Fig. 2.
SED1 is expressed in the mammary epithelium during development. (A) SED1 immunoreactivity is seen at the earliest stages of ductal development associated with both luminal and myoepithelial cells. Immunoreactivity increases during development and reaches peak levels at ≈5–6 weeks, when both luminal and myoepithelial cells are embedded in SED1 immunoreactivity (arrowheads denote myoepithelial cells based on nuclear architecture, apposition to the basal lamina, and SMA reactivity). SED1 expression remains stable or decreases slightly until the onset of lactation, when it is abundantly expressed in the secretory acini (1 dpp). No immunoreactivity is seen with preimmune sera (PI). (B) Double-label immunofluorescence in WT glands (+/+) illustrates SED1 immunoreactivity (Alexa Fluor 488, green) associated with both luminal and myoepithelial cells, as seen by colocalization with SMA (Alexa Fluor 594, red) (arrowheads). (C) In situ hybridization confirms SED1 transcription during gland development (5 weeks) and is up-regulated during lactation (1 dpp). Sense probes produced no hybridization. The double layer of hybridization is consistent with SED1 being synthesized by both epithelial cell types. (Scale bars, 0.05 mm in all images.)