HGNC Approved Gene Symbol: EN1
Cytogenetic location: 2q14.2 Genomic coordinates (GRCh38): 2:118,842,171-118,847,648 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 2q14.2 | ?ENDOVE syndrome, limb-brain type | 619218 | Autosomal recessive | 3 |
In Drosophila, the 'engrailed' (en) homeobox protein plays an important role during development in segmentation, where it is required for the formation of posterior compartments. Logan et al. (1989) isolated the human homologs of the mouse homeobox-containing genes En1 and En2 (131310), which show homology to the Drosophila en gene. Logan et al. (1992) isolated human and chicken genomic clones of the EN1 and EN2 genes. The deduced 392-amino acid human EN1 protein is 95% identical to mouse En1. By sequence analysis, the authors determined that En proteins from various species contain 5 distinct conserved subregions. Logan et al. (1992) noted that expression studies have suggested that engrailed may function early in organizing the preblastoderm and later in neurogenesis.
Logan et al. (1992) demonstrated that as in mouse and chicken, the predicted coding region of the human EN1 gene is interrupted by a single intron.
Martin et al. (1990) mapped the En1 gene to mouse chromosome 1, approximately 0.28 cM distal to the 'dominant hemimelia' (Dh) gene, and the En2 gene to mouse chromosome 5, approximately 1.1 cM proximal to the 'hemimelic extra-toes' (Hx) gene. They excluded both of these genes as the site of the mutations responsible for Dh and Hx. They suggested that En1/Dh and En2/Hx represent paralogous linkage groups that evolved following duplication of a common ancestral chromosome segment.
By Southern analysis of mouse-human somatic cell hybrids, Logan et al. (1989) mapped the human EN1 gene to chromosome 2. Using a mapping panel of rodent/human cell hybrids containing different regions of chromosome 2 and a lymphoblastoid cell line with an interstitial deletion, del(2)(q21-q23.2), Kohler et al. (1993) refined the regional assignment of EN1 to 2q13-q21. They stated that this increased to 22 the number of known genes on 2q that have homologs in the proximal region of mouse chromosome 1. By fluorescence in situ hybridization, Matsui et al. (1993) further refined the EN1 gene map position to 2q14.
In a 14-month-old boy with possible PEHO syndrome (260565) from a consanguineous Pakistani family, Barber et al. (2006) identified a heterozygous deletion of 2q14.1-q14.2, a region with a minimum of 20 genes including EN1. However, the same deletion was found in his phenotypically normal father and brother. The authors noted that this deletion overlapped with a previously reported transmitted deletion of 2q13-q14.1 that had no phenotypic consequences (Sumption and Barber, 2001). The deleted regions contain a total of 32 genes and comprise the final 5.25 Mb of the ancestral chromosome 2B from which chromosome 2 was formed in man. Barber et al. (2006) concluded that heterozygous deletions of regions of low gene density are compatible with a normal phenotype.
ENDOVE Syndrome, Limb-Brain Type
In a 3-year-old Brazilian girl who had mesomelia of the lower extremities with hand, foot, and brain anomalies (ENDOVESLB; 619218), Allou et al. (2021) identified homozygosity for a 1-bp duplication in the EN1 gene (131290.0001).
Associations Pending Confirmation
For discussion of a possible association between a noncoding single-nucleotide polymorphism (SNP) near the EN1 gene and bone mineral density, see 166710.
The related mouse genes En1 and En2 are expressed from the 1- and approximately 5-somite stages, respectively, in a similar presumptive mid-hindbrain domain. However, mutations in En1 and En2 produced different phenotypes: En1 mutant mice die at birth with a large mid-hindbrain deletion, whereas En2 mutants survive with cerebellar defects. To determine whether these contrasting phenotypes reflect differences in temporal expression or biochemical activity of the En proteins, Hanks et al. (1995) replaced En1 coding sequences with En2 sequences in transgenic mice by gene targeting. The En2 sequences rescued all En1 mutant defects, demonstrating that the difference between En1 and En2 stems from their divergent expression patterns.
Wurst et al. (1994) generated mice homozygous for a targeted deletion of the En1 homeobox. En1 mutant mice died shortly after birth and exhibited multiple developmental defects. The pattern of defects suggested a cell-autonomous role for En1 in generation and/or survival of mid-hindbrain precursor cells and also a non-cell-autonomous role in signaling normal development of the limbs and possibly sternum.
