Figure 4. Anterior-median-foxQ2-cluster contributes to the central brain primordium.

Double-immunohistochemistry visualizes the EGFP (green) derived from the foxQ2-5’-line and acTub (magenta) which marks axonal projections – neuraxis anterior is up. (A–A’) At NS13, the first brain commissure marked by acTub appears (white arrowhead in A’). The cell bodies of the anterior-median-foxQ2-cluster are located around this commissure but do not yet project into it. A few weakly stained cells closely attached to the commissure are not Tc-FoxQ2 protein positive (asterisk in A’). (B–B’) At NS14, projections within the brain commissure become visible but have not yet reached the midline (white arrowhead in B). One Tc-FoxQ2 positive NPC is recognized by its morphology and position (hatched circle in B’). (B) and (B’) are not the same embryo but from the same developmental stage. (C–E) At NS15, at least three brain commissures are marked by the anterior-median-foxQ2-cluster: One in the circumesophageal commissure (white arrowhead in E), and two commissures within the central brain primordium (white arrowheads in D). The anterior-median-foxQ2-cluster produces more cells at this stage. (C’–E’) acTub marked brain commissures expand into many fascicles and increase in size. 6–7 axon bundles emanating from the anterior-median-foxQ2-cluster separately join this midline brain primordium (one of them marked by an arrow in C’).

Figure 4—figure supplement 1. Tc-foxQ2 cell clusters are surrounded by glial sheets.

A cross of the foxQ2-5’-line (green) with the glia-line (Koniszewski et al., 2016); magenta) was imaged. (A–A’’) Most of the cells of the anterior-median-foxQ2-cluster are within one glia sheet (white arrowheads, dashed line). The medial-most cells which show comparably weak EGFP signal are surround by another glia sheet (open arrowheads, dashed line). (B–B’’) The anterior-lateral-foxQ2-lineage is surrounded by one glia sheet (orange arrowheads, dashed line).