Kinesin-mediated membrane trafficking is a fundamental cellular process, but its developmental relevance is little understood. Here we show that the kinesin-3 motor KIF16B/Rab14 complex acts in biosynthetic Golgi-to-endosome traffic of the fibroblast growth factor receptor (FGFR) during early embryonic development. Kif16b(-/-) mouse embryos failed in developing epiblast and primitive endoderm lineages and died in the peri-implantation stage, similar to previously reported FGFR2 knockout embryos. KIF16B associated directly with the Rab14-GTP adaptor on FGFR-containing vesicles and transported them toward the plasma membrane. To examine whether the nucleotide state of Rab14 serves as a switch for transport, we performed Rab14-GDP overexpression. This dominant negative approach reproduced the whole putative sequence of KIF16B or FGFR2 deficiency: impairment in FGFR transport, FGF signaling, basement membrane assembly by the primitive endoderm lineage, and epiblast development. These data provide one of the first pieces of genetic evidence that microtubule-based membrane trafficking directly promotes early development.
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