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We report the isolation and characterization of a Xenopus sequence, XNLRR-1, that is closely related to a gene for mouse neuronal leucine-rich repeat protein (NLRR-1). The cDNA clone is 4179 bp long and encodes a putative transmembrane glycoprotein of 718 amino acids, containing 12 leucine-rich repeats followed by one C2-type immunoglobulin-like domain and one fibronectin type-III repeat. XNLRR-1 is transcribed mainly in the developing eye area and the ventricular zone from diencephalon to hindbrain and slightly in spinal cord in Xenopus tadpoles. The similarity of the XNLRR-1 gene to other known cell adhesion molecules, together with the expression pattern, suggests that XNLRR-1 is involved in interactions at the neuronal cell surface.
The XNLRR-1 cDNA sequence predicts a glycosylated transmembrane protein. (A) cDNA sequence and deduced amino acid sequence of XNLRR-1. Poly(A) adenylation signal sequence (AATAAA) is highlighted. The putative hydrophobic signal sequence and transmembrane region are marked by underlines and dotted underlines, respectively. Potential N-linked glycosylation sites are highlighted in the square box. (B) Hydrophobicity analysis (Kyte and Doolittle, 1982) of the predicted amino acid sequence of XNLRR-1 with a window of five residues indicating the N-terminal and C-terminal hydrophobic stretches, characteristic of signal sequence and transmembrane region, respectively. The hydrophobic stretches appear as positive values. Both regions are indicated. Sig, signal sequence; TM, transmembrane.
Alignment of the LRR domains of XNLRR-1. Consensus sequences are highlighted and also shown below
Amino acid sequence comparison of XNLRR-1 with NLRR-1 and NLRR-3. XNLRR-1 shares 80% amino acid identity with NLRR-1 and 51% identity with NLRR-3. Identical amino acids are indicated by dots, and spaces (dashes) have been introduced to maximize the homology. The putative signal sequence is underlined. The LRR domains are double-underlined. The AFR and CFR are marked by a dashed line and dotted line, respectively. Square boxes indicate the conserved cysteins of Ig domains. Circles indicate tyrosine and tryptophan residues that are characteristic of FN III repeats. Transmembrane regions are wave-underlined.
Comparative analysis of AFRs, CFRs, Ig domains and FN III repeats of XNLRR-1 with other related proteins. Databases were searched with individual domains. Conserved cystein residues are underlined. Consensus sequences are shown below. (A) Alignment of AFRs. (B) Alignment of CFRs. (C) Alignment of C2-type Ig-like domains. DLAR, Drosophila receptor tyrosine kinase. (D) Alignment of FN III repeats. Conserved tryptophan and tyrosine residues are underlined. fib, fibronectin; PTP, receptor-like protein tyrosine phosphatase; tena, Tenascin.
Spatial expression pattern of XNLRR-1 by whole-mount in-situ hybridization. (A) Dorsal view of a stage 33 embryo showing staining of the ventricular zone from the diencephalon to the hindbrain. (B) Lateral view of the embryo pictured in (A), showing staining of the developing eye area and the brain. A weak signal is also detected in the spinal cord. SC, spinal cord; VZ, ventricular zone.