Chicken myosin IB mRNA is highly expressed in lymphoid tissues.

Little is known about the functions of members of the myosin I family in vertebrates. Chicken myosin IB is a member of the amoeba-type subclass of myosin I molecules and tissue localisation studies may provide possible clues to the functions of these myosin I molecules. The expression of the mRNA of this unconventional myosin IB was analysed by in situ hybridization and compared with that of the well characterised brush border myosin I on frozen sections of tissues from the adult domestic chicken. High levels of myosin IB mRNA were found in the intestine and spleen, but were not found in other tissues examined such as brain, heart, lung, liver and kidney. In the intestine, myosin IB mRNA was much more abundant in the lamina propria than in the enterocytes, whereas brush border myosin I mRNA was restricted to the enterocytes. In the spleen, myosin IB mRNA expression was abundant in regions of white pulp, namely germinal centres, periellipsoid lymphocyte sheaths and periarteriolar lymphocyte sheaths. Lymphocytes are the major cell type in both the lamina propria and the white pulp of the spleen, which suggests that chicken myosin IB is highly expressed in lymphocytes. Lymphocyte recirculation depends on their migration through the endothelial layer and it is possible that myosin IB may have a role to play in this type of cell motility.