Cellular Retinoid-Binding Protein Expression Levels in the Uterus of the Pregnant Rat

To determine the relative levels of expression of each of the proteins during early pregnancy, cytosols were prepared from frozen uteri (3-4 uterine horns were pooled) collected at various times during the periimplantation period. Equal amounts of cytosolic protein from each sample (50 |xg) were separated on SDS-PAGE gels, transferred to a polyvinyl difluoride membrane, and probed with antibodies previously shown to be specific for the binding proteins against which they were generated.

The expression of CRBP increased after Day 1, reaching its highest level at Day 3-4, and then decreased to levels seen at Day 1 (Fig. 1A). CRABP levels decreased to a lower level on Day 2 and Day 3, then increased to higher levels than seen at Day 1 (Fig. IB). The change in expression of CRABP(II) was the most dramatic. It was expressed at its highest level on Day 1 but decreased dramatically by Day 2. A small rebound was apparent on Day 4 and Day 5 (Fig. 1C). These changes in expression level were not quantified because it became clear from the subsequent work that the changes were due to a combination of factors such as disappearance at one site coupled with appearance at a new site, or a change for the same cell type that was region dependent. Thus any change in total uterine content of the binding proteins simply reflected the dynamic nature of retinoid processing during early pregnancy, and no specific conclusions could be drawn from the degree of change. The sites and changes of expression indicated by the Western analysis were examined by immunohistochem-ical localization of the binding proteins for several samples of half uteri representing each day of the periimplantation pregnancy. asthma inhalers
Fig1Spatial and temporal patterns
FIG. 1. Western blot analysis of CRBP (A), CRABP (B), and CRABP(II) (C) in the rat uterus during the periimplantation period. Lanes 1-7, proteins from Days 1 to 7 of pregnancy, respectively.