Expression patterns of engrailed -like proteins in the chick embryo

Abstract

The protein products of both of the identified chick engrailed -like ( En ) genes, chick En-1 and chick En-2 , are localized in cells of the developing brain, mandibular arch, spinal cord, dermatome, and ventral limb bud ectoderm, as demonstrated by labeling with the polyclonal antiserum ΑEnhb-1 developed by Davis et al. (Development 111:281–298, 1991). A subpopulation of cephalic neural crest cells is also En -protein-positive. The monoclonal antibody 4D9 recognizes the chick En-2 gene product exclusively (Patel et al.: Cell 58:955–968, 1989; Davis et al., 1991) and colocalizes with chick En-2 mRNA in the developing head region of the chick embryo as shown by in situ hybridization (Gardner et al.: J. Neurosci. Res. 21:426–437, 1988). In the present study we examine the pattern of ΑEnhb-1 and 4D9 localization throughout the chick embryo from the first appearance of antibody (Ab)-positive cells at stage 8 (Hamburger and Hamilton: J. Morphol. 88:49–92, 1951) through stage 28 (1–5.5 days). We compare the localization patterns of the two Abs to each other, as well as to the localization of the monoclonal Ab, HNK-1, which recognizes many neural crest cells, using double-and triple-label fluorescence immunohistochemistry. Most En protein-positive cells in the path of neural crest cell migration are not HNK-1 positive. In detailed examination of ΑEnhb-1 and 4D9 localization, we find previously undetected patterns of En protein localization in the prechordal plate, hindbrain, myotome, ventral body-wall mesoderm, and extraembryonic membranes. Based upon these observations we propose: (1) that En expression in the mesoderm may be induced through interaction with En expressing cells in the neuroectoderm; (2) that En expression in the head mesenchyme is associated with somitomere 4; and (3) that En expression may be involved in epithelial-mesenchymal cell transformations. © 1992 Wiley-Liss, Inc.