Quantitative comparisons of LIF mRNA concentration were possible by normalizing to the constitutively expressed gene cyclophilin. Increased LIF mRNA concentration relative to that of cyclophilin suggests that LIF is transcriptionally regulated in the skunk uterus. However, in the present study it was not possible to determine whether the change in LIF transcript abundance is due to changes in mRNA synthesis or rate of degradation. Regardless of the mechanism of regulation, the increase in uterine concentration of LIF mRNA at the time of early embryo activation was concurrent with the detection of increased LIF protein. Our RT-PCR assay does not discriminate between the matrix-associated and diffusible forms of LIF described by Rathjen and coworkers. antibiotic levaquin
Consequently, it is not known which forms of LIF are produced by the skunk uterus during the periimplantation period. During the early stages of embryo attachment, LIF protein was localized primarily to the lumen of the uterus, indicating that much of it is being secreted. Secretion of LIF has also been demonstrated in human endometrial and stromal cell cultures and in uterine flushings of the human and pig. Once in the uterine lumen, LIF may bind to receptors (LIFRp) located on the blastocyst and on the apical surface of the luminal epithelium in the mouse and human.