Alternative titles; symbols
HGNC Approved Gene Symbol: ROBO2
Cytogenetic location: 3p12.3 Genomic coordinates (GRCh38): 3:75,906,675-77,649,964 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 3p12.3 | Vesicoureteral reflux 2 | 610878 | Autosomal dominant | 3 |
Members of the ROBO family, such as ROBO2, function as axon guidance receptors by binding secreted SLIT ligands (see SLIT1; 603742) (Fricke et al., 2001).
Kidd et al. (1998) cloned the Drosophila roundabout (robo) gene, which encodes an axon guidance receptor that defines a novel subfamily of immunoglobulin superfamily proteins that is highly conserved from fruit flies to mammals. They used protein sequence homologies to clone the partial sequence of ROBO2 and the full sequence of ROBO1 (602430), human homologs of the Drosophila robo gene.
By sequencing clones obtained from a size-fractionated fetal brain cDNA library, Nagase et al. (2000) cloned ROBO2, which they designated KIAA1568. The deduced 1,380-amino acid protein shares 56% identity with ROBO1. RT-PCR ELISA detected highest expression of ROBO2 in adult and fetal brain, adult ovary, and in most individual brain regions examined. Intermediate expression was detected in fetal liver and in adult lung, kidney, spleen, testis, and spinal cord. Little to no expression was detected in adult pancreas, heart, liver, and skeletal muscle.
By RT-PCR of fetal brain RNA, followed by 5-prime RACE, Yue et al. (2006) cloned 2 splice variants of ROBO2, which they called ROBO2a and ROBO2b. ROBO2b and ROBO2a have start codons in exons 1 and 2, respectively, and encode proteins with different N termini and signal peptides. The mature ROBO2b protein is 4 residues shorter than the mature ROBO2a protein. RT-PCR detected ROBO2b expression in all tissues examined except skeletal muscle. ROBO2a showed a more restricted expression pattern, with highest expression in fetal brain and significantly lower levels in adult brain, kidney, spleen, testis, and spinal cord. Both isoforms were detected in human fetal brain at all developmental stages examined. Yue et al. (2006) also identified mouse Robo2a and Robo2b and found that both use 4 alternative 3-prime ends, resulting in 8 different mouse Robo2 transcripts and protein isoforms. RT-PCR detected mouse Robo2a in adult brain and whole embryo only, whereas Robo2b was expressed in these and other adult tissues.
Using in situ hybridization analysis, Bagri et al. (2002) detected expression of Robo1 and Robo2 in the developing cortex and thalamus of mouse embryos. They detected a complementary pattern of expression of Robo and Slit genes in the developing mouse forebrain and concluded that these molecules may play a role in the guidance of corticofugal and thalamocortical projections.
Yue et al. (2006) determined that the ROBO2 gene contains at least 27 exons. It has 2 alternative first exons and 2 alternative promoters.
By genomic sequence analysis, Yue et al. (2006) mapped the ROBO2 gene to chromosome 3p12.3. They found that the 3-prime end of mouse Robo2 lies in a region of chromosome 16C3.1 that shares homology of synteny with human chromosome 3p12.3. However, the most 5-prime exon of mouse Robo2 lies in a DNA segment of more than 150 kb that shows a break in synteny between the mouse and human genomes.
Kidd et al. (1998) identified the robo gene in Drosophila in a large-scale mutant screen for genes that control the decision by axons to cross the central nervous system midline. In robo mutants, too many axons cross and recross the midline. For those axons in Drosophila that never cross the midline, robo is expressed on their growth cones from the outset; for the majority of axons that do cross the midline, robo is expressed at high levels on their growth cones only after they cross the midline. Transgenic rescue experiments in Drosophila revealed that robo can function in a cell-autonomous fashion. The authors concluded that robo functions as the gatekeeper controlling midline crossing.
