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Alx-4, a transcriptional activator whose expression is restricted to sites of epithelial-mesenchymal interactions
R Hudson1, A Taniguchi-Sidle, K Boras
1Department of Laboratory Medicine and Pathobiology, University of Toronto, Ontario, Canada.
Abstract:
We have recently demonstrated that the retinoblastoma family of negative cell cycle regulators can form complexes with a class of developmental factors which contain paired-like (PL) homeodomains (Wiggan et al. [1998] Oncogene 16:227-236). Our screens led to the isolation of a novel PL-homeodomain protein which had been isolated independently by another group and called Alx-4 (Qu et al. [1997] Development 124:3999-4008). Mice homozygous for a targeted null mutation of Alx-4 have several abnormalities, including preaxial polydactyly, suggesting that Alx-4 plays a role in pattern formation in limb buds. In data that we present here, we show that Alx-4 is expressed in mesenchymal condensations of a diverse group of tissues whose development is dependent on epithelial-mesenchymal interactions, many of which are additionally dependent on expression of the HMG-box-containing protein, LEF-1. Alx-4-expressing tissues include osteoblast precursors of most bones, the dermal papilla of hair and whisker follicles, the dental papilla of teeth, and a subset of mesenchymal cells in pubescent mammary glands. We show further that Alx-4 strongly activates transcription from a promoter containing the homeodomain binding site, P2. Optimal activation requires specific sequences in the N-terminal portion of Alx-4 as well as a proline-rich region downstream of the PL-homeodomain, but not the paired-tail at the C terminus. Taken together, our results demonstrate that Alx-4 is a potent transcriptional activator that is expressed at sites of epithelial-mesenchymal interactions during murine embryonic development.
Insights
Alx-4, a novel paired-like homeodomain protein, is a potent transcriptional activator crucial for embryonic development. It is expressed in tissues undergoing epithelial-mesenchymal interactions, impacting pattern formation in mouse embryos.
Area of Science:
- Developmental Biology
- Molecular Biology
- Genetics
Background:
- Retinoblastoma family proteins interact with paired-like (PL) homeodomain developmental factors.
- Alx-4 is a novel PL-homeodomain protein implicated in embryonic development.
- Alx-4 null mutant mice exhibit abnormalities like preaxial polydactyly, suggesting a role in limb bud pattern formation.
Purpose of the Study:
- To investigate the expression patterns of Alx-4 during murine embryonic development.
- To determine the transcriptional activation potential of Alx-4.
- To identify the functional domains of Alx-4 involved in transcriptional activation.
Main Methods:
- Analysis of Alx-4 expression in various embryonic tissues.
- Creation and analysis of Alx-4 null mutant mice.
- Reporter gene assays to assess transcriptional activation by Alx-4.
Main Results:
- Alx-4 is expressed in mesenchymal condensations of tissues dependent on epithelial-mesenchymal interactions, including osteoblast precursors, dermal papilla, dental papilla, and mammary glands.
- Alx-4 strongly activates transcription from a promoter with a homeodomain binding site (P2).
- Transcriptional activation by Alx-4 requires specific N-terminal sequences and a proline-rich region, but not the C-terminal paired-tail.
Conclusions:
- Alx-4 is a potent transcriptional activator involved in murine embryonic development.
- Alx-4 expression is localized to sites of critical epithelial-mesenchymal interactions.
- These findings highlight Alx-4's role in pattern formation during embryonic development.