Mouse Alx3: an aritaless-like homeobox gene expressed during embryogenesis in ectomesenchyme and lateral plate mesoderm

Mouse Alx3 is a homeobox gene that is related to the Drosophila aristaless gene and to a group of vertebrate genes including Prx1, Prx2, Cart1, and Alx4. The protein encoded contains a diverged variant of a conserved peptide sequence present near the carboxyl terminus of at least 15 different paired-class-homeodomain proteins. Alx3 is expressed in mouse embryos from 8 days of gestation onward in a characteristic pattern, predominantly in neural crest-derived mesenchyme and in lateral plate mesoderm. We detected prominent expression in frontonasal head mesenchyme and in the first and second pharyngeal arches and some of their derivatives. High expression was also seen in the tail and in many derivatives of the lateral plate mesoderm including the limbs, the body wall, and the genital tubercle. aristaless-related genes like Alx3, Cart1, and Prx2 are expressed in overlapping proximodistal patterns in the pharyngeal arches. Similar, but more lateral patterns have been described for the Distal-less-related (Dlx) genes. Intriguingly, expression and to some extent function of aristaless and Distal-less in Drosophila also have overlapping as well as complementary aspects. Alx3 was localized to chromosome 3, near the droopy-ear (de) mutation. Key Words: homeobox gene; pharyngeal arches; skeletogenesis; neural-crest-derived mesenchyme; lateral plate mesoderm; limb development; in situ hybridization; mouse embryology; proximodistal patterning; aristaless; Cart1.