PAXILLIN ISOFORMS IN MOUSE - LACK OF THE GAMMA-ISOFORM AND DEVELOPMENTALLY SPECIFIC BETA-ISOFORM EXPRESSION

Paxillin, a focal adhesion protein, exists as multiple isoforms in hum ans (alpha, beta, and gamma), To understand more about the physiologic al role of each isoform, we have employed the mouse system. We found t hat although the alpha and beta isoforms are present in the mouse, the gamma isoform is not. The alpha isoform protein was detected clearly in most adult tissues, whereas the beta isoform protein was almost und etectable except in spleen, testis, thymus, and lung. On the other han d, mRNAs of both isoforms were detectable in all tissues we examined. High levels of the beta isoform protein was detected in peritoneal exu date macrophage cells in adult mouse as well as in cultured fibroblast s, together with the alpha isoform, The alpha isoform was expressed at a constant level throughout the embryonic stages we examined, whereas the beta isoform protein was detected at the mid-stages of developmen t and increased to levels almost equal to those of the a isoform durin g the late stages of embryogenesis, Therefore, unlike the alpha isofor m, expression of the beta isoform protein is restricted in adult tissu es. Moreover, we showed that alpha and beta isoforms were colocalized within the same focal adhesion plaques, and cytoplasmic pools of both isoforms exist in the perinuclear area, colocalized with the Gels appa ratus.