Gene expression profiles in the bovine corpus luteum (CL) during the estrous cycle and pregnancy: possible roles of chemokines in regulating CL function during pregnancy

Abstract

To determine functional differences between the corpus luteum (CL) of the estrous cycle and pregnancy in cows, gene expression profiles were compared using a 15 K bovine oligo DNA microarray. In the pregnant CL at days 20-25, 40-45 and 150-160, the expressions of 138, 265 and 455 genes differed by a factor of > 2-fold (P < 0.05) from their expressions in the cyclic CL (days 10-12 of the estrous cycle). Messenger RNA expressions of chemokines (eotaxin, lymphotactin and ENA-78) and their receptors (CCR3, XCR1 and CXCR2) were validated by quantitative real-time PCR. Transcripts of eotaxin were more abundant in the CL at days 40-45 and 150-160 of pregnancy than in the cyclic CL (P < 0.01). In contrast, the mRNA expressions of lymphotactin, ENA-78 and XCR1 were lower in the CL of pregnancy (P < 0.05). Messenger RNAs of CCR3 and CXCR2 were similarly detected both in the cyclic and pregnant CL. Tissue protein levels of eotaxin were significantly higher in the CL at days 150-160 of pregnancy than in the CL at other stages, whereas the lymphotactin protein levels in the CL at days 20-25 of pregnancy were lower (P < 0.05). Immunohistochemical staining showed that CCR3 was expressed in the luteal cells and that XCR1 was expressed in both the luteal cells and endothelial cells. Collectively, the different gene expression profiles may contribute to functional differences between the cyclic and pregnant CL, and chemokines including eotaxin and lymphotactin may regulate CL function during pregnancy in cows.

Fig. 1.

Changes in relative amounts of mRNAs for (A) eotaxin, (B) lymphotactin and (C) ENA-78 and their receptors, (D) CCR3, (E) XCR1 and (F) CXCR2 in the bovine cyclic CL and pregnant CL. Data are means ± SEM for four cows per stage and are expressed as relative ratios of the mRNAs to 18S ribosomal RNA (RN18S1). ^a,b,c Bars without a common letter differ (P < 0.05 or lower).

Fig. 2.

(A) Concentrations of a) eotaxin and b) lymphotactin in the bovine luteal tissues from the cyclic and pregnant stages evaluated by ELISA. Data are means ± SEM for four cows per stage. ^a,b Bars without a common letter differ (P < 0.05 or lower). (B) Localization of a) CCR3 and b) XCR1 in the bovine CL evaluated by immunohistochemistry. Intensive immunoreactivity was observed in luteal cells (black arrowheads) and endothelial cells (white arrowheads). No positive immunoreactivity was observed in the negative control (inserted panels). Scale bar = 50 µm.