Shwachman-Diamond syndrome (SDS) (OMIM #260400) is a rare inherited bone marrow failure syndrome (IBMFS) that is primarily characterized by neutropenia and exocrine pancreatic insufficiency. Seventy-five to ninety percent of patients have compound heterozygous loss-of-function mutations in the Shwachman-Bodian-Diamond syndrome (SBDS) gene. Using trio whole-exome sequencing (WES) in an SBDS-negative SDS family and candidate gene sequencing in additional SBDS-negative SDS cases or molecularly undiagnosed IBMFS cases, we identified 3 independent patients, each of whom carried a de novo missense variant in SRP54 (encoding signal recognition particle 54 kDa). These 3 patients shared congenital neutropenia linked with various other SDS phenotypes. 3D protein modeling revealed that the 3 variants affect highly conserved amino acids within the GTPase domain of the protein that are critical for GTP and receptor binding. Indeed, we observed that the GTPase activity of the mutated proteins was impaired. The level of SRP54 mRNA in the bone marrow was 3.6-fold lower in patients with SRP54-mutations than in healthy controls. Profound reductions in neutrophil counts and chemotaxis as well as a diminished exocrine pancreas size in a SRP54-knockdown zebrafish model faithfully recapitulated the human phenotype. In conclusion, autosomal dominant mutations in SRP54, a key member of the cotranslation protein-targeting pathway, lead to syndromic neutropenia with a Shwachman-Diamond-like phenotype.

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The TEAD (1-4) transcription factors comprise the conserved TEA/ATTS DNA-binding domain recognising the MCAT element in the promoters of muscle-specific genes. Despite extensive genetic analysis, the function of TEAD factors in muscle differentiation has proved elusive due to redundancy among the family members. Expression of the TEA/ATTS DNA-binding domain that acts as a dominant negative repressor of TEAD factors in C2C12 myoblasts inhibits their differentiation, whereas selective shRNA knockdown of TEAD4 results in abnormal differentiation characterised by the formation of shortened myotubes. Chromatin immunoprecipitation coupled to array hybridisation shows that TEAD4 occupies 867 promoters including those of myogenic miRNAs. We show that TEAD factors directly induce Myogenin, CDKN1A and Caveolin 3 expression to promote myoblast differentiation. RNA-seq identifies a set of genes whose expression is strongly reduced upon TEAD4 knockdown among which are structural and regulatory proteins and those required for the unfolded protein response. In contrast, TEAD4 represses expression of the growth factor CTGF (connective tissue growth factor) to promote differentiation. Together these results show that TEAD factor activity is essential for normal C2C12 cell differentiation and suggest a role for TEAD4 in regulating expression of the unfolded protein response genes. The TEAD transcription factors make a highly conserved family of 4 DNA-binding proteins 1,2 containing the TEA (Yeast (TEC-1), Aspergillus nidulans (AbaA) and Drosophilla (scalloped))/ATTS (Aspergillus nidulans (AbaA), Yeast (TEC-1), human TEF1, and Drosophilla (scalloped)) DNA-binding domain (DBD). 3,4 The TEA domain comprises a three-helix bundle with a homeodomain fold and binds a consensus MCAT (5 0 -CATTCCA/ T-3 0 ) element originally defined as the GT-II motif of the simian virus 40 (SV40) enhancer. 5 Mammalian TEADs are widely expressed with prominent expression in the nervous system and muscle. In-vitro, cell-based, knockout and transgenic studies have addressed the role of TEAD factors in regulation of muscle-expressed genes. 6-8 Cardiac troponin T, myosin, heavy polypeptide 7, cardiac muscle, beta (b-MHC) and Myocardin, have functional MCAT motifs in their regulatory regions. 2 Stimulation of a1-adrenergic signalling has been shown to induce cardiac hypertrophy and activate transcription of the b-MHC and skeletal a-actin genes in an MCAT-and TEAD-dependent manner in cultured neonatal rat cardiomyocytes. 9 Cardiac muscle-specific overexpression of TEAD4 in transgenic mice has been shown to induce arhythmias in vivo. 8 TEAD4 is specifically expressed in developing skeletal muscle in mouse embryos. 1 Chromatin immunoprecipitation-array hybridization (ChIP-chip) showed that TEAD4 is a direct target of the MYOD1 and MYOG transcription factors in C2C12 cells. 10 Although TEAD4 upregulation by MYOD1 and MYOG during differentiation is thought to activate transcription of muscle structural genes, mouse knockouts do not show any evident role for TEAD4 i...