Expression of CXCL12 and CXCR4 in human endometrium; effects of CXCL12 on MMP production by human endometrial cells

BACKGROUND

Although several studies have suggested that CXCL12 and its receptor, CXCR4, may play a role in embryo implantation, there are limited reports of expression of CXCR4 and CXCL12 in human endometrium. The aim of this study was to investigate CXCL12 and CXCR4 expression in human endometrium and to see if CXCL12 could affect matrix metalloproteinase (MMP) production by endometrial stromal and epithelial cells.

METHODS

Quantitative real-time RT-PCR (qRT-PCR) was used to detect the expression of CXCL12 and CXCR4 mRNA in endometrial biopsy samples obtained from fertile women (n = 30). Immunohistochemical analysis was carried out to determine where in the endometrium CXCL12 and CXCR4 were expressed. Primary cell culture followed by qRT-PCR and zymography was used to investigate whether CXCL12 affected MMP-2 and -9 production by endometrial stromal and epithelial cells.

RESULTS

Both CXCL12 and CXCR4 were detected in the endometrium. There was no difference in CXCL12 expression at different times in the cycle, but expression of CXCR4 mRNA was significantly higher in the early proliferative (P < 0.01) compared with late proliferative and secretory phases of the cycle. CXCL12 expression was strongest in the epithelial compartment, and weaker in blood vessel walls. CXCR4 immunostaining was strong in the epithelium and blood vessel walls and weaker in the stroma. CXCL12 (10 and 100 ng/ml) had no effect on mRNA expression or activity of MMP-2 or MMP-9 in either stromal or epithelial cells.

CONCLUSIONS

The results show that the expression of CXCL12 in human endometrium does not alter during the menstrual cycle, while the endometrial expression of its receptor, CXCR4, is highest in the early proliferative phase. In contrast to its effects in other cells, CXCL12 had no effect on MMP-2 or MMP-9 production by endometrial stromal or epithelial cells.

tRNA-rRNA sequence homologies: a model for the origin of a common ancestral molecule, and prospects for its reconstruction

A model is proposed for the early evolution of the coding mechanism. A primordial RNA embodies the functions of today's nucleic acids in a single molecule. The molecule is generated by successive rounds of self-priming and -templating. After proximity is assured by enclosure in a cell, the functions can be partitioned among more efficient specialized molecules. The prediction of sequence homologies in later forms prompted a search for matches between t- and r-RNAs. These are described. Their distributions offer clues to their origins. The existance of overlapping homologies indicates an approach to the reconstruction of an ancestral molecule.

tRNA-rRNA sequence homologies: evidence for a common evolutionary origin?

Many tRNAs of E. coli and yeast contain stretches whose base sequences are similar to those found in their respective rRNAs. The matches are too frequent and extensive to be attributed to coincidence. They are distributed without discernible pattern along and among the RNAs and between the two species. They occur in loops as well as in stems, among both conserved and non-conserved regions. Their distributions suggest that they reflect common ancestral origins rather than common functions, and that they represent true homologies.