Congenital anomalies of the kidney and urinary tract (CAKUT) include vesicoureteral reflux (VUR; see 193000). Lu et al. (2007) investigated a man with a de novo translocation, 46,X,t(Y;3)(p11;p12), who exhibited multiple congenital abnormalities, including severe bilateral VUR with ureterovesical junction defects. This translocation disrupted the ROBO2 gene, which encodes a transmembrane receptor for SLIT ligand (see SLIT2, 603746), and produced dominant-negative ROBO2 proteins that abrogated SLIT/ROBO signaling in vitro. In an investigation to test whether mutations in ROBO2 are associated with CAKUT and VUR in the general population, Lu et al. (2007) identified 2 novel ROBO2 intracellular missense variants that segregated with CAKUT and VUR in 2 unrelated families (see VUR2, 610878). These results, as well as the findings in mutant mice with reduced Robo2 gene dosage showing striking CAKUT-VUR phenotypes, implicated the SLIT-ROBO signaling pathway in the pathogenesis of a subset of human VUR. Lu et al. (2007) observed that both the ile945 to thr (602431.0001) and ala1236 to thr (602431.0002) mutations involve residues evolutionarily conserved in all mammals that are only slightly divergent in birds and fish, organisms that lack a urinary bladder and ureterovesical junction.
By screening the ROBO2 gene in a cohort of 95 unrelated Italian patients with primary VUR or VUR/CAKUT, Bertoli-Avella et al. (2008) identified 4 likely pathogenic missense mutations (G328S, N515I, D766G, R797Q) that segregated with the disorder in the families. Some asymptomatic family members were also found to carry the mutation, consistent with incomplete penetrance. The mutations were not found in 190 Italian control individuals. The authors noted that functional studies of the variants and replication in other cohorts were warranted.
Dobson et al. (2013) screened the ROBO2 gene in a cohort of 227 Irish patients with VUR. They did not find any of the 6 previously identified ROBO2 mutations, but identified 2 other novel mutations (P522T and V799I) that segregated with the disorder in the families. The P522T variant was not found in 592 control individuals and the V799I mutation was found in 1 control. Dobson et al. (2013) noted that of the 35 ROBO2 nonsynonymous variants that had been identified, the predicted pathogenicity of those found exclusively in VUR patients did not differ from that predicted for those variants also found in controls. The authors concluded that the pathogenicity of the variants is uncertain.
Grieshammer et al. (2004) found that mice lacking either Robo2 or its ligand, Slit2 (603746), developed supernumerary uretic buds that remained inappropriately connected to the nephric duct. In addition, Gdnf (600837) expression was inappropriately maintained in anterior nephrogenic mesenchyme in these mutants. Grieshammer et al. (2004) concluded that SLIT2/ROBO2 signaling restricts the extent of the GDNF expression domain, thereby precisely positioning the site of kidney induction.
Mutations in the zebrafish 'astray' gene severely disrupt retinal axon guidance, causing anterior/posterior pathfinding defects, excessive midline crossing, and defasciculation of the retinal projection. Eye transplantation experiments showed that astray function is required in the eye. Fricke et al. (2001) identified astray as zebrafish robo2. Retinal ganglion cells express robo2 as they extend axons. Thus, robo2 is required for multiple axon guidance decisions during establishment of the vertebral visual projection.
Using a zebrafish model, Xiao et al. (2011) showed that the type IV collagen Col4a5 (303630) on the surface of the tectum basement membrane bound Slit1 and guided retinal ganglion cell axons expressing Robo2.
In a British family with vesicoureteral reflux (VUR2; 610878), Lu et al. (2007) found heterozygosity for a T-to-C transition at position 3477 in coding exon 19 of the ROBO2 gene. This change was predicted to cause a nonconservative missense substitution, ile945 to thr (I945T), in the ROBO2 intracellular domain.
In a Dutch family with vesicoureteral reflux (VUR2; 610878), Lu et al. (2007) found heterozygosity for a G-to-A transition at nucleotide 4349 in coding exon 23 of the ROBO2 gene that was predicted to cause a nonconservative missense amino acid substitution, ala1236 to thr (A1236T), in the ROBO2 intracellular domain. The mutation was found in 5 affected members of the family; a sixth family member, an uncle of the proband, also had this alteration but did not exhibit an ultrasonographically detectable renal phenotype. Lu et al. (2007) considered this an example of nonpenetrance.