Loomis et al. (1996) analyzed the effects of an induced null mutation in the mouse engrailed-1 gene on ventral limb patterning. That the gene is essential was indicated by the finding that the null mice showed dorsal transformations of ventral paw structures, as well as subtle alterations along the proximal-distal limb axis.
For a review of the role of this gene in limb development, see Johnson and Tabin (1997).
Sgado et al. (2006) found that mice heterozygous null for En1 and homozygous null for En2 (En1 +/- and En2 -/-) were viable and fertile, but they showed an adult phenotype that resembled key pathologic features of Parkinson disease (168600). Mutant mice showed progressive degeneration of dopaminergic neurons in the substantia nigra, which led to diminished storage and release of dopamine in the caudate putamen, motor deficits similar to akinesia and bradykinesia, and lower body weight.
In a Drosophila model of HD (143100) with mutant human HTT (613004), Mugat et al. (2008) found that expression of engrailed was able to prevent aggregation of polyQ-HTT by activating transcription of endogenous wildtype htt.
Using an En1(cre/flox) mouse model, Zheng et al. (2015) observed that conditional loss of En1 results in low bone mass, probably as a consequence of high bone turnover.
Based on their studies of patients with ENDOVESL (see 619217), Allou et al. (2021) hypothesized the existence of a regulatory region controlling En1 expression in the limb. They performed capture Hi-C, a technology to quantify chromatin contacts genomewide, in mouse limb buds from embryonic day (E) 9.5 and found that a region corresponding to the 27-kb minimal critical region (MCR) in the human patients is located within an approximately 650-kb topologically associated domain (TAD) that includes En1. Further analysis revealed the presence of a 4-exon long noncoding RNA (lncRNA) transcript within the MCR, with a transcriptional start site (TSS) located approximately 251 kb downstream of the 3-prime end of En1. The authors designated this transcript 'Maenli,' for 'master activator of engrailed-1 in the limb.' Single-cell RNA-seq from E9.5 and E10.5 mouse limbs showed that Maenli RNA was present almost exclusively in the ectoderm cluster, overlapping En1 expression. Using marker genes as identifiers, the authors demonstrated that Maenli expression is restricted to En1-expressing domains (apical ectodermal ridge and ventral ectoderm). Generation of mice with a deletion encompassing the Maenli TSS resulted in a more than 98% reduction in expression of Maenli and En1 in the developing limb and a double dorsal-limb phenotype, confirming that the Maenli locus is causal for the limb malformations in mice that resemble the human phenotype. Further experiments demonstrated that inactivation of Maenli on 1 allele could not be rescued by Maenli transcripts generated from the sister allele; thus, activation of En1 in the limb is dependent on transcription of Maenli in cis. Analysis of 3D chromatin folding suggested that Maenli transcription in cis helps to establish a permissive chromatin environment at the En1 locus and its surrounding regulatory landscape, thus allowing access to transcription factors required for En1 activation and ventral ectodermal cell-fate decisions.
In a 3-year-old Brazilian girl (patient 4), born of first-cousin parents, who had mesomelia of the lower extremities with hand, foot, and brain anomalies (ENDOVESLB; 619218), Allou et al. (2021) identified homozygosity for a 1-bp duplication (c.317dupT, NM_001426.3) in the EN1 gene, causing a frameshift predicted to result in a premature termination codon (Ile107HisfsTer39). Her asymptomatic mother was heterozygous for the mutation; DNA analysis was not reported for her unaffected father.
