Comparison of embryonic samples (E18) vs. adult (34 weeks old) lacrimal gland transcriptome

As an element of the lacrimal apparatus, the lacrimal gland (LG) produces the aqueous part of the tear film, which protects the eye surface. Therefore, a defective LG can lead to serious eyesight impairment. Up to now, little is known about LG morphogenesis and subsequent maturation. In this study, we delineated elements of the cellular and molecular events involved in LG formation by using three epithelial markers, namely aSMA, Krt14 andKrt19. While aSMA marked a restricted epithelial population of the terminal end buds (TEBs) in the forming LG, Krt14 was found in the whole embryonic LG epithelial basal cell layer. Interestingly, Krt19 specifically labelled the presumptive ductal domain and subsequently, the luminal cell layer. By combining these markers, the Fucci reporter mouse strain and genetic fate mapping of the Krt14+ population, we demonstrated that LG epithelium expansion is fueled by a patterned cell proliferation, and to a lesser extent by epithelial reorganization and possible mesenchymal-to-epithelial transition. We pointed out that this epithelial reorganization, which is associated with apoptosis, regulated the lumen formation. Finally, we showed that the Notch signalling inhibition prevented the ductal identity from setting, and leads to a LG covered by ectopic TEBs. Taken together our results bring a deeper understanding on LG morphogenesis, epithelial domain identity, and organ expansion. 6 samples were analysed, 3 embryonic samples (biological triplicates, E18) and 3 adult samples (biological triplicates, 34wks old). Embryonic samples were composed of at least 10 LGs (5 individuals) pooled together. Samples were collected for RNA extraction and hybridization on Affymetrix microarrays (MTA1).