Figure 1

Embryonic Tabby SMGs are developmentally-delayed. E13 Tabby (TA) SMG (A) has achieved the Initial Bud stage, consisting of a single end bulb. In contrast, E13 wildtype (WT) glands (B) are characterized by cleft formation in the end bud and the formation of a few branches, indicating that it has achieved the Late Initial Bud Stage. The Pseudoglandular stage, composed of a network of epithelial branches and end buds (b), is seen in E14 WT (D) and E15 Tabby (E) SMGs. The presence of ductal lumina (arrows) indicates that the E15 WT (F) and E16 Tabby (G) SMGs have achieved the Canalicular stage. The presence of distinct lumina surrounded by cuboidal epithelia (black arrowhead) in some, but not all, terminal end buds indicates that E16 WT (H) and E17 Tabby (I) SMGs have achieved the Early Terminal Bud stage. By E18, differences in branching morphogenesis and glandular maturation are seen between E18 WT (L) and Tabby (K) glands. Note that the E18 Tabby glands (K) are smaller and exhibits fewer branches than E18 WT glands (L); its branching morphogenesis appears similar to that seen in E17 WT (J) glands. However, the observation of distinct proacinar lumina surrounded by a single layer of cuboidal epithelium (blue arrowhead) and continuity between ductal and proacinar lumina in both E18 Tabby (K) and WT (L) glands (i.e. Late Terminal Bud stage) indicates the similarity in E18 Tabby and WT maturation. Bar: A-D, 40 μm; E-L, 30 μm.