Genes for two calcium-dependent cell adhesion molecules have similar structures and are arranged in tandem in the chicken genome.

Abstract

Genomic sequences immediately upstream of the translational start site for the chicken liver cell adhesion molecule (L-CAM) gene contain a second closely related gene, which, because of its location, we have designated the K-CAM gene. Less than 700 base pairs separate the presumed poly(A) site in the K-CAM gene from the translation initiation site for L-CAM. The sizes of exons 4-15 of the K-CAM gene are almost identical to those in the L-CAM gene and the exon/intron junctions occur at exactly equivalent positions in both genes. Exon 16, which includes the 3' untranslated region, is much shorter in the K-CAM gene and intron sizes and sequences are not generally conserved between the two genes. Probes from the K-CAM gene hybridized to a 3-kilobase mRNA that was present at high levels in embryonic skin, at lower levels in kidney, heart, and gizzard, and at still lower levels in brain and liver, as determined by Northern blotting. The sequence of the predicted gene product was nearly identical to that of the chicken B-cadherin cDNA, although the distribution of the K-CAM gene transcript differed from that reported for the cadherin. The proximity and identical overall structure of the K-CAM and L-CAM genes strongly suggest that they arose by gene duplication and raise the possibility that genes for other calcium-dependent CAMs may be located in clusters. Moreover, the tandem arrangement of the genes may have important implications for the regulation of their expression.

Large exons encoding multiple ectodomains are a characteristic feature of protocadherin genes

“…1 A) and all of the other genes characterized thus far in this cluster are interrupted by two introns. This intron͞exon organization is typical of classic cadherin genes (7)(8)(9)(10)(11). By contrast, the six ectodomains of every member of the human protocadherin ␣, ␤, and ␥ proteins are encoded in a single, unusually large exon (Fig.…”

“…Studies of the genomic organization of a number of classic cadherin genes revealed that the DNA sequences encoding individual ectodomains are interrupted by two introns (7)(8)(9)(10)(11)). An example of this is provided by human Ksp-cadherin (CDH16) gene (Fig.…”

“…The genomic organization of classic cadherins, including E-cadherin (7,8), N-cadherin (9), P-cadherin (10), and VEcadherin (11), is well characterized. In most cases, the coding region of each ectodomain is interrupted by two introns, and the positions of the introns are conserved through vertebrate evolution.…”

Genomic structure and chromosomal mapping of the mouse N-cadherin gene.

“…To understand the molecular basis of differential expression of cadherins as well as the evolution of the cadherin family, it is essential to reveal the genomic structure and chromosomal localization of each cadherin gene. Recently, the organizations of the chicken L-CAM (15) and K-CAM and the mouse P-cadherin genes were determined and compared (8,16), and the results of this study demonstrated that the exon and intron patterns are highly conserved between these three genes, although their size is very distinct. Regarding chromosomal localization, the human E-cadherin gene has been mapped to chromosome 16 (17) and the human N-cadherin gene has been mapped to chromosome 18 (18).…”

“…More than 15 members of this family have been identified; these include E-cadherin (uvomorulin) (2, 3), P-cadherin (4), N-cadherin (5,6), liver cell adhesion molecule (L-CAM) (7), and K-CAM (8). These members share a similar primary structure that is divided into the extracellular, transmembrane, and cytoplasmic domains.…”