Alternative titles; symbols
HGNC Approved Gene Symbol: ROBO3
Cytogenetic location: 11q24.2 Genomic coordinates (GRCh38): 11:124,865,432-124,881,471 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 11q24.2 | Gaze palsy, familial horizontal, with progressive scoliosis, 1 | 607313 | Autosomal recessive | 3 |
ROBO3 is a multifunctional receptor involved in axon guidance during development. It plays a critical role in allowing commissural axons to reach and cross the spinal cord midline (summary by Jaworski et al., 2015).
Yuan et al. (1999) identified a divergent member of the Robo subfamily (see 602430), Rig1, as a gene that was upregulated in mouse Rb1 (614041)-deficient embryos. The deduced 1,344-amino acid protein contains an N-terminal signal peptide, followed by an extracellular domain, a transmembrane region, and a C-terminal intracellular domain. The extracellular portion contains 5 immunoglobulin-like domains and 3 fibronectin (135600) type III-like domains, which are commonly present in growth factor receptors and proteins involved in cell adhesion and differentiation. Western blot analysis of fractionated embryonic day-11.5 mouse hindbrain and spinal cord cells detected Rig1 in the membrane fraction. Rig1 showed an apparent molecular mass of about 210 kD. Yuan et al. (1999) also identified 8 alternatively spliced transcripts of mouse Rig1. Two of the alternatively spliced exons are in-frame, while others introduce stop codons, indicating that Rig1 can encode both transmembrane and secreted proteins.
Sabatier et al. (2004) stated that mouse Rig1 shares 40% amino acid identity with other vertebrate members of the Robo family, particularly in its extracellular domain, but is missing important cytoplasmic motifs found in other Robo family members.
Jen et al. (2004) determined that, homologous to other members of the roundabout family, the predicted 1,384-amino acid sequence of ROBO3 contains a putative extracellular segment with 5 immunoglobulin-like motifs and 3 fibronectin-like motifs, a transmembrane segment, and an intracellular segment with 3 cytoplasmic signaling motifs: CC0, CC2, and CC3. The CC1 motif, which is absent in human ROBO3 and mouse Rig1 but present in other homologs, interacts with DCC (120470) to silence Netrin-1 (601614)-attractive effects (Stein and Tessier-Lavigne, 2001). Note that an expression of concern was published for the article by Stein and Tessier-Lavigne (2001).
Yuan et al. (1999) determined that mouse Rig1 contains at least 9 alternatively spliced exons.
Jen et al. (2004) found that the ROBO3 gene contains 28 exons spanning approximately 16,000 bases.
Jen et al. (2004) identified the ROBO3 gene within the disease locus for familial horizontal gaze palsy with progressive scoliosis (HGPPS1; 607313) on chromosome 11q23-q25.
Gross (2016) mapped the ROBO3 gene to chromosome 11q24.2 based on an alignment of the ROBO3 sequence (GenBank BC008623) with the genomic sequence (GRCh38).
Yuan et al. (1999) determined that full-length mouse Rig1, but not the extracellular N-terminal domain, promoted neuronal cell entrance to S phase and repressed the expression of tubulin alpha-1 (191110), a marker of neuronal differentiation.
Sabatier et al. (2004) found that Rig1 was specifically expressed by commissural axons in rodents. Unexpectedly for a Robo family member, however, Rig1 was highly expressed before midline crossing and downregulated after crossing. Loss-of-function studies in mice showed that Rig1 was required to allow commissural axons to enter the floor plate and cross to the contralateral side of the spinal cord. Based on in vitro and in vivo studies, Sabatier et al. (2004) proposed that Rig1 normally functions to inhibit the ability of precrossing commissural axons to sense floor plate repellents of the Slit family (see 603742) through Robo receptors, thus allowing the axons to cross the midline.
By in situ hybridization, Jen et al. (2004) demonstrated abundant expression of the ROBO3 gene in the basis pontis in 15- and 19-week-old fetal human brain. This observation is consistent with the hindbrain-specific expression of mouse Rig1. That patients with horizontal gaze palsy with progressive scoliosis (HGPPS1; 607313), in whom mutations in the ROBO3 gene are found, have motor and sensory axon projections that do not appear to cross the midline confirms that ROBO3 is required for hindbrain axon midline crossing.
Jaworski et al. (2015) noted that the mouse Robo3.1 isoform is expressed on commissural axons prior to midline crossing and allows midline crossing by inhibiting Slit repulsive guidance cues. In contrast, the mouse Robo3.2 isoform is expressed after midline crossing and prevents midline recrossing. Jaworski et al. (2015) found that the isolated ectodomain of mouse Robo3 fused to the IgG (see 147100) Fc fragment (Robo3-ECD-Fc) bound Nell2 (602320)-Fc. Robo3-ECD-Fc also bound GFP-tagged Nell2 expressed in HEK293T cells. A Nell2-alkaline phosphatase (see 171760) chimera bound Robo3.1 and Robo3.2. Deletion analysis revealed that the EGF-like domains of Nell2 bound the fibronectin III domains of Robo3. Explants of commissural axons of embryonic mouse dorsal spinal cord, which express Robo3.1, grew away from COS-7 cells expressing Nell2, whereas explants of postcrossing commissural axons, which express Robo3.2, did not. Robo3- and Nell2-knockout studies in mice confirmed that Nell2 provided a repulsive guidance cue to prevent commissural axons from entering the motor column.