Bagri, A., Marin, O., Plump, A. S., Mak, J., Pleasure, S. J., Rubenstein, J. L. R., Tessier-Lavigne, M. Slit proteins prevent midline crossing and determine the dorsoventral position of major axonal pathways in the mammalian forebrain. Neuron 33: 233-248, 2002. [PubMed: 11804571] [Full Text: https://doi.org/10.1016/s0896-6273(02)00561-5]
Bertoli-Avella, A. M., Conte, M. L., Punzo, F., de Graaf, B. M., Lama, G., La Manna, A., Polito, C., Grassia, C., Nobili, B., Rambaldi, P. F., Oostra, B. A., Perrotta, S. ROBO2 gene variants are associated with familial vesicoureteral reflux. J. Am. Soc. Nephrol. 19: 825-831, 2008. [PubMed: 18235093] [Full Text: https://doi.org/10.1681/ASN.2007060692]
Dobson, M. G., Darlow, J. M., Hunziker, M., Green, A. J., Barton, D. E., Puri, P. Heterozygous non-synonymous ROBO2 variants are unlikely to be sufficient to cause familial vesicoureteric reflux. Kidney Int. 84: 327-337, 2013. [PubMed: 23536131] [Full Text: https://doi.org/10.1038/ki.2013.100]
Fricke, C., Lee, J.-S., Geiger-Rudolph, S., Bonhoeffer, F., Chien, C.-B. astray, a zebrafish roundabout homolog required for retinal axon guidance. Science 292: 507-510, 2001. [PubMed: 11313496] [Full Text: https://doi.org/10.1126/science.1059496]
Grieshammer, U., Ma, L., Plump, A. S., Wang, F., Tessier-Lavigne, M., Martin, G. R. SLIT2-mediated ROBO2 signaling restricts kidney induction to a single site. Dev. Cell 6: 709-717, 2004. [PubMed: 15130495] [Full Text: https://doi.org/10.1016/s1534-5807(04)00108-x]
Kidd, T., Brose, K., Mitchell, K. J., Fetter, R. D., Tessier-Lavigne, M., Goodman, C. S., Tear, G. Roundabout controls axon crossing of the CNS midline and defines a novel subfamily of evolutionarily conserved guidance receptors. Cell 92: 205-215, 1998. [PubMed: 9458045] [Full Text: https://doi.org/10.1016/s0092-8674(00)80915-0]
Lu, W., van Eerde, A. M., Fan, X., Quintero-Rivera, F., Kulkarni, S., Ferguson, H., Kim, H.-G., Fan, Y., Xi, Q., Li, Q., Sanlaville, D., Andrews, W., and 15 others. Disruption of ROBO2 is associated with urinary tract anomalies and confers risk of vesicoureteral reflux. Am. J. Hum. Genet. 80: 616-632, 2007. [PubMed: 17357069] [Full Text: https://doi.org/10.1086/512735]
Nagase, T., Kikuno, R., Nakayama, M., Hirosawa, M., Ohara, O. Prediction of the coding sequences of unidentified human genes. XVIII. The complete sequences of 100 new cDNA clones from brain which code for large proteins in vitro. DNA Res. 7: 273-281, 2000. [PubMed: 10997877] [Full Text: https://doi.org/10.1093/dnares/7.4.271]
Xiao, T., Staub, W., Robles, E., Gosse, N. J., Cole, G. J., Baier, H. Assembly of lamina-specific neuronal connections by slit bound to type IV collagen. Cell 146: 164-176, 2011. [PubMed: 21729787] [Full Text: https://doi.org/10.1016/j.cell.2011.06.016]
Yue, Y., Grossmann, B., Galetzka, D., Zechner, U., Haaf, T. Isolation and differential expression of two isoforms of the ROBO2/Robo2 axon guidance receptor gene in humans and mice. Genomics 88: 772-778, 2006. [PubMed: 16829019] [Full Text: https://doi.org/10.1016/j.ygeno.2006.05.011]