RESUMEN
Twisted gastrulation (TWSG1) is an evolutionarily conserved secreted glycoprotein which controls signaling by Bone Morphogenetic Proteins (BMPs). TWSG1 binds BMPs and their antagonist Chordin to control BMP signaling during embryonic development, kidney regeneration and cancer. We report crystal structures of TWSG1 alone and in complex with a BMP ligand, Growth Differentiation Factor 5. TWSG1 is composed of two distinct, disulfide-rich domains. The TWSG1 N-terminal domain occupies the BMP type 1 receptor binding site on BMPs, whereas the C-terminal domain binds to a Chordin family member. We show that TWSG1 inhibits BMP function in cellular signaling assays and mouse colon organoids. This inhibitory function is abolished in a TWSG1 mutant that cannot bind BMPs. The same mutation in the Drosophila TWSG1 ortholog Tsg fails to mediate BMP gradient formation required for dorsal-ventral axis patterning of the early embryo. Our studies reveal the evolutionarily conserved mechanism of BMP signaling inhibition by TWSG1.
Asunto(s)
Proteínas Morfogenéticas Óseas , Transducción de Señal , Animales , Proteínas Morfogenéticas Óseas/metabolismo , Proteínas Morfogenéticas Óseas/genética , Ratones , Humanos , Proteínas de Drosophila/metabolismo , Proteínas de Drosophila/genética , Proteínas de Drosophila/química , Glicoproteínas/metabolismo , Glicoproteínas/genética , Péptidos y Proteínas de Señalización Intercelular/metabolismo , Péptidos y Proteínas de Señalización Intercelular/genética , Sitios de Unión , Dominios Proteicos , Unión Proteica , Organoides/metabolismo , Organoides/embriología , Células HEK293 , Gastrulación/genética , Mutación , Cristalografía por Rayos X , Drosophila melanogaster/embriología , Drosophila melanogaster/metabolismo , Drosophila melanogaster/genética , ProteínasRESUMEN
The gastrointestinal (GI) tract is complex and consists of multiple organs with unique functions. Rare gene variants can cause congenital malformations of the human GI tract, although the molecular basis of these has been poorly studied. We identified a patient with compound-heterozygous variants in RFX6 presenting with duodenal malrotation and atresia, implicating RFX6 in development of the proximal intestine. To identify how mutations in RFX6 impact intestinal patterning and function, we derived induced pluripotent stem cells from this patient to generate human intestinal organoids (HIOs). We identified that the duodenal HIOs and human tissues had mixed regional identity, with gastric and ileal features. CRISPR-mediated correction of RFX6 restored duodenal identity. We then used gain- and loss-of-function and transcriptomic approaches in HIOs and Xenopus embryos to identify that PDX1 is a downstream transcriptional target of RFX6 required for duodenal development. However, RFX6 had additional PDX1-independent transcriptional targets involving multiple components of signaling pathways that are required for establishing early regional identity in the GI tract. In summary, we have identified RFX6 as a key regulator in intestinal patterning that acts by regulating transcriptional and signaling pathways.
