Cohesin mediates Esco2-dependent transcriptional regulation in a zebrafish regenerating fin model of Roberts Syndrome

摘要

Robert syndrome (RBS) and Cornelia de Lange syndrome (CdLS) are human developmental disorders characterized by craniofacial deformities, limb malformation and mental retardation. These birth defects are collectively termed cohesinopathies as both arise from mutations in cohesion genes. CdLS arises due to autosomal dominant mutations or haploinsufficiencies in cohesin subunits (SMC1A,?SMC3?and?RAD21) or cohesin auxiliary factors (NIPBL?and?HDAC8) that result in transcriptional dysregulation of developmental programs. RBS arises due to autosomal recessive mutations in cohesin auxiliary factor?ESCO2, the gene that encodes an N-acetyltransferase which targets the SMC3 subunit of the cohesin complex. The mechanism that underlies RBS, however, remains unknown. A popular model states that RBS arises due to mitotic failure and loss of progenitor stem cells through apoptosis. Previous findings in the zebrafish regenerating fin, however, suggest that Esco2-knockdown results in transcription dysregulation, independent of apoptosis, similar to that observed in CdLS patients. Previously, we used the clinically relevant?CX43?to demonstrate a transcriptional role for Esco2.?CX43?is a gap junction gene conserved among all vertebrates that is required for direct cell-cell communication between adjacent cells such that?cx43?mutations result in oculodentodigital dysplasia. Here, we show that morpholino-mediated knockdown of?smc3?reduces?cx43?expression and perturbs zebrafish bone and tissue regeneration similar to those previously reported for?esco2?knockdown. Also similar to Esco2-dependent phenotypes, Smc3-dependent bone and tissue regeneration defects are rescued by transgenic Cx43 overexpression, suggesting that Smc3 and Esco2 cooperatively act to regulate cx43 transcription. In support of this model, chromatin immunoprecipitation assays reveal that Smc3 binds to a discrete region of the?cx43?promoter, suggesting that Esco2 exerts transcriptional regulation of?cx43?through modification of Smc3 bound to the?cx43?promoter. These findings have the potential to unify RBS and CdLS as transcription-based mechanisms.