AUTS2 controls neuronal lineage choice through a novel PRC1-independent complex and BMP inhibition

Abstract

Despite a prominent risk factor for Neurodevelopmental disorders (NDD), it remains unclear how Autism Susceptibility Candidate 2 (AUTS2) controls the neurodevelopmental program. Our studies investigated the role of AUTS2 in neuronal differentiation and discovered that AUTS2, together with WDR68 and SKI, forms a novel protein complex (AWS) specifically in neuronal progenitors and promotes neuronal differentiation through inhibiting BMP signaling. Genomic and biochemical analyses demonstrated that the AWS complex achieves this effect by recruiting the CUL4 E3 ubiquitin ligase complex to mediate poly-ubiquitination and subsequent proteasomal degradation of phosphorylated SMAD1/5/9. Furthermore, using primary cortical neurons, we observed aberrant BMP signaling and dysregulated expression of neuronal genes upon manipulating the AWS complex, indicating that the AWS-CUL4-BMP axis plays a role in regulating neuronal lineage specification in vivo. Thus, our findings uncover a sophisticated cellular signaling network mobilized by a prominent NDD risk factor, presenting multiple potential therapeutic targets for NDD.

AUTS2 Syndrome: Molecular Mechanisms and Model Systems

“…Subsequently, WDR68 was identified as an additional component of the AUTS2-containing ncPRC1 complex ( Wang et al, 2018 ). On the other hand, two groups have reported that AUTS2-FL interacts with ncPRC1, but AUTS2-C does not ( Geng et al, 2021 ; Monderer-Rothkoff et al, 2021 ). In a study of mutations in AUTS2 syndrome, the interaction of AUTS2 with P300 in HEK 293 cells was found to be disrupted by mutations involving the HX repeat ( Liu et al, 2021 ).…”

“…Importantly, the HX repeat encompasses the alternative tss for AUTS2-C, and indeed a small deletion in the HX repeat was found to eliminate expression of AUTS2-C ( Martinez-Delgado et al, 2021 ). Significantly, most of the above-mentioned AUTS2-protein interactions and disruptions were studied in HEK cells after AUTS2 overexpression ( Gao et al, 2014 ; Wang et al, 2018 ; Geng et al, 2021 ), or in yeast two-hybrid assays ( Monderer-Rothkoff et al, 2021 ). Further studies are needed to confirm that AUTS2 interacts with proteins such as PCGF3/5, RING1B, and P300 at physiological levels in cortical neurons in vivo .…”

“…In HEK cells and in mESCs differentiated to radial glia-like neuronal progenitor cells, both AUTS2-FL and AUTS2-C interacted with WDR68 and SKI to form a novel AUTS2-WDR68-SKI (AWS) complex ( Geng et al, 2021 ). The AWS complex recruited CUL4, a ubiquitin E3 ligase, to mediate proteolytic degradation of phosphorylated SMAD1/5/9, and thereby inhibit BMP pathway signaling to promote neuronal differentiation ( Geng et al, 2021 ).…”

“…In HEK cells and in mESCs differentiated to radial glia-like neuronal progenitor cells, both AUTS2-FL and AUTS2-C interacted with WDR68 and SKI to form a novel AUTS2-WDR68-SKI (AWS) complex ( Geng et al, 2021 ). The AWS complex recruited CUL4, a ubiquitin E3 ligase, to mediate proteolytic degradation of phosphorylated SMAD1/5/9, and thereby inhibit BMP pathway signaling to promote neuronal differentiation ( Geng et al, 2021 ). Further studies of this proposed mechanism are needed to evaluate its relevance to cortical neuron differentiation in vivo , since the aforementioned studies were done in cultured HEK cells or mESCs, after overexpression of AUTS2 or proposed interacting molecules.…”

“…Finally, a novel mouse Auts2 allele with conditional excision of exon 9 ( Auts2 del9 ) was recently described ( Geng et al, 2021 ). Excision of exon 9 was reported to deplete both AUTS2-FL and AUTS2-C, although no details of the generation of these mice, nor documentation of the protein depletion, were provided.…”