EXPRESSION AND LOCALIZATION OF ANNEXIN-V AND ANNEXIN-VI DURING LIMB BUD FORMATION IN THE RAT FETUS

We have investigated the expression and the localization of annexin V and annexin VI during the development of rat fetal limb buds by immuno blot and immunocytochemical analysis. Neither annexin V nor annexin VI was detectable in undifferentiated mesenchymal cells in limb buds of the day-13-day-16 rat fetus. Skeletal muscles, whose progenitor cells migrate from the somites and appeared in the limb buds at day 14, dram atically expressed annexin VI on the cell surface face after different iation from mononucleated myogenic cells into multinucleated myotubes. At day 16 both annexin V and annexin VI were found to be expressed in differentiated chondrocytes as well as in the perichondrium, a precur sor of chondrocytes, whereas the compact layer of mesenchymal cells su rrounding a chondrification center (precartilage) did not show any imm unoreactivity for either of these proteins. The results suggest a clos e relationship between the expression of these annexins and cell diffe rentiation of chondrocytes and skeletal muscles during limb but develo pment.