Fig. 1. Formation of Cajal-Retzius cells from Msx1⁺ domain of the dorsal telencephalic midline. (A,A') Orientation of sections. (B-D'') Coronal sections of E10.5 embryos. Msx1 was expressed in the prospective choroid plexus region (B). Some Msx1⁺ cells expressed Ngn2 (C-C'', arrowheads) but not DCX (D-D''). (E-M'') Transgenic mice carrying the Msx1 promoter-driven EGFP reporter were examined for lineage tracing of Msx1⁺ cells. At E10.0, EGFP was specifically expressed by Msx1⁺ cells (E-E''). At E10.5, EGFP was expressed in the prospective choroid plexus region (G) like the endogenous Msx1 (F). Subsets of EGFP⁺ cells expressed Ngn2 (H-H'',K-K'', arrowheads), Tuj1 (I-I'',L-L'', arrowheads) and p73 (J-J'',M-M'', arrowheads) at both E10.5 and E11.5, suggesting that some Msx1⁺ cells differentiated into Cajal-Retzius cells. di, diencephalon; tel, telencephalon. Scale bars: 50 µm.