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The developmental expression of three mammalian lens fiber cell membrane proteins
L J Jarvis1, N M Kumar, C F Louis
1Department of Biochemistry, University of Minnesota, St. Paul 55108.
Purpose:
The expression of the lens fiber cell integral membrane proteins MP20, the alpha 3 gap junction protein (connexin 46), and MP26 (MIP) was determined both during development of the bovine fetal lens and in different animal species.
Methods:
The relative levels of the mRNA species coding for these proteins was determined by Northern blotting; this was correlated with the amounts of these proteins as determined by Western immunoblotting.
Results:
RNA extracted from fetal calf lenses at 3-4, 5-6, and 7-8 mo gestation, and from postnatal calf lenses, showed a progressive decrease of the mRNA species coding for MP20 (20-fold), alpha 3 gap junction protein (22-fold), and MP26 (12-fold) with development. This compared with a 6-fold decrease in total RNA and a 15-fold decrease in poly-A(+) RNA over the same period. In contrast to these significant changes in the levels of mRNA, there were no significant changes in the concentrations of these proteins over the same period. Whereas the mRNA coding for each of these proteins were concentrated in the lens cortical regions. MP20 and MP26 protein concentrations in cortical and nuclear regions were very similar. Both protein and mRNA coding for MP20, alpha 3 gap junction, and MP26 were detected in calf, sheep, pig, and rat lenses.
Conclusions:
These results indicate that the expression of the mRNA coding for the lens fiber cell integral membrane proteins MP20, alpha 3 gap junction, and MP26 is regulated and may be coordinated. That the decrease in mRNA concentrations is not correlated with changes in the concentrations of these lens membrane proteins indicates their unique stability.