Barx2 and Fgf10 regulate ocular glands branching morphogenesis by controlling extracellular matrix remodeling

Abstract

SUMMARYThe lacrimal gland (LG) develops through branching morphogenesis and produces secretions, including tears, that lubricate and protect the ocular surface. Despite the prevalence of LG disorders such as dry eye, relatively little is known about the regulation of LG development. In this study, we show that the homeobox transcription factor Barx2 is highly expressed in conjunctival epithelium, eyelids and ocular [lacrimal, harderian (HG), and meibomian (MG)] glands and is necessary for normal ocular gland and eyelid development. Barx2 -/-mice show defective LG morphogenesis, absence of the HG, and defects in MG and eyelid fusion. Ex vivo antisense assays confirm the requirement for Barx2 in LG bud elongation and branching. Gene expression profiles reveal decreased expression of several adhesion and matrix remodeling molecules in Barx2 -/-LGs. In culture, Barx2 regulates expression of matrix metalloproteinases (MMPs) and epithelial cell migration through the extracellular matrix. Fibroblast growth factors are crucial regulators of LG development and we show that Barx2 is required for Fgf10-induced LG bud elongation and that both Barx2 and Fgf10 cooperate in the regulation of MMPs. Together, these data suggest a mechanism for the effects of loss of Barx2 on ocular gland development. Intriguingly, salivary glands that also express a high level of Barx2 develop normally in Barx2 -/-mice and do not show altered levels of MMPs. Thus, the function of Barx2 is specific to ocular gland development. Based on our data, we propose a functional network involving Barx2, Fgf10 and MMPs that plays an essential role in regulating branching morphogenesis of the ocular glands.

FGF signaling activates a Sox9-Sox10 pathway for the formation and branching morphogenesis of mouse ocular glands

“…Sox9 could also be detected in the retina, retinal pigmented epithelium and the choroid. The murine lacrimal gland begins to form at E13.5 as a projection from the temporal conjunctival epithelium into the surrounding mesenchyme, and the harderian glands originate by a similar process from the nasal part of the conjunctival epithelium at E15.5 (Tsau et al, 2011). At E14.5, Sox9 was expressed in the nuclei of conjunctival and primary lacrimal bud epithelial cells (Fig.…”

“…Lacrimal and harderian gland development begins on embryonic day (E) 13.5 and 15.5, respectively, when Fgf10 in the periocular mesenchyme interacts with fibroblast growth factor receptor 2b (Fgfr2b) in the ectoderm to induce bud outgrowth Makarenkova et al, 2000;Tsau et al, 2011;Qu et al, 2012).…”

“…Small eye (Sey) mice with a mutation in one copy of Pax6 have vestigial lacrimal glands . Barx2 and Fgf10 regulate ocular gland branching morphogenesis by controlling the expression of matrix metalloproteinases (MMPs) and epithelial cell migration through the ECM (Tsau et al, 2011). Bmp7 is required for the formation of mesenchymal condensations and branching of the lacrimal gland (Dean et al, 2004).…”

Requirement of Fatty Acid Transport Protein 4 for Development, Maturation, and Function of Sebaceous Glands in a Mouse Model of Ichthyosis Prematurity Syndrome

“…Meibomian glands originate from the fused eyelid margin at the late fetal stage (12). Studies of mutant and transgenic mice have shown that tumor necrosis factor receptor-associated factor 6 (5), C/EBP␣ and -␤ (6), ectodysplasin-A receptor signaling (13), bone morphogenetic protein signaling (14,15), homeodomain transcription factor BARX2 (16), and kruppel-like factor 5 (17) are important for meibomian gland development. In contrast, SCD1 is important for meibum production (3,8).…”

Defective eyelid leading edge cell migration in C57BL/6-corneal opacity mice with an “eye open at birth” phenotype

“…The Mtap1B (52.9 cM) gene regulates microtubular recombination. Furthermore, Mtap1B knockout mice developed blindness due to retinopathy (Meixner et al, 2000;Ma et al, 2003;Tsau et al, 2011). RT-PCR and sequencing analysis were used to confirm mutations in Fgf10 ( Figure 7A and B), Plk2 (data not shown), and Mtap1B ( Figure 7F and G) genes, all of which are involved in eyelid development in B6-Co mice.…”