Figure 4. Changes in Hox and reporter protein expression after Cre-mediated recombination.

(a–f) Immunohistochemistry using anti-Hoxc6, anti-Hoxc8, and anti-Hoxc9 antibodies in cross-sectioned e12.5 caudal cervical level spinal cord. Many Hoxc6⁺ and Hoxc8⁺, but few Hoxc9⁺ cells are present in Hoxc8->c9^F/+-GFP embryos (a–c). Several remaining Hoxc8⁺ cells along with increased Hoxc9 and decreased Hoxc6 expression are visible in the Hoxc8->c9^F/F-GFP; Nescre spinal cord (d–f).

(g–h) Immunohistochemistry using anti-Hoxc8 and anti-Isl1 antibodies in cross-sectioned caudal cervical level e12.5 spinal cord. There is no overlap between Isl1 and Hoxc8 expression in a Hoxc8^F/F-GFP;Islcre (h) embryo compared to the control littermate (g). Hoxc8 expression is also absent in LMCl MNs (marked by white dashed lines) where Isl1 is only expressed transiently (h).

(i) Cross-sectioned spinal cord from an e12.5 Hoxc8^F/F-GFP;Islcre embryo showing high levels of GFP expression revealed by an anti-GFP antibody in dI3 interneurons (white arrow) and in MNs lacking Hoxc8 expression, while low levels of GFP expression are observed in Hoxc8⁺ neurons. GFP expression is also visible in the axons. Scale bars=100µm.

(j–k) High levels of β-galactosidase activity are observed in the spinal cord of an e11.5 Hoxc8->c9^F/F-LacZ;Islcre embryo (k) compares to the low-level β-galactosidase activity present in the spinal cord and mesoderm in their Hoxc8->c9^F/+ littermates (i). Red dotted lines mark the position of the forelimbs. Scale bar=1 mm.