Dysregulation of cotranscriptional alternative splicing underlies CHARGE syndrome

Abstract

CHARGE syndrome-which stands for coloboma of the eye, heart defects, atresia of choanae, retardation of growth/development, genital abnormalities, and ear anomalies-is a severe developmental disorder with wide phenotypic variability, caused mainly by mutations in (chromodomain helicase DNA-binding protein 7), known to encode a chromatin remodeler. The genetic lesions responsible for mutation-negative cases are unknown, at least in part because the pathogenic mechanisms underlying CHARGE syndrome remain poorly defined. Here, we report the characterization of a mouse model for mutation-negative cases of CHARGE syndrome generated by insertional mutagenesis of (family with sequence similarity 172, member A). We show that Fam172a plays a key role in the regulation of cotranscriptional alternative splicing, notably by interacting with Ago2 (Argonaute-2) and Chd7. Validation studies in a human cohort allow us to propose that dysregulation of cotranscriptional alternative splicing is a unifying pathogenic mechanism for both mutation-positive and mutation-negative cases. We also present evidence that such splicing defects can be corrected in vitro by acute rapamycin treatment.

Congenital heart defects in CHARGE: The molecular role of CHD7 and effects on cardiac phenotype and clinical outcomes

“…Downstream Semaphorin and Robo pathways are critical to neural crest development and migration and may be involved in CHD7 ‐negative CHARGE syndrome (S R Lalani et al, ; Liu, Guo, et al, ; Schulz et al, ; Ufartes et al, ). Additionally, there is also evidence that the disruption of Fam172a, which interacts with CHD7 and Argo2, can affect alternative splicing in neural crest cells and lead to a CHARGE phenotype (Bélanger et al, ), with neural crest cells being particularly sensitive to disruption of splicing machinery (Bérubé‐Simard & Pilon, ). However, not all aspects of CHARGE can be related to the role of CHD7 on neural crest development.…”

Molecular dissection of CHARGE syndrome highlights the vulnerability of neural crest cells to problems with alternative splicing and other transcription-related processes

“…In the Toupee mouse model of CHARGE syndrome [22], mutagenic transgene sequences are inserted in the last intron of Fam172a, generating a hypomorphic allele that negatively affects almost every aspect of NCC ontology (migration, proliferation, survival and differentiation). Yet, we found that Fam172a expression is not restricted to this cell lineage, being instead almost ubiquitously expressed in embryonic day (e)8.5 to e12.5 embryos.…”

“…In a sustained and concerted effort to identify neurocristopathy-associated genes [18][19][20][21], we recently generated a mouse model for CHD7 mutation-negative CHARGE syndrome, by random insertional mutagenesis of the poorly characterized gene Fam172a [22]. We found that Fam172a codes for a new Ago2-binding protein that seems to be essential for stabilizing proteinprotein interactions at the chromatin-spliceosome interface.…”

Developmental processes regulate craniofacial variation in disease and evolution

“…Both these molecular processes lead to protein synthesis, which is crucial for neural crest cell survival. Image modeled after Hallgrimsson et al , Belanger et al , and Calo et al …”

“…Both these molecular processes lead to protein synthesis, which is crucial for neural crest cell survival. Image modeled after Hallgrimsson et al 2014, Belanger et al 2018, and Calo et al 2018 of NCCs appear to be particularly sensitive to perturbation, which may imply a high demand for protein synthesis in these cells. However, rescue of NCC survival by down-regulation of p53 in Tcofdeficient mice occurs independently of ribosome biogenesis (Jones et al, 2008).…”