Distinct signaling center and progenitor identity dynamics initiate human forebrain patterning

At which developmental stage does the human brain start to differ from other mammals? We uncover human features of telencephalic patterning as early as the fourth post-conception week, comparing the early mouse and human forebrains using single-cell transcriptomics and 3D spatial multi-transcript imaging. In comparison to mice, the human telencephalon is delayed in ventral SHH signaling, accompanied by a human signature of anterior FGF signaling. These observations correlate with a less-resolved patterning and reduced progenitor diversity along the dorsoventral and anteroposterior axes, as well as a human early neurogenic signature. Our complementary approaches reveal a human divergence in allocation of telencephalic progenitor identities, propelled by temporal and qualitative differences in ventro-anterior signals following neural tube closure in the developing forebrain.