Abstract
Purpose: :
The purpose of this study was to characterize the natural history of meibomian gland morphogenesis in the mouse.
Methods: :
KC-ZEG bi-transgenic mice that express EGFP driven by the keratocan promoter to label neural crest derived mesenchymal cells and the parental C57Bl/6 control mice were used in this study. Embryonic (E) and post natal (P) mouse pups were obtained at E18.5, P0, P1, P3, P5, P8 and P15. Eyelids were fixed in 2% paraformaldehyde and processed for en bloc immunostaining or standard immunocytochemistry following equilibration in serial sucrose from 15% up to 30%, embedding in OCT and freezing in liquid nitrogen. Tissues sections (10 µm) were then stained with oil red O (ORO) or rabbit antibodies specific for peroxisome proliferator-activated receptor gamma (PPARγ, Abcam ) a marker of lipogenesis to identify meibocyte differentiation. En bloc tissue was counterstained with rhodamine conjugated phalloidin and DAPI to identify cells and nuclei. Samples were then evaluated using a Nikon Eclipse E600 fluorescence microscope or Zeiss 510 Meta laser scanning confocal microscope.
Results: :
Meibomian gland morphogenesis was first detected at E18.5 with the formation of an epithelial placode within the fused lid margin epithelium. Invagination of ORO and PPARγ negative epithelium into the lid was first detected at P0 and P1 in association with condensation of EGFP positive mesenchymal cells that formed a cap over the distal end of the developing gland. By P3 a solid cord of epithelium had extended approximately 275 µm into the lid mesenchym that remained ORO and PPARγ negative and would later form the meibomian gland duct. Both ORO and PPARγ staining were first detected at PN5 associated at the terminus of branch points along the gland and within the internal epithelial cells of the proximal portion of the developing meibomian gland to form the central lumen of the meibomian gland duct. By P15, when the mouse eyelids opened, a patent duct and well developed acini were present.
Conclusions: :
We have demonstrated that Meibomian gland development bears distinct similarities to hair development with the formation of an epithelial placode adjacent to condensed mesenchymal cells of neural crest origin. Furthermore, the adipogenic transcription factor PPARγ is expressed in differentiating meibocytes in association with lipid production beginning at post natal day 5 in the mouse. Meibomian glands appear to be completely formed by the time of eyelid opening.
Keywords: cornea: tears/tear film/dry eye • development