Animals Antigens Surface/genetics/metabolism Embryo Mammalian/cytology/embryology/metabolism Epithelial Cells/*metabolism Female Gene Expression Regulation Developmental Immunohistochemistry In Situ Hybridization Male Membrane Glycoproteins/genetics/metabolism Mice Inbred C57BL Knockout Nuclear Proteins/*genetics/metabolism RANK Ligand/genetics/metabolism Receptor Activator of Nuclear Factor-kappa B/genetics/metabolism Reverse Transcriptase Polymerase Chain Reaction Signal Transduction Thymus Gland/embryology/growth & development/*metabolism Time Factors Transcription Factors/genetics/metabolism