Protogenin Facilitates Trunk-to-Tail HOX Code Transition via Modulating GDF11/SMAD2 Signaling in Mammalian Embryos

Vertebral axial patterning is determined during embryogenesis via complicated regulation involving multiple signaling networks. This study revealed that protogenin (Prtg), a member of the immunoglobulin superfamily, is involved in controlling vertebral patterning. Prtg knockout (Prtg-/-) mice exhibited anterior homeotic transformations in their vertebral columns accompanied by significant alternations in the expression of numerous homeobox (Hox) genes. Transcriptomic profiling of Prtg-/- embryos revealed that genes regulated by Prtg play a pivotal role in modulating axial development, displaying prominent associations with the transforming growth factor beta (TGFß) signaling pathway. Additionally, we observed a pronounced reduction in TGFß signaling activity in Prtg-/- embryos, as evidenced by decreased phosphorylated Smad2 (pSmad2) levels within the developing tail region. Furthermore, we introduced human induced pluripotent stem cell-derived presomitic mesoderm-like (hiPSC-PSM) cells as an in vitro model to explore the role of PRTG in somitogenesis, specifically focusing on the collinear expression of HOX genes. Our findings indicate that PRTG knockout in hiPSC-PSM cells results in delayed posterior HOX gene expression. Intriguingly, supplementation with growth differentiation factor 11 (GDF11) successfully rescued the abnormal expression of posterior HOX genes, providing compelling evidence that PRTG's regulation of HOX genes is mediated by the GDF11/SMAD2 signaling pathway. Overall design: Transgenic C57BL/6 mice containing Prtg knockout allele was used in this study. Heterozygous males were mated with heterozygous females and pragnant females were sacrificed to obtain E9.5 embryos. Embryos were dissected between 12th and 13th somite and total RNA from posterior trunks were extracted by Tissue Total RNA Mini Kit (Geneaid) for RNA-seq.