Mutant mice show T cell defects. Null mutants lack alpha-beta T cells in the thymus and have fewer T cells in dendritic and intestinal epithelium. Spontaneous and knock-in missense mutations affect T cell receptor signaling, one of the former resulting in severe chronic arthritis.
The mrtless (mrt) phenotype was identified in a flow cytometry screen of blood from N-ethyl-N-nitrosourea (ENU)-mutagenized mice for mutations affecting the circulating proportions of memory and naïve T cells (1). Homozygous mrtless mice display an almost complete arrest of T cell development at the CD4+CD8+ double positive (DP) stage resulting in very few peripheral T cells. Cluster of differentiation 5 (CD5) and CD69 are upregulated on T cells in response to T cell activation. A comparison of CD5 and CD69 expression in Zap70mrt/mrt and homozygous null Zap70−/− animals established that Zap70mrt/mrt thymocytes have greater responsiveness to TCR stimulation than thymocytes with no ZAP-70 (Figure 1).
Please see the record for murdockfor more information about the Zap70mrt allele.
Nature of Mutation
The mrtless mutation was mapped to Chromosome 1, and corresponds to a T to C transition at position 1601 of the Zap70 transcript, in exon 11 of 13 total exons.
The mutated nucleotide is indicated in red lettering and causes a tryptophan to arginine change at amino acid 504 of the encoded protein.
Figure 2. Structure of ZAP-70. Mouse Zap-70 is a 618 amino acid protein tyrosine kinasen (PTK) that consists of two N-terminal Src-homology 2 (SH2) domains and a C-terminal kinase domain. The SH2 domains are connected by a linker known as interdomain A (IDA), while the region between the second SH2 and catalytic domains is known as interdomain B (IDB). The aspartic acid (D) of the residue 459 is the proton acceptor during the catalytic cycle. Several tyrosine (Y) residues located within interdomain B are phosphorylated following TCR stimulation (291, 314, and 318). Phosphorylation of Tyr 492 is required for ZAP-70 activation, while Tyr 491 phosphorylation negatively regulates ZAP-70 function. The mrtless mutation causes a tryptophan to arginine change at amino acid 504. The 3D structure is human ZAP70. UCSF Chimera structure based on PDB 2OZO. This image is interactive. Click on the image to view other mutations found in ZAP-70 (red). Click on the mutations for more specific information. Click on the 3D structure to view it rotate.
The mrtless mutation results in a tryptophan to arginine substitution of a conserved residue in the activation loop within the catalytic site of the kinase domain at amino acid 504 (Figure 2). The aberrant protein is expressed at 25% of wild-type levels (1).
Please see the record for murdock for more information about Zap70.
Primers cannot be located by automatic search.
Genotyping protocols are from the Australian PhenomeBank.