Wiskott-Aldrich syndrome protein forms nuclear condensates and regulates alternative splicing

Abstract

The diverse functions of WASP, the deficiency of which causes Wiskott-Aldrich syndrome (WAS), remain poorly defined. We generated three isogenic WAS models using patient induced pluripotent stem cells and genome editing. These models recapitulated WAS phenotypes and revealed that WASP deficiency causes an upregulation of numerous RNA splicing factors and widespread altered splicing. Loss of WASP binding to splicing factor gene promoters frequently leads to aberrant epigenetic activation. WASP interacts with dozens of nuclear speckle constituents and constrains SRSF2 mobility. Using an optogenetic system, we showed that WASP forms phase-separated condensates that encompasses SRSF2, nascent RNA and active Pol II. The role of WASP in gene body condensates is corroborated by ChIPseq and RIPseq. Together our data reveal that WASP is a nexus regulator of RNA splicing that controls the transcription of splicing factors epigenetically and the dynamics of the splicing machinery through liquid-liquid phase separation.

Biomolecular condensates: Formation mechanisms, biological functions, and therapeutic targets

“… 137 Moreover, the condensates formed by WASP, SRSF2, RNA, and Pol II are able to control RNA transcription and splicing, and defects in condensate formation lead to Wiskott‐Aldrich syndrome. 184 …”

“…The condensates of STING were able to constrained TBK1 to prevent excessive activation of innate immunity, while microtubule inhibitors could hinder the generation of these condensates and increase the production of type I interferon in DNA virus‐infected cells 137 . Moreover, the condensates formed by WASP, SRSF2, RNA, and Pol II are able to control RNA transcription and splicing, and defects in condensate formation lead to Wiskott‐Aldrich syndrome 184 …”

“…137 Moreover, the condensates formed by WASP, SRSF2, RNA, and Pol II are able to control RNA transcription and splicing, and defects in condensate formation lead to Wiskott-Aldrich syndrome. 184 In adaptive immunity, GRB2 and SOS1 can form condensates, which bind to T cell adaptor protein LAT and promote thymus cell development. 141 PLCγ1 is also able to directly cross-link LAT through its two SH2 domains to form condensates that protect LAT from dephosphorylation by CD45 and promote LAT-dependent ERK activation and SLP76 phosphorylation.…”

Correcting inborn errors of immunity: From viral mediated gene addition to gene editing

“…Wiskott-Aldrich Syndrome (WAS) is a severe X-linked PID caused by mutations in the WAS gene which encodes the WAS protein (WASp), a key regulator of cytoskeleton reorganization also involved in signaling transduction in all hematopoietic cells [193] . Recently, WASp roles in the nucleus have been described [194] , [195] , [196] , highlighting its multifaceted roles and explaining the complexity of clinical manifestations. The absence of WASp impairs both innate and adaptive immunity as well as platelet number and function resulting in the full-blown WAS characterized by immunodeficiency, thrombocytopenia, eczema and increased risk of autoimmune manifestations and malignancies [197] .…”

Wiskott-Aldrich Syndrome Protein Regulates Nucleolar Organization and Function in Innate Immune Response

“…This suggests that WASP has other roles beyond regulating actin nucleation. Studies from our group and others have demonstrated the WASP functions in multiple biological processes , including regulating message RNA (mRNA) alternative splicing 5 , maintaining genome stability 6,7,8 , nuclear translocation of NFAT2 and NF-κB (RelA) 9 , and TH1 lineage commitment 10 .…”