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Updated: Apr 26, 2026

Quantitative PCR-based Assay to Measure Sonic Hedgehog Signaling in Cellular Model of Ciliogenesis
Published on: January 31, 2025
Psip1/Ledgf p75 restrains Hox gene expression by recruiting both trithorax and polycomb group proteins
Madapura M Pradeepa1, Graeme R Grimes2, Gillian C A Taylor2
1MRC Human Genetics Unit, MRC Institute of Genetics and Molecular Medicine at University of Edinburgh, Crewe Road, Edinburgh EH4 2XU, UK Wendy.Bickmore@igmm.ed.ac.uk.
Abstract:
Trithorax and polycomb group proteins are generally thought to antagonize one another. The trithorax family member MLL (myeloid/lymphoid or mixed-lineage leukemia) is presumed to activate Hox expression, counteracting polycomb-mediated repression. PC4 and SF2 interacting protein 1 (PSIP1)/p75, also known as LEDGF, whose PWWP domain binds to H3K36me3, interacts with MLL and tethers MLL fusion proteins to HOXA9 in leukaemias. Here we show, unexpectedly, that Psip1/p75 regulates homeotic genes by recruiting not only MLL complexes, but also the polycomb group protein Bmi1. In Psip1(-/-) cells binding of Mll1/2, Bmi1 and the co-repressor Ctbp1 at Hox loci are all abrogated and Hoxa and Hoxd mRNA expression increased. Our data not only reveal a potential mechanism of action for Psip1 in the regulation of Hox genes but also suggest an unexpected interplay between proteins usually considered as transcriptional activators and repressors.
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