Colony-stimulating factor-1 in conceptus and uterine tissues in pigs

Colony-stimulating factor-1 (CSF-1), a growth factor for cells of monocyte/macrophage lineages, is produced by uterine and placental tissues in humans and mice and may stimulate placental growth and development. The present study characterized CSF-1 mRNA and protein expressed by porcine uterine, conceptus, allantochorion, and fetal tissues at various stages of pregnancy. A human CSF-1 cDNA and an anti-human CSF-1 monoclonal antibody were utilized to examine CSF-1 mRNA and protein. Northern blot analyses detected mRNA transcripts of 3.6-5.1 kb in pig tissues. A 4.0-kb transcript was common to all tissues examined. Endometrial CSF-1 mRNA increased (p < 0.05) as pregnancy proceeded, with highest levels at term, and was temporally associated with concentrations of estrogen (E) in plasma. Placental expression of the CSF-1 gene increased (p < 0.05) throughout gestation with the major increase occurring between Days 20 and 30, after which time high levels of mRNA were maintained to term. The changes in placental CSF-1 mRNA were temporally associated with periods of rapid placental and fetal growth. High levels of CSF-1 mRNA were also detected in skeletal muscle, kidney, and intestine of fetuses. Immunoreactive CSF-1 was detected in all of the tissues examined. Partial cloning of the porcine CSF-1 gene indicated greater than 98% identity with the human CSF-1 gene. CSF-1 gene expression in endometrium was not affected by exogenous E or progesterone treatment in ovariectomized gilts. These results suggest that CSF-1 may influence placental and fetal growth, and its differential expression in fetal tissues indicates that CSF-1 may also affect embryonic differentiation and growth of those tissues.