11, BRAF (cancer), and XPO7, CUL1, SETD1A as well as all the CACNA and SCN genes (neurological and mental disorders).

The aim of our research project is to unravel the role played by minor intron splicing in gene expression regulation and to understand what goes wrong when this mechanism is impaired, as happens in patients with mutations in U4atac, a component of the minor spliceosome. Indeed, several severe overlapping developmental syndromes (associating microcephaly, intellectual disability, growth retardation, immunodeficiency, bone dysplasia, …) are due to biallelic mutations in RNU4ATAC, the gene for U4atac.

I will present our most recent results, that provide the first pathophysiological mechanism for explaining RNU4ATACassociated syndromes, and reveal an unexpected link between minor and major splicing.

Khatri D*, Putoux A*, Cologne A, Kaltenbach S, Besson A, Bertiaux E, Guguin J, Fendler A, Dupont MA, Benoit-Pilven C, Qebibo L, Ahmed-Elie S, Audebert S, Blanc P, Rambaud T, Castelle M, Cornen G, Grotto S, Guët A, Guibaud L, Michot C, Odent S, Ruaud L, Sacaze E, Hamel V, Bordonné R, Leutenegger AL, Edery P, Burglen L, Attie-Bitach T, Mazoyer S*, Delous M*. Deficiency of the minor spliceosome component U4atac snRNA secondarily results in ciliary defects in human and zebrafish. PNAS, 2023, 120(9):e2102569120.

Benoit-Pilven C*, Besson A*, Putoux A, Benetollo C, Saccaro C, Guguin J, Sala G, Cologne A, Delous M, Lesca G, Padgett RA, Leutenegger AL, Lacroix V, Edery P*, Mazoyer S*. Clinical interpretation of variants identified in RNU4ATAC, a non-coding spliceosomal gene. PLoS ONE, 2020, 15(7):e0235655.

Cologne A, Benoit-Pilven C, Besson A, Putoux A, Campan-Fournier A, Bober MB, de Die-Smulders CEM, Paulussen ADC, Pinson L, Toutain A, Roifman C, Leutenegger AL*, Mazoyer S*, Edery P*, Lacroix V*. New insights into minor splicing – A transcriptomic analysis of cells derived from TALS patients. RNA, 2019, 25(9), 1130-1149.