Allou, L., Balzano, S., Magg, A., Quinodoz, M., Royer-Bertrand, B., Schopflin, R., Chan, W.-L., Speck-Martins, C. E., Carvalho, D. R., Farage, L., Lourenco, C. M., Albuquerque, R., and 21 others. Non-coding deletions identify Maenli lncRNA as a limb-specific En1 regulator. Nature 592: 93-98, 2021. [PubMed: 33568816] [Full Text: https://doi.org/10.1038/s41586-021-03208-9]
Barber, J. C. K., Maloney, V. K., Bewes, B., Wakeling, E. Deletions of 2q14 that include the homeobox engrailed 1 (EN1) transcription factor are compatible with a normal phenotype. Europ. J. Hum. Genet. 14: 739-743, 2006. [PubMed: 16552425] [Full Text: https://doi.org/10.1038/sj.ejhg.5201605]
Hanks, M., Wurst, W., Anson-Cartwright, L., Auerbach, A. B., Joyner, A. L. Rescue of the En-1 mutant phenotype by replacement of En-1 with En-2. Science 269: 679-682, 1995. [PubMed: 7624797] [Full Text: https://doi.org/10.1126/science.7624797]
Johnson, R. L., Tabin, C. J. Molecular models for vertebrate limb development. Cell 90: 979-990, 1997. [PubMed: 9323126] [Full Text: https://doi.org/10.1016/s0092-8674(00)80364-5]
Kohler, A., Logan, C., Joyner, A. L., Muenke, M. Regional assignment of the human homeobox-containing gene EN1 to chromosome 2q13-q21. Genomics 15: 233-235, 1993. [PubMed: 8094370] [Full Text: https://doi.org/10.1006/geno.1993.1045]
Logan, C., Hanks, M. C., Noble-Topham, S., Nallainathan, D., Provart, N. J., Joyner, A. L. Cloning and sequence comparison of the mouse, human, and chicken engrailed genes reveal potential functional domains and regulatory regions. Dev. Genet. 13: 345-358, 1992. [PubMed: 1363401] [Full Text: https://doi.org/10.1002/dvg.1020130505]
Logan, C., Willard, H. F., Rommens, J. M., Joyner, A. L. Chromosomal localization of the human homeo box-containing genes, EN1 and EN2. Genomics 4: 206-209, 1989. [PubMed: 2567700] [Full Text: https://doi.org/10.1016/0888-7543(89)90301-7]
Loomis, C. A., Harris, E., Michaud, J., Wurst, W., Hanks, M., Joyner, A. L. The mouse engrailed-1 gene and ventral limb patterning. Nature 382: 360-363, 1996. [PubMed: 8684466] [Full Text: https://doi.org/10.1038/382360a0]
Martin, G. R., Richman, M., Reinsch, S., Nadeau, J. H., Joyner, A. Mapping of the two mouse engrailed-like genes: close linkage of En-1 to dominant hemimelia (Dh) on chromosome 1 and of En-2 to hemimelic extra-toes (Hx) on chromosome 5. Genomics 6: 302-308, 1990. [PubMed: 2307472] [Full Text: https://doi.org/10.1016/0888-7543(90)90570-k]
Matsui, T., Hirai, M., Hirano, M., Kurosawa, Y. The HOX complex neighbored by the EVX gene, as well as two other homeobox-containing genes, the GBX-class and the EN class, are located on the same chromosomes 2 and 7 in humans. FEBS Lett. 336: 107-110, 1993. [PubMed: 7903253] [Full Text: https://doi.org/10.1016/0014-5793(93)81620-f]
Mugat, B., Parmentier, M.-L., Bonneaud, N., Chan, H. Y. E., Maschat, F. Protective role of engrailed in a Drosophila model of Huntington's disease. Hum. Molec. Genet. 17: 3601-3616, 2008. [PubMed: 18718937] [Full Text: https://doi.org/10.1093/hmg/ddn255]
Sgado, P., Alberi, L., Gherbassi, D., Galasso, S. L., Ramakers, G. M. J., Alavian, K. N., Smidt, M. P., Dyck, R. H., Simon, H. H. Slow progressive degeneration of nigral dopaminergic neurons in postnatal Engrailed mutant mice. Proc. Nat. Acad. Sci. 103: 15242-15247, 2006. [PubMed: 17015829] [Full Text: https://doi.org/10.1073/pnas.0602116103]
Sumption, N. D., Barber, J. C. K. A transmitted deletion of 2q13 to 2q14.1 causes no phenotypic abnormalities. (Letter) J. Med. Genet. 38: 125-126, 2001. [PubMed: 11288713] [Full Text: https://doi.org/10.1136/jmg.38.2.125]
Wurst, W., Auerbach, A. B., Joyner, A. L. Multiple developmental defects in Engrailed-1 mutant mice: an early mid-hindbrain deletion and patterning defects in forelimbs and sternum. Development 120: 2065-2075, 1994. [PubMed: 7925010] [Full Text: https://doi.org/10.1242/dev.120.7.2065]
Zheng, H.-F., Forgetta, V., Hsu, Y.-H., Estrada, K., Rosello-Diez, A., Leo, P. J., Dahia, C. L., Park-Min, K. H., Tobias, J. H., Kooperberg, C., Kleinman, A., Styrkarsdottir, U., and 147 others. Whole-genome sequencing identifies EN1 as a determinant of bone density and fracture. Nature 526: 112-117, 2015. [PubMed: 26367794] [Full Text: https://doi.org/10.1038/nature14878]