Endometrial osteopontin, a ligand of β3-integrin, is maximally expressed around the time of the “implantation window”  Michael von Wolff, M.D., Thomas Strowitzki, M.D., Veronika Becker, Claudia Zepf, Siamak Tabibzadeh, M.D., Christian J Thaler, M.D.  Fertility and Sterility  Volume 76, Issue 4, Pages 775-781 (October 2001) DOI: 10.1016/S0015-0282(01)02015-5

FIGURE 1 Osteopontin mRNA expression in total endometrium throughout the menstrual cycle. The expression of osteopontin and the housekeeping genes L32 and GAPDH were examined by RNase protection assay in normal subjects. Probes and positive controls were generated by nested reverse transcriptase polymerase chain reaction and by unilateral polymerase chain reaction. The relative optical density values of the mRNA bands were normalized to the relative optical density of L32 and GAPDH. A representative mRNA expression profile is shown under each diagram, and the corresponding mRNA expression of L32 and GAPDH are shown at the bottom. A two-fold increase of the relative optical density values corresponded, on average, to a 1.8-fold increase of the specific mRNA. Osteopontin mRNA expression increased during the secretory phase with a significant 5–10 fold increase in the mid and late secretory phases. von Wolff. Osteopontin and β3-integrin. Fertil Steril 2001. Fertility and Sterility 2001 76, 775-781DOI: (10.1016/S0015-0282(01)02015-5)

FIGURE 2 Endometrial epithelial, stromal, and leukocyte (CD45) cell fractions were purified by mechanical dissociation, collagenase digestion, filtration, and antibody-coated magnetic beads. Four to five endometrial samples were assigned to each phase of the menstrual cycle. Osteopontin mRNA expression was analyzed by RNase protection assay in duplicates. The relative optical density values of the mRNA bands were normalized to the relative optical densities of L32 and GAPDH bands. Mean relative optical density of each cell fraction is shown in the diagram. The diagram shows that the mRNA increase of osteopontin mRNA in the secretory phase as demonstrated in Fig. 1 was mainly due to an mRNA increase in epithelial cells and to some extent in leukocytes. Osteopontin mRNA expression in stromal cells was very low. von Wolff. Osteopontin and β3-integrin. Fertil Steril 2001. Fertility and Sterility 2001 76, 775-781DOI: (10.1016/S0015-0282(01)02015-5)

FIGURE 3 Immunostaining of osteopontin in human endometrium throughout the menstrual cycle. Staining for osteopontin was negative in the proliferative and early secretory phase (A) and increased in the endometrial glandular (B, arrows) and luminal (D, arrows) epithelium in the mid and late secretory phases. Staining in individual glands was not uniform. Some cells within the glands showed much higher expression for osteopontin (B and C, arrows). Stroma did not stain for osteopontin throughout the cycle. Sections from the secretory phase showed strong staining of single leukocytes (E, arrow). (A, B, D: ×250; E: ×350; C: ×650.) Control staining with goat IgG revealed staining intensity as found in the proliferative phase (A). von Wolff. Osteopontin and β3-integrin. Fertil Steril 2001. Fertility and Sterility 2001 76, 775-781DOI: (10.1016/S0015-0282(01)02015-5)

FIGURE 4 Concentration of osteopontin in uterine secretions in the proliferative and secretory phases of the menstrual cycle. Uterine secretions were collected from the uterine cavity from individuals undergoing hysterectomy by use of a device used for intrauterine cell collection. Five to 10 μL of uterine secretions were diluted in 500 mL phosphate-buffered saline. Analysis was performed by ELISA-kits, designed to recognize native osteopontin. Osteopontin concentrations in diluted uterine secretions increased significantly in the secretory phase. von Wolff. Osteopontin and β3-integrin. Fertil Steril 2001. Fertility and Sterility 2001 76, 775-781DOI: (10.1016/S0015-0282(01)02015-5)