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S. Landreville, M. Laurin, D. Verreault, C. Salesse; Expression of N-myristoyltransferases in Human Retina . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4565.
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Purpose: N-terminal myristoyltransferase (NMT) is suspected as the enzyme responsible for the heterogeneous N-acylation of numerous retinal proteins. NMT types were previously identified in bovine retinal and human liver tissues. This study was undertaken to determine whether tissue-specific NMTs are expressed in human retina. Methods: The mRNAs of human retinal NMTs (hrNMTs) were extracted and amplified by RT-PCR from human retinal tissues. The cDNAs of hrNMTs were then cloned and sequenced for putative open reading frames. The expression of different hrNMTs translated in vivo was detected by Western immunoblotting on retinal protein extracts. The localization of hrNMTs was determined by immunohistochemistry on flatmounted retinal sections. Results: Open reading frames of 1488 and 1494 bp were found, respectively, for hrNMT-1 and hrNMT-2 cDNA sequences. cDNA of a spliced isoform of hrNMT-1 was also identified. hrNMT-2 with an apparent molecular mass of 65 kDa as well as three different isoforms of hrNMT-1 with apparent molecular masses of, respectively, 49, 63 and 68 kDa were found in retinal extracts by Western immunoblotting. The intensity of hrNMT-1L was much more pronounced than that of hrNMT-1M and hrNMT-1S. Immunohistochemical analysis of tissue sections showed that hrNMT-1 and hrNMT-2 proteins are expressed in all retinal cells, except in the photoreceptor outer segments. However, the expression of hrNMT-2 was less pronounced. Conclusion: Two types of NMTs, which are similar to those derived from other mammalian tissues investigated so far, are expressed in human retina. These results together with the previous identification of the same NMTs in other bovine and human tissues suggest that no retina-specific NMTs are expressed. However, the different levels of expression of hrNMT-1 isoforms could be important for the heterogeneous retinal N-acylation.
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