In patients with familial horizontal gaze palsy with progressive scoliosis (HGPPS1; 607313), Jen et al. (2004) identified 10 different homozygous mutations (608630.0001-608630.0010) in the ROBO3 gene. They identified 6 missense, 1 nonsense, 1 splice site, and 2 frameshift mutations. Four of the 6 missense mutations resulted in nonconservative changes in evolutionarily conserved amino acids. Nine of the 10 mutations were located in the extracellular domains of the ROBO3 protein.
In 2 unrelated children with sporadic HGPPS, born of nonconsanguineous parents, Chan et al. (2006) identified compound heterozygosity for 2 different 2-bp deletions (608630.0011 and 608630.0012) and a missense and a nonsense mutation (608630.0013 and 608630.0014) in the ROBO3 gene, respectively.
In a consanguineous Indian family with horizontal gaze palsy with progressive scoliosis-1 (HGPPS1; 607313), Jen et al. (2004) identified homozygosity for a 1082G-A transition in exon 7 of the ROBO3 gene. This resulted in a gly361-to-glu (G361E) substitution that occurred in the fourth Ig domain of the gene. The mutation was not identified in 95 control samples from the same population.
In a consanguineous Saudi family with horizontal gaze palsy with progressive scoliosis-1 (HGPPS1; 607313), Jen et al. (2004) identified homozygosity for a frameshift mutation in exon 23 of the ROBO3 gene, insertion of a G at nucleotide 3325 (3325+1G). This mutation, not identified in 116 control samples, occurred between the CC2 and CC3 domains and was predicted to incorporate novel sequences following CC2 and result in premature termination of the ROBO3 protein. If stable, the truncated receptor should retain much of the wildtype protein except for the C terminus, where CC3 resides. Therefore, it is possible that CC3 is required for the normal function of ROBO3; alternatively, the frameshift mutation may interfere with protein folding and trafficking.
In a consanguineous Turkish family with horizontal gaze palsy with progressive scoliosis-1 (HGPPS1; 607313), Jen et al. (2004) identified homozygosity for a 2108G-C transversion in exon 14 of the ROBO3 gene. This resulted in an arg703-to-pro (R703P) substitution in a conserved residue of the Fn3 II domain. This mutation was not identified in 150 control samples.
In a consanguineous Saudi family with horizontal gaze palsy with progressive scoliosis-1 (HGPPS1; 607313), Jen et al. (2004) identified homozygosity for a 2113T-C transition in exon 14 of the ROBO3 gene. This resulted in a ser705-to-pro (S705P) substitution in the Fn3 II domain of the gene. This mutation was not identified in 116 control samples.
In a consanguineous Turkish family with horizontal gaze palsy with progressive scoliosis-1 (HGPPS1; 607313), Jen et al. (2004) identified homozygosity for a 1366G-T transversion in exon 9 of the ROBO3 gene, resulting in a gly456-to-stop (G456X) substitution between the Ig-like domains IV and V. This mutation was not identified in 95 control samples.
In a consanguineous Greek family with horizontal gaze palsy with progressive scoliosis-1 (HGPPS1; 607313), Jen et al. (2004) identified homozygosity for a 955G-A transition in exon 6 of the ROBO3 gene, resulting in a glu319-to-lys (E319K) substitution. This mutation occurred in the Ig-like domain III of the gene and was not identified in 197 control samples.
In a consanguineous Pakistani family with horizontal gaze palsy with progressive scoliosis-1 (HGPPS1; 607313), Jen et al. (2004) identified homozygosity for a frameshift mutation in exon 15 of the ROBO3 gene, insertion of a C at nucleotide 2310 (2310+1C) in the Fn3 III domain. This mutation was not identified in 106 control samples.
In a consanguineous Italian family with horizontal gaze palsy with progressive scoliosis-1 (HGPPS1; 607313), Jen et al. (2004) identified homozygosity for a 14T-C transition in exon 1 of the ROBO3 gene, resulting in a leu5-to-pro (L5P) substitution. The L5P mutation occurred within the predicted signal sequence important for posttranslational membrane targeting and insertion. Although a proline-for-leucine substitution does not alter the net charge, it may disrupt the secondary structure of the signal sequence. This mutation was not identified in 106 control samples.
In a consanguineous Greek family with horizontal gaze palsy with progressive scoliosis-1 (HGPPS1; 607313), Jen et al. (2004) identified homozygosity for a 196A-C transversion in exon 2 of the ROBO3 gene, resulting in an ile66-to-leu (I66L) substitution in the Ig-like domain I of the protein. This mutation was not identified in 175 control samples.
