FUNCTION: [Summary is not available for the mouse gene. This summary is for the human ortholog.] The protein encoded by this gene belongs to the CDM protein family. It is specifically expressed in hematopoietic cells and is predominantly expressed in peripheral blood leukocytes. The protein is involved in remodeling of the actin cytoskeleton required for lymphocyte migration in response to chemokine signaling. It activates members of the Rho family of GTPases, for example RAC1 and RAC2, by acting as a guanine nucleotide exchange factor (GEF) to exchange bound GDP for free GTP. [provided by RefSeq, Oct 2016] PHENOTYPE: Homozygous mutants are defective in the migration of T and B lympohcytes in response to chemokines, and thus display immune defects such as lymphocytopenia, atrophy of lymphoid follicles and loss of marginal-zone B cells. [provided by MGI curators]
Figure 1.Pier mice exhibit decreased CD4 to CD8 T cell ratios. Flow cytometric analysis of peripheral blood was utilized to determine T cell frequency. Raw data are shown. Abbreviations: WT, wild-type; REF, homozygous reference mice; HET, heterozygous variant mice; VAR, homozygous variant mice. Mean (μ) and standard deviation (σ) are indicated.
Figure 2.Pier mice exhibit increased frequencies of peripheral CD8+ T cells in CD3+ T cells. Flow cytometric analysis of peripheral blood was utilized to determine T cell frequency. Raw data are shown. Abbreviations: WT, wild-type; REF, homozygous reference mice; HET, heterozygous variant mice; VAR, homozygous variant mice. Mean (μ) and standard deviation (σ) are indicated.
Figure 3.Pier mice exhibit reduced frequencies of peripheral CD4+ T cells in CD3+ T cells. Flow cytometric analysis of peripheral blood was utilized to determine T cell frequency. Raw data are shown. Abbreviations: WT, wild-type; REF, homozygous reference mice; HET, heterozygous variant mice; VAR, homozygous variant mice. Mean (μ) and standard deviation (σ) are indicated.
The pier phenotype was identified among G3 mice of the pedigree R2885, some of which showed reduced CD4 to CD8 T cell ratios (Figure 1) due to increased frequencies of CD8+ T cells in CD3+ T cells (Figure 1) with concomitant reduced frequencies of CD4+ T cells in CD3+ T cells (Figure 3) in the peripheral blood.
Nature of Mutation
Figure 3.Linkage mapping of the reduced CD8+ T cell frequency using a recessive model of inheritance. Manhattan plot shows -log10 P values (Y-axis) plotted against the chromosome positions of 23 mutations (X-axis) identified in the G1 male of pedigree R2885. Raw phenotype data are shown for single locus linkage analysis without consideration of G2 dam identity. Horizontal pink and red lines represent thresholds of P = 0.05, and the threshold for P = 0.05 after applying Bonferroni correction, respectively.
Whole exome HiSeq sequencing of the G1 grandsire identified 23 mutations. All of the above anomalies were linked by continuous variable mapping to a mutation in Dock2: a T to A transversion at base pair 34,689,766 (v38) on chromosome 11, or base pair 94,144 in the GenBank genomic region NC_000077 for Dock2. The strongest association was found with a recessive model of inheritance to the normalized CD8+ T cell in CD3+ T cell frequency, wherein three homozygous variants departed phenotypically from 11 homozygous reference mice and 18 heterozygous mice with a P value of 2.049 x 10-6 (Figure 3).
The mutation corresponds to residue 2,058 in the mRNA sequence NM_178666 within exon 20 of 52 total exons.
The mutated nucleotide is indicated in red. The mutation results in an isoleucine to asparagine substitution at position 659 (I659N) in the DOCK2 protein, and is strongly predicted by Polyphen-2 to be damaging (score = 1.000).
Figure 4. Domain structure of mouse DOCK2. DOCK2 contains an N-terminal SH3 domain. SH3-containing DOCK proteins have been shown to interact physically with the scaffolding proteins engulfment and cell motility protein 1 (ELMO1) and ELMO2, significantly promoting Rac activation. The DHR-1 domain shares weak homology to the C2 domain. The large DHR-2 domain interacts with the nucleotide-free form of Rac. The pier mutation is indicated in red. This image is interactive. Other mutations found in DOCK2 are noted in red. Click on each mutation for more specific information.
DOCK2 belongs to the DOCK180 superfamily of guanine nucleotide exchange factors (GEFs) that have been shown to activate members of the Rho family of small GTPases [Figure 4; (1-4)]. Members of the DOCK A and B groups contain an N-terminal SH3 domain. Two domains are shared amongst all DOCK proteins, the catalytic DHR-2 (DOCK homology region 2) or CZH-2 (CDM-zizimin homology 2) domain (amino acids 1114-1620 in DOCK2) and the DHR-1 or CZH-1 domain (amino acids 420-662 in DOCK2) (2;4). Several DOCK proteins, including DOCK2, appear to be localized to the plasma membrane via interaction of the DHR-1 domain with phosphatidylinositol (3,5)-biphosphate [PtdIns(3,5)P2] and phosphatidylinositol (3,4,5) P3 (PIP3) signaling lipids (5;6). The DHR-2 domains of several DOCK family members interact with the nucleotide-free form of Rac and/or Cdc42 (2;4). DOCK2 has an N-terminal SH3 domain (amino acids 8-69).
The pier mutation results in an isoleucine to asparagine substitution at position 659 (I659N); Iso659 is within an undefined region between the DHR-1 and DHR-2 domains.
See the record frazz for more information on Dock2.
Rho GTPases are known regulators of the actin cytoskeleton and affect multiple cellular activities including cell morphology, polarity, migration, proliferation and apoptosis, phagocytosis, cytokinesis, adhesion, vesicular transport, transcription and neurite extension and retraction. Regulation of Rho GTPase activity involves the GEFs that promote the exchange of GDP for GTP, the GTPase-activating proteins (GAPs) that enhance the GTPase activity of Rho proteins, and the Rho guanine nucleotide-dissociation inhibitors (RhoGDIs) that sequester Rho GTPases in a GDP-bound state. DOCK2 functions in the polarization and migration of immune cell subsets. DOCK2 functions downstream of chemokine receptors to regulate Rac activation and migration of B and T lymphocytes, neutrophils, plasmacytoid dendritic cells (pDCs), and hematopoietic stem cells, but not monocytes or other myeloid cell types (8-10). The immune cells affected by DOCK2 deficiency display aberrant homing, activation, adhesion, polarization and migration. DOCK2-deficient lymphocytes fail to respond normally to the chemokines CCL21, CCL19, CXCL13, and CXCL12, resulting in impaired homing to secondary lymphoid organs and aberrant morphology of these tissues (8). Dock2 -/ -mice display a number of immunological phenotypes including lack of marginal zone B cells, reduced numbers of mature CD4+ T cells and the major subset of natural killer T (NKT) cells expressing the semi-invariant Vα14 T cell receptor (TCR), and aberrant TCR signaling (8;11;12). The phenotype of the pier mice indicates loss of DOCK2-assocated function.
pier(F):5'- CTCAAGTGAACTGGAAACACCG -3'
pier(R):5'- ATCATTCCAAGTCCTGTAGCTG -3'
pier_seq(F):5'- GAAACAGCTACTCAGTCTGCTTG -3'
pier_seq(R):5'- AAGTCCTGTAGCTGATTCGTGAGAC -3'