Molecular cloning of Ly-1, a membrane glycoprotein of mouse T lymphocytes and a subset of B cells: molecular homology to its human counterpart Leu-1/T1 (CD5).

Abstract

We report the isolation of cDNA clones of the mouse lymphocyte differentiation antigen Ly-l. One of these cDNA clones was confirmed to be full-length by DNA sequencing and by expression of Ly-1 by L cells transfected with this clone. Analysis of the predicted amino acid sequence indicated that the Ly-1 polypeptide is synthesized with a 23 amino acid leader and that the mature protein consists of an aminoterminal region of 347 amino acids, a transmembrane sequence of 30 residues, and a carboxyl-terminal region of 94 amino acids. The amino-terminal region appears to be divided into two subregions by a threonine-and proline-rich sequence of 23 amino acids that is highly conserved between Ly-1 and its human homologue Leu-1 (CD5) in position and amino acid composition. The first amino-terminal subregion of 111 amino acids is predicted to be arranged in a P-pleated sheet structure of six strands. The entire amino-terminal region is rich in cysteine, with all of its 22 cysteine residues conserved between Ly-1 and Leu-1. The carboxyl-terminal region has no cysteines. Ly-1 and Leu-1 are 63% identical, with a gradient of identical residues from 43% for the first amino-terminal subregion to 58% for the second amino-terminal subregion and 90% for the carboxyl-terminal region. The predicted secondary structure of the first amino-terminal subregion and identities of certain conserved residues among most members of the immunoglobulin gene superfamily suggest that Ly-1 and Leu-1 are distant members of this family.Ly-1 (formerly Lyt-1), a lymphocyte differentiation antigen with a molecular weight of 67,000, is expressed on nearly all murine thymocytes (1, 2). Cytotoxic-depletion studies originally suggested that Ly-1 was selectively expressed on helper T cells (3). Sensitive analyses, such as those using the fluorescence-activated cell sorter (FACS), have shown that Ly-1 is a pan-T marker present at a higher level on helper T cells than on suppressor or cytotoxic T cells (1, 2). Levels of Ly-1 within the range of Ly-1 levels on cytotoxic/suppressor T cells have been found on some B-cell tumors (4) and on a distinct subpopulation and lineage of B cells in normal animals (5, 6).Little is known about the role of Ly-1 in lymphocyte function and/or differentiation. Antibodies against Ly-1 molecules can augment alloantigen-or mitogen-induced lymphocyte proliferation, suggesting a possible role for Ly-1 in regulating T-cell proliferation (7,8). The enhancing effect of anti-Ly-1 antibodies on T-cell proliferation is associated with the increased secretion of interleukin 2 (IL-2) and the increased expression of the IL-2 receptor. Similar enhancing properties of anti-Ly-1 antibodies were observed for the human and rat Ly-1 homologs (9-11).

LYAR, a novel nucleolar protein with zinc finger DNA-binding motifs, is involved in cell growth regulation.

“…It was ruled out as encoding Ly-1 by chromosomal mapping {see below]. Comparison of LYAR to the Ly-1 sequences, subsequently elucidated by others {Huang et al 1987), showed that they encoded polypeptides with no significant similarity.…”

Structure and Chromosomal Localization of Chicken CD5

“…However, the cytoplasmic tail of CD5 is encoded in three exons. The introns in the chicken CD5 gene are localized similarly to the corresponding human and mouse introns [4,12]. However, immediately after the stop codon there is an intron in the human sequence that is not found either in our clone or in the genomic DNA of H.B2 strain chicken.…”

“…Chicken CD5 is structurally conserved, especially in its cytoplasmic domain which includes identical regions to mammalian sequence with potential functional motifs [4,5]. In chicken the CD5 is expressed at high levels on all ab T cells, whereas a low or intermediate expression is found on gd T cells depending on their tissue location [5].…”

Genetics, FACS, Immunology, and Redox: A Tale of Two Lives Intertwined

“…In addition, of key importance for gene cloning and expression studies, these complementary tools provide the ability to select cells expressing particular molecules or variants thereof. Thus, among other things, they allowed us to clone the murine CD8 and CD5 genes (63)(64)(65) and to explore the gene amplification (double-minute/minichromosome) mechanism (66) that controlled the level of expression of the CD8 gene cloned into a nonlymphoid cell line.…”