FUNCTION AND SPATIAL-DISTRIBUTION IN DEVELOPING CHICK RETINA OF THE LAMININ RECEPTOR ALPHA-6-BETA-1 AND ITS ISOFORMS

We have recently shown that the laminin-binding integrin receptor, alp ha6beta1, is prominently expressed in the developing chick retina, and its expression and activity are regulated during development on both retinal ganglion cells and other neural retinal cells. In the present study, we show that antibodies specific for the extracellular portion of the chick alpha6 subunit dramatically inhibit interactions in vitro between embryonic day 6 neural retinal cells and laminin, showing tha t alpha6beta1 functions as an important laminin receptor on developing retinal neurons. In previous work, we showed that alpha6 mRNA levels on retinal ganglion cells decrease dramatically after E6 during the pe riod that RGC axons innervate the optic tectum. In the present study, we show decreases in alpha6 mRNA are not prevented by ablation of the optic tectum, indicating that tectal contact is not the major cause of this decrease. Within the embryonic retina, the alpha6 subunit is cod istributed, in part, with laminin, suggesting that it functions as a l aminin receptor during retina development in vivo. Furthermore, two is oforms of the alpha6 protein with distinct cytoplasmic domains generat ed by differential splicing have quite different distribution patterns in the retina, suggesting that these two isoforms may have different functions during retinal development.