Figure 1.

Ntn5 is expressed in Boundary cap cells (BCC). A dendrogram calculated from the primary amino acid sequences of mouse netrins demonstrates that netrin5 is more similar to netrin1 and netrin3 than is netrin4 (A). Ntn5 expression was assayed by in situ hybridization. Using a riboprobe and tyramide signal amplification, expression was detected at the dorsal root entry zone (DREZ) of the spinal cord (B) and adjacent to the trigeminal ganglia (C) at embryonic day 15.5. By the ViewRNA branched DNA probe technique, expression was verified at the DREZ and detected at the motor exit point (MEP, motor neurons (MNs) labeled for ChAT, E). Ntn5-expressing cells at both locations were Krox20-positive BCC (F,G). Expression at the MEP was strongest between E13.5 and E17.5 (K,L) and was barely detectable at P0 (M). Likewise, labeling at the DREZ peaked between E13.5–E17.5 (H,I) and was diminished by P0 (J). In Ntn1^GT/+ embryos immunostained for βGal—a reporter of Ntn1 expression in these mice—there is no colocalization with Krox20-positive BCC (D). TG, trigeminal ganglion; DH, dorsal horn of the spinal cord; VH, ventral horn. Scale bar is 550 μm in (B,C,E), 300 μm in (F,G), and 400 μm in (D,H–M).