Differential expression of murine exon 1 in trophoblast cells.

(A) Exon 1 is expressed only in mouse placenta. This panel shows 20 μg total RNA from L cells, a fibroblast cell line which does not express the fms gene, c-fms–positive macrophage cell line BAC1.2F5 cells, and e10 and e14 mouse placental RNA, probed with either an exon 2 or an exon 1 probe. (B) Exon 1 is expressed in trophoblastic cells. BAC1.2F5, mouse embryo fibroblasts (MEFs), trophoblastic stem cells (TSs), or e14 placentae were probed with exon 1 or exon 2 probes. In each panel the ethidium-bromide staining of 18S rRNA was used to monitor the loading of the RNAs.