In a consanguineous Arab family with horizontal gaze palsy with progressive scoliosis-1 (HGPPS1; 607313), Jen et al. (2004) identified homozygosity for a splice donor site mutation in the first position of intron 13 of the ROBO3 gene in which G was converted to A (IVS13+1G-A). This mutation in the Fn3 II domain was expected to result in premature termination of the protein. The mutation was not identified in 93 control samples.
In a boy with horizontal gaze palsy with progressive scoliosis-1 (HGPPS1; 607313), who was born of nonconsanguineous parents of Irish and German descent, Chan et al. (2006) identified compound heterozygosity for 2 different 2-bp deletions, 1844delCA and 1886delTT (608630.0012), both in exon 12 of the ROBO3 gene and both predicted to cause a frameshift and premature stop codon, after 23 and 9 altered amino acids, respectively. The mother, who had mild scoliosis not requiring medical treatment, was heterozygous for 1844delCA and the unaffected father was heterozygous for 1886delTT; neither mutation was present on 174 control chromosomes of mixed ethnicity.
For discussion of the 2-bp deletion in the ROBO3 gene (1886delTT) that was found in compound heterozygous state in a patient with horizontal gaze palsy with progressive scoliosis-1 (HGPPS1; 607313) by Chan et al. (2006), see 608630.0011.
In a girl with horizontal gaze palsy with progressive scoliosis-1 (HGPPS1; 607313) who was born of nonconsanguineous parents of English/Irish and Acadian descent, Chan et al. (2006) identified compound heterozygosity for a 733C-T transition in exon 4 and a 2317C-T transition (608630.0014) in exon 15 of the ROBO3 gene. The former was predicted to result in an arg245-to-trp (R245W) substitution between the second and third immunoglobulin-like motifs, and the latter was predicted to result in a gln773-to-ter (Q773X) substitution in the third fibronectin-like motif. The father was heterozygous for R245W and the mother for Q773X; neither mutation was present on 174 control chromosomes of mixed ethnicity.
For discussion of the gln773-to-ter (Q773X) mutation in the ROBO3 gene that was found in compound heterozygous state in a patient with horizontal gaze palsy with progressive scoliosis-1 (HGPPS1; 607313) by Chan et al. (2006), see 608630.0013.
Chan, W.-M., Traboulsi, E. I., Arthur, B., Friedman, N., Andrews, C., Engle, E. C. Horizontal gaze palsy with progressive scoliosis can result from compound heterozygous mutations in ROBO3. J. Med. Genet. 43: e11, 2006. Note: Electronic Article. [PubMed: 16525029] [Full Text: https://doi.org/10.1136/jmg.2005.035436]
Gross, M. B. Personal Communication. Baltimore, Md. 11/30/2016.
Jaworski, A., Tom, I., Tong, R. K., Gildea, H. K., Koch, A. W., Gonzalez, L. C., Tessier-Lavigne, M. Operational redundancy in axon guidance through the multifunctional receptor Robo3 and its ligand NELL2. Science 350: 961-965, 2015. [PubMed: 26586761] [Full Text: https://doi.org/10.1126/science.aad2615]
Jen, J. C., Chan, W.-M., Bosley, T. M., Wan, J., Carr, J. R., Rub, U., Shattuck, D., Salamon, G., Kudo, L. C., Ou, J., Lin, D. D. M., Salih, M. A. M., and 23 others. Mutations in a human ROBO gene disrupt hindbrain axon pathway crossing and morphogenesis. Science 304: 1509-1513, 2004. [PubMed: 15105459] [Full Text: https://doi.org/10.1126/science.1096437]
Sabatier, C., Plump, A. S., Ma, L., Brose, K., Tamada, A., Murakami, F., Lee, E. Y.-H. P., Tessier-Lavigne, M. The divergent Robo family protein Rig-1/Robo3 is a negative regulator of Slit responsiveness required for midline crossing by commissural axons. Cell 117: 157-169, 2004. [PubMed: 15084255] [Full Text: https://doi.org/10.1016/s0092-8674(04)00303-4]
Stein, E., Tessier-Lavigne, M. Hierarchical organization of guidance receptors: silencing of netrin attraction by Slit through a Robo/DCC receptor complex. Science 291: 1928-1938, 2001. Note: Expression of Concern: Science 378: 1284 only, 2022. [PubMed: 11239147] [Full Text: https://doi.org/10.1126/science.1058445]
Yuan, S.-S. F., Cox, L. A., Dasika, G. K., Lee, E. Y.-H. P. Cloning and functional studies of a novel gene aberrantly expressed in RB-deficient embryos. Dev. Biol. 207: 62-75, 1999. [PubMed: 10049565] [Full Text: https://doi.org/10.1006/dbio.1998.9141]