New gene, nel, encoding a Mr 93 K protein with EGF‐like repeats is strongly expressed in neural tissues of early stage chick embryos

A new gene, nel, was isolated from a 9-day-old chick embryonic cDNA library. The gene encodes a protein of 835 amino acids (93,407 M(r)) consisting of two hydrophobic domains presumed to be the signal and transmembrane sequences, a histidine rich domain, two repeats of a cysteine rich structure similar to the C-terminal domain of von Willebrand factor, five EGF-like repeats, and again two repeats of the cysteine rich sequence similar to the C-terminal domain of von Willebrand factor in the presumed cytoplasmic domain. The expression of the nel gene was studied by Northern blot and in situ hybridization analyses of chick embryos. The mRNA of the gene was found in all tissues of 10- and 17-day-old embryos by Northern blot hybridization. Among the tissues examined, the level in the brain was highest and increased with age. After hatching, gene expression was retained in the brain at about the same level found in old embryos, increased in the retina, and disappeared from the other tissues. In situ hybridization with a nel gene probe revealed that the gene was strongly expressed in neural tissues such as brain, spinal cord, and dorsal root ganglia of early embryos. Gene expression was observed in the mantle layer of the neurepithelium of the brain and of the spinal cord. Gene expression in early embryos was not restricted to the neural tissues, but was also detected in the cells around cartilage, myocardium, lung mesenchymal cells, and in the liver, etc. One band of about 4.5 Kb mRNA was detected in all tissues and stages by Northern blot hybridization analysis. The possible function of the gene is discussed.