Function and spatial distribution in developing chick retina of the laminin receptor α6β1 and its isoforms

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Abstract
We have recently shown that the laminin-binding integrin receptor, α 6 β 1, 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 α6 subunit dramatically inhibit interactions in vitro between embryonic day 6 neural retinal cells and laminin, showing that α 6 β 1 functions as an important laminin receptor on developing retinal neurons. In previous work, we showed that α6 mRNA levels on retinal ganglion cells decrease dramatically after E6 during the period that RGC axons innervate the optic tectum. In the present study, we show decreases in α6 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 α 6 subunit is codistributed, in part, with laminin, suggesting that it functions as a laminin receptor during retina development in vivo. Furthermore, two isoforms of the α 6 protein with distinct cytoplasmic domains generated by differential splicing have quite different distribution patterns in the retina, suggesting that these two isoforms may have different functions during retinal development.

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