The FGFR1 gene encodes fibroblast growth factor receptor 1 (FGFR1), a pivotal transmembrane receptor tyrosine kinase widely expressed across diverse cell types, including epithelial, mesenchymal, and neuronal lineages, playing fundamental roles in development, angiogenesis, cell proliferation, differentiation, and migration through activation of intracellular signaling cascades like MAPK/ERK, PI3K/AKT, and STAT ^[1]. Aberrant FGFR1 expression or mutations are associated with developmental syndromes and various cancers, driving tumor growth, metastasis, and therapeutic resistance; its expression is tightly regulated by diverse cellular signals ^[2]. A key splice isoform is FGFR1c, predominantly expressed in epithelial cells and characterized by a specific extracellular immunoglobulin-like domain III, conferring high-affinity binding to a subset of FGF ligands crucial for epithelial-mesenchymal interactions during development and adult tissue homeostasis ^[3]. Dysregulation of FGFR1c signaling is implicated in the pathogenesis of cancers such as breast, prostate, and lung carcinomas, contributing to tumor initiation, progression, angiogenesis, and potentially therapy resistance, highlighting the importance of understanding isoform-specific functions for targeted therapeutic interventions ^[3-4].

B6-hFGFR1c mice are humanized models generated by gene editing technology, in which the p.22R to partial intron 2 of the mouse Fgfr1 gene was replaced in situ with p.22R to 376E from the coding sequence of the human FGFR1 gene, p.377I to 823X from the coding sequence of the mouse Fgfr1 gene, and the 3'UTR of the mouse Fgfr1 gene. This model can be used to study the pathological mechanisms and therapeutic methods of cancers, metabolic diseases such as obesity, diabetes, and metabolic-associated steatohepatitis (MASH), as well as the screening and development of FGFR1c-targeted drugs, and preclinical efficacy and safety evaluations.