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H. P. Makarenkova, C. Tsau, R. Meech, E. Boiko; The Homeodomain Transcription Factor Barx2 Is Required for Normal Lacrimal Gland Development and Cooperates With FGF10 in Regulation of Branching Morphogenesis. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4236.
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© ARVO (1962-2015); The Authors (2016-present)
The lacrimal gland (LG) develops through branching morphogenesis and produces secretions that lubricate and protect the ocular surface. Despite the frequency of LG disorders, relatively little is known about regulation of LG development. The goal of our research is to understand the specific role of transcription factor Barx2 and FGF signaling in regulation of LG development and repair.
In this study we have examined the LG development in Barx2 mutant mice by standard histological techniques, in situ hybridization and immunohistochemistry. We used gelatin zymography, and q-RT-PCR to study regulation of matrix metalloproteinase (MMP) expression by FGF10 and Barx2. Mouse Extracellular Matrix and Adhesion Molecules RT²ProfilerTM PCR microarray was used to study specific downstream targets of Barx2.
Barx2 is expressed in the LG epithelium. Loss of Barx2 function led to impaired lacrimal gland morphogenesis. In most cases, lacrimal glands of Barx2-/- mice were vestigial, remained closely associated with the eye, and showed an altered branching pattern. These results, combined with our finding, that absence of Barx2 correlates with decreased expression of MMPs and some other extracellular matrix molecules suggest that degradation of the extracellular matrix is inefficient in Barx2-/- mice. This conclusion is supported by the finding that ectopic expression of Barx2 in the A253 epithelial cell line expression promoted migration of cells through the matrix and increased the expression of MMPs. Moreover, gelatin zymography showed that both Barx2 and FGF10 regulate MMP2 and MMP9 secretion. In addition, Barx2-/- LG epithelial explants showed decreased response to FGF10 in an in vitro migration assay.
The decreased expression of MMPs in Barx2-/- mice may lead to impaired matrix remodeling. Such a defect may alter propagation of the lacrimal bud through the extracellular matrix, resulting in the impaired branch elongation and formation of vestigial LG observed in these mutant mice. In addition to promoting matrix remodeling, Barx2 may have other roles in stimulating epithelial responses to FGFs during LG morphogenesis.
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