Localization of alpha 4m integrin at sites of mesenchyme condensation during embryonic mouse development.

The expression and distribution of the murine alpha 4 (alpha 4m) integrin subunit and of one of its ligands, VCAM-1, were examined in the developing mouse embryo at different development stages. Transcription of the mRNA was investigated by in situ hybridization using single-stranded sense and anti-sense cDNA probes and by Northern blotting. In parallel sections integrin was identified by immunohistochemistry using the alpha 4m-specific antibody R1/2. In general both methods gave similar distributions. The results demonstrate that alpha 4m and vascular cell adhesion molecule-1 (VCAM-1) are expressed in mouse embryonic liver (E11-E15) and are developmentally down-regulated, consistent with the haematopoietic properties of embryonic liver. Developmental-stage-dependent expression of alpha 4m was also observed in lymphoid organs, such as spleen and thymus, and in some non-lymphoid organs or tissues, such as skeletal and tongue muscles, smooth muscles of the blood vessels, the outflow tract of the embryonic heart, the papilla of the tooth, the glomeruli of the kidney and the stroma of the gonads. In the latter tissues, the expression of alpha 4m correlated with the transient condensation of particular mesenchymal structures. We also confirm that VCAM-1 and alpha 4 beta 1 are co-distributed only in some tissues, suggesting that during mouse development, VLA-4 interacts mainly with another ligand, probably fibronectin.