Figure 1. USF up-regulates breast apelin expression during pregnancy and lactation in the rat. A) Northern blot analysis shows that breast apelin expression increases during pregnancy and lactation when compared with cyclic rats. Three rats per group are shown. B) Mean ± SEM of densitometric readings of apelin expression levels in cyclic, 6 d pregnant (6 d preg), 21 d preg, 3 d lactating (3 d lac), and 16 d lact. n = 5. Apelin expression levels are normalized to 18S rRNA. C) EMSAs show that binding of a consensus USF oligonucleotide to breast nuclear extract is greatest during early pregnancy and early lactation in the rat. EMSAs were done using a ³²P-labeled consensus USF oligonucleotide and breast nuclear extracts (10 µg) harvested from cyclic (lanes 1–3), 6 d preg (lanes 4–6), 21 d preg (lanes 7, 8), 3 d lac (lanes 9, 10) and 16 d lac (lanes 11–13) female rats. Two DNA-protein complexes were formed (arrows). Western blotting analysis of protein extracts used in EMSAs indicates consistent histone H3 levels in all nuclear protein extracts. *P < 0.01 vs. cyclic; P < 0.05 vs. 3 d lac; = P < 0.05 vs. 6 d preg, 3 d lac, and 16 d lac.