Faculty Bibliography

Proximal-distal outgrowth of the vertebrate limb bud is regulated by the apical ectodermal ridge (AER), which forms at an invariant position along the dorsal-ventral (D/V) axis of the embryo. We have studied the genetic and cellular events that regulate AER formation in the mouse. In contrast to implications from previous studies in chick, we identified two distinct lineage boundaries in mouse ectoderm prior to limb bud outgrowth using a Cre/loxP-based fate-mapping approach and a novel retroviral cell-labeling technique. One border is transient and at the limit of expression of the ventral gene En1, which corresponds to the D/V midline of the AER, and the second border corresponds to the dorsal AER margin. Labeling of AER precursors using an inducible Cre showed that not all cells that initially express AER genes form the AER, indicating that signaling is required to maintain an AER phenotype. Misexpression of En1 at moderate levels specifically in the dorsal AER of transgenic mice was found to produce dorsally shifted AER fragments, whereas high levels of En1 abolished AER formation. In both cases, the dorsal gene Wnt7a was repressed in cells adjacent to the En1-expressing cells, demonstrating that signaling regulated by EN1 occurs across the D/V border. Finally, fate mapping of AER domains in these mutants showed that En1 plays a part in positioning and maintaining the two lineage borders

BACKGROUND: An inadequate understanding of the complex morphologic characteristics of human filiform papillae has hampered the histopathological characterization of disorders affecting tongue keratinization. To better define the 3-dimensional cytoarchitecture of tongue epithelium, we performed detailed immunohistochemical analyses of normal and black hairy tongue tissues using a panel of antikeratin antibodies. OBSERVATIONS: The dome-shaped base of the human filiform papilla (primary papilla) is surmounted by 3 to 8 elongated structures (secondary papillae). These secondary papillae are composed of a central column of epithelial cells expressing hair-type keratins and an outer rim of cells expressing skin-type keratins. The epithelium overlying the primary papillae and between the individual primary papillae express esophageal-type keratins. In black hairy tongue disease, there is a marked retention of secondary papillary cells expressing hair-type keratins. CONCLUSIONS: Using a panel of antikeratin probes, we define the precise topographical localization of cell populations undergoing 3 distinct differentiation programs in dorsal tongue epithelium. Comparative analyses of black hairy tongue specimens indicate that defective desquamation of the cells in the central column of filiform papillae results in the formation of highly elongated, cornified spines or, 'hairs'--the hallmark of this disease

The Engrailed-1 gene, En1, a murine homologue of the Drosophila homeobox gene engrailed (en), is required for midbrain and cerebellum development and dorsal/ventral patterning of the limbs. In Drosophila, en is involved in regulating a number of key patterning processes including segmentation of the epidermis. An important question is whether, during evolution, the biochemical properties of En proteins have been conserved, revealing a common underlying molecular mechanism to their diverse developmental activities. To address this question, we have replaced the coding sequences of En1 with Drosophila en. Mice expressing Drosophila en in place of En1 have a near complete rescue of the lethal En1 mutant brain defect and most skeletal abnormalities. In contrast, expression of Drosophila en in the embryonic limbs of En1 mutants does not lead to repression of Wnt7a in the embryonic ventral ectoderm or full rescue of the embryonic dorsal/ventral patterning defects. Furthermore, neither En2 nor en rescue the postnatal limb abnormalities that develop in rare En1 null mutants that survive. These studies demonstrate that the biochemical activity utilized in mouse to mediate brain development has been retained by Engrailed proteins across the phyla, and indicate that during evolution vertebrate En proteins have acquired two unique functions during embryonic and postnatal limb development and that only En1 can function postnatally

The DAM family of genes has a high degree of homology with MAGE, both in nucleotide sequence and in neoplastic tissue-specific expression. This study describes, for the first time, the identification of CTLs specific for a peptide epitope encoded by DAM genes. A human leukocyte antigen (HLA)-A2-restricted CTL clone was raised against a peptide, D10/6-271, encoded by codons 271-279 in the DAM cDNA. The corresponding peptide in the MAGE-3 sequence, M3-271, has been shown previously to be a natural T-cell epitope for HLA-A2-restricted CTLs recognizing the MAGE-3 protein. The D10/6-271-specific CTL clone required approximately 3 nM exogenous peptide for half-maximal lysis of target cells and was able to specifically recognize endogenous DAM antigen on HLA-A2+ melanoma cells infected with a vaccinia vector recombinant for gene DAM-6. These data suggest that DAM genes might encode a new group of tumor-specific antigens useful for the design of specific antitumor vaccines