The BMP antagonist Gremlin1 contributes to the development of cortical excitatory neurons, motor balance and fear responses

Bone morphogenetic protein (BMP) signaling is required for early forebrain development, however the role of this signaling pathway in later cortical patterning awaits careful mechanistic investigation. How the endogenous modulators of BMP signaling regulate the structural and functional maturation of the developing brain remains unclear. Here we show that expression of the BMP antagonist, Grem1, marks a neuroprogenitor that gives rise to layer Ⅴ and Ⅵ excitatory glutamatergic neurons in the embryonic mouse brain. Lineage tracing of Grem1-expressing cells in the fetal brain was examined by administration of tamoxifen to pregnant Grem1creERT; Rosa26LSLTdtomato mice at 13.5 days post coitum (dpc), followed by collection of embryos later in gestation. In addition, at 14.5 dpc, bulk mRNA seq analysis of differentially expressed transcripts between FACS sorted Grem1 positive and negative cells was performed. We also generated Emx1-cre mediated Grem1 conditional knockout mice (Emx1-Cre;Grem1flox/flox, Grem1Emx1cKO) in which the Grem1 gene was deleted specifically in the dorsal telencephalon. Grem1Emx1cKO animals had reduced cortical thickness, especially layers Ⅴ and Ⅵ. Behavioural tests revealed Grem1Emx1cKO mice have impaired motor balance and fear sensitivity compared to littermate controls. This study has revealed new roles for Grem1 in the structural and functional maturation of the developing cortex.