Fig. 8. A model describing Bmp7 function in lacrimal gland development. We propose that in the lacrimal gland, through stimulation of mesenchymal proliferation and aggregation, Bmp7 promotes formation of signaling centers and, as a result, branching morphogenesis (A). We also suggest that the pattern of lobe formation in the lacrimal gland can be explained in part by the combined action of Fgf10 and Bmp7 where Fgf10 is a stimulus for bud elongation and Bmp7 for branching (A,B). During the initial 48 hours of lacrimal gland development, we suggest that the primary bud extends and does not branch because the epithelium is exposed only to Fgf10 (A,B, zone A). By contrast, we propose that upon entering the defined region of Bmp7-expressing mesenchyme, epithelium will branch because it is exposed to Bmp7 (A,B, zone C). It is possible that this regulation of branching is mediated not by the absolute presence or absence of Bmp7, but by different Bmp7 levels.