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

Abstract

Murine lacrimal, harderian and meibomian glands develop from the prospective conjunctival and eyelid epithelia and produce secretions that lubricate and protect the ocular surface. Sox9 expression localizes to the presumptive conjunctival epithelium as early as E11.5 and is detected in the lacrimal and harderian glands as they form. Conditional deletion showed that Sox9 is required for the development of the lacrimal and harderian glands and contributes to the formation of the meibomian glands. Sox9 regulates the expression of Sox10 to promote the formation of secretory acinar lobes in the lacrimal gland. Sox9 and FGF signaling were required for the expression of cartilageassociated extracellular matrix components during early stage lacrimal gland development. Fgfr2 deletion in the ocular surface epithelium reduced Sox9 and eliminated Sox10 expression. Sox9 deletion from the ectoderm did not affect Fgf10 expression in the adjacent mesenchyme or Fgfr2 expression in the epithelium, but appeared to reduce FGF signaling. Sox9 heterozygotes showed a haploinsufficient phenotype, in which the exorbital branch of the lacrimal gland was absent in most cases. However, enhancement of epithelial FGF signaling by expression of a constitutively active FGF receptor only partially rescued the lacrimal gland defects in Sox9 heterozygotes, suggesting a crucial role of Sox9, downstream of FGF signaling, in regulating lacrimal gland branching and differentiation.

Defining epithelial cell dynamics and lineage relationships in the developing lacrimal gland

“…We first assessed the expression of the acinar/secretory cell markers SOX10, AQP5 and MIST1 at each time point. Although SOX10 has been previously reported to be localized to the end buds of early lacrimal glands (Chen et al, 2014), we did not detect robust nuclear expression of SOX10 protein at E16 despite our qPCR analysis, indicating the presence of transcripts (compare Fig. 3A with Fig.…”

“…Our single cell and immunofluorescent analysis suggest a lineage relationship between acinar and myoepithelial cells, where SOX10 + cells may give rise to the acinar or myoepithelial lineage, or to both. In support of this differentiation capacity, deletion of Sox10 in the lacrimal gland not only impaired acinar cell development but also resulted in absent myoepithelial cells (Chen et al, 2014). Thus, SOX10 is required for the development of myoepithelial cells in addition to acinar cells.…”

“…We prioritized three genes, Sox10, Aqp5 and Mist1 (Bhlha15 -Mouse Genome Informatics), which were previously associated with acinar cells in the lacrimal gland and other glandular organs, to evaluate acinar cell differentiation. SOX10 is a transcription factor enriched in end buds of developing lacrimal glands where it acts downstream of FGF10 and SOX9 to promote acinar cell formation (Chen et al, 2014). In adult murine lacrimal glands, AQP5, a water channel involved in fluid secretion, and MIST1, a transcriptional regulator of the secretory program, label acinar cells, but their developmental expression patterns are unknown (Ishida et al, 1997;Pin et al, 2000Pin et al, , 2001.…”

Sin3a regulates epithelial progenitor cell fate during lung development

“…In contrast, Sox9 expression demarks distal epithelial progenitors and a subpopulation of mesodermal cells associated with proximal lung endoderm (Chen et al, 2014;Rawlins et al, 2009;Rockich et al, 2013). To assess further the molecular effects of Sin3a LOF on lung branching morphogenesis, immunofluorescence co-staining of Sox2, Sox9 and the epithelial adherens junction marker E-cadherin (cadherin 1) was performed on lung sections from E12.5 Sin3a f/f mutant and Sin3a f/+ littermate control embryos.…”

Lacrimal Gland Inflammation Deregulates Extracellular Matrix Remodeling and Alters Molecular Signature of Epithelial Stem/Progenitor Cells

“…58 Sox9 controls the expression of heparan sulfate-synthesizing enzymes (HSSE), which are required for the synthesis and function of heparan sulfate (HS), to promote FGF and other growth factors signaling and LG morphogenesis. 61 Other factors with decreased expression in MRL/lpr and NOD LGs were Iroquois homeobox protein-4 (Irx4; MRL/lpr LG, 2.1-fold increase, P ¼ 0.004942; NOD LGs, 2-fold decrease, P ¼ 0.00045), mesenchymally expressed forkhead box P2 (Foxp2; MRL/lpr LGs, 3.6-fold decrease, P ¼ 0.00017; NOD LGs, 1.8-fold decrease, P ¼ 0.04716), nuclear receptor subfamily 2 (Nr2f2; MRL/lpr LGs, 3.7-fold decrease, P ¼ 0.003041; NOD LG, 2.2-fold decrease, P ¼ 0.042417) and Wilms tumor 1 homolog (Wt1; MRL/lpr LGs, 2.2-fold decrease, P ¼ 0.000001; NOD LG, 2.4-fold decrease, P ¼ 0.000001).…”