Disease relevance of En1

• This rapid induction of cell death in mDA neurons suggests that the engrailed genes participate directly in the regulation of apoptosis, a proposed mechanism for Parkinson's disease [1].
• Inhibition of En-1 by antisense targeting during this period resulted in embryos with craniofacial abnormalities, specifically loss of mid- and hindbrain tissue and hypoplasia in associated neural crest derived areas such as the face and first and second pharyngeal arches [2].
• A reduction in calvarial membranous bone deposition and mineralization (osteopenia) is coupled to enhanced osteolytic resorption in En1 mutants [3].
• In addition, we demonstrate that En1 regulates pathfinding and fasciculation during the second phase of EN1 axon growth in the ventrolateral funiculus (VLF); however, En1 is not required for the early specification of ventral interneuron cell types in the embryonic spinal cord [4].
• Analysis of poly(A)+ RNA extracted from teratocarcinoma cells and whole mouse embryos demonstrates that the conserved homeo box region of Mo-en.1 is expressed differentially during mouse embryogenesis [5].

Psychiatry related information on En1

• Using established protocols, we show that, compared with their wild-type littermates, En1+/- mice have impaired motor skills, an anhedonic-like behavior, and an enhanced resignation phenotype; they perform poorly in social interactions [6].

High impact information on En1

• Evidence for this parallel pathway emerged from an analysis of the induction of ventral progenitors that express the Dbx homeodomain proteins and of Evx1/2 (V0) and En1 (V1) neurons [7].
• By examining embryonic expression of the mouse engrailed (En) genes, from 8.0 to 9.5 days postcoitum, we demonstrate that Wnt-1 primarily regulates midbrain development [8].
• The midbrain-hindbrain phenotype of Wnt-1-/Wnt-1- mice results from stepwise deletion of engrailed-expressing cells by 9.5 days postcoitum [8].
• Thus, the observed neonatal phenotype is explained by a series of early events, within 48 hr of neural plate induction, that leads to a complete loss of En domains in the anterior central nervous system [8].
• Mo-en.1 has been mapped to chromosome 1, indicating it is not linked to other homeo box sequences that have been mapped in the mouse genome [5].

Chemical compound and disease context of En1

• However, bromodeoxyuridine-defined arterial SMC proliferation, neointima formation, medial hyperplasia, and arterial remodeling were markedly decreased in mice expressing arterial SMC-restricted Myb-Engrailed after arterial injury [9].

Biological context of En1

• Moreover, transcription factors En1 and Pax2 were also downregulated prior to the 4-somite stage, whereas Gbx2 downregulation occurred at the 4-somite stage [10].
• In mutant mice homozygous null for En1 and En2, the neurons are generated in the ventral midbrain, become postmitotic, and begin to express their neurotransmitter phenotype [11].
• The homeobox transcription factors engrailed 1 and engrailed 2 are expressed by this neuronal population from early in development to adulthood [1].
• Engrailed genes are cell-autonomously required to prevent apoptosis in mesencephalic dopaminergic neurons [1].
• Furthermore, using in vitro cell mixing experiments and RNA interference on primary cell culture of ventral midbrain we were able to show that the demise of mDA neurons in the mutant mice is due to a cell-autonomously requirement of the engrailed genes and not a result of the missing mid-hindbrain tissue [1].

Anatomical context of En1

• Here we investigate whether the caudal limit of Otx2 expression is instrumental in positioning the isthmic organizer and in specifying midbrain versus hindbrain fate, by ectopically expressing Otx2 in the presumptive anterior hindbrain using a knock-in strategy into the En1 locus [12].
• In contrast, expression of Drosophila en in the embryonic limbs of En1 mutants does not lead to repression of Wnt7a in the embryonic ventral ectoderm or full rescue of the embryonic dorsal/ventral patterning defects [13].
• Here we provide evidence that V1 interneurons (INs), an embryonic class of interneurons that transiently express the En1 transcription factor, differentiate as local circuit inhibitory interneurons and form synapses with motor neurons [14].
• Together, these results show that Pax6 and En1 have essential roles in establishing the recurrent inhibitory circuit between motor neurons and Renshaw cells [14].
• To further investigate the role En plays in dorsoventral patterning and AER formation, we have used the replication competent retroviral vector, RCAS, to mis-express mouse En-1 in the early chick limb bud [15].

Associations of En1 with chemical compounds

• The En gradient also correlates with the expression of two putative retinal axon-guidance molecules, RAGS and ELF-1, which are Eph-like receptor tyrosine kinase ligands that may function in the establishment of retinotopic projections by excluding temporal axons from the caudal tectum [16].
• These include the homeobox transcription factors engrailed and Ptx-3 as well as aldehyde dehydrogenase 2, here defined as the earliest marker identified in developing DA cells, expressed already in mitotic DA progenitors [17].
• However, mRNA levels of genes encoding synaptophysin and the 160 kDa neurofilament protein were increased by high LiCl concentrations, whereas mRNA levels of mash-1 and Engrailed-1 were decreased, suggesting a specific influence of lithium on neuronal differentiation [18].
• From linkage analyses of the three-point cross test using Elo and En-1 as marker genes, the bilirubin UDPGT gene was mapped at position 37 on chromosome 1 [19].
• In a recent gene-trap screen, we identified the gene coding for Epidermal Bullous Pemphigoid Antigen 1 (BPAG1) as a putative transcriptional target of Engrailed and of other homeoproteins with a glutamine in position 50 of their homeodomain [20].

Regulatory relationships of En1

• These results strongly support the idea that, in its normal domain of expression, En-1 represses Wnt7a-mediated dorsal differentiation by limiting the expression of Wnt7a to the dorsal ectoderm [15].
• Pax6 defines the di-mesencephalic boundary by repressing En1 and Pax2 [21].
• To achieve this, Otx2 was inactivated by Cre recombinase under the transcriptional control of En1 [22].
• Fibroblast growth factor-8 expression is regulated by intronic engrailed and Pbx1-binding sites [23].
• Conversely, misexpression of Evx1 represses En1, suggesting that Evx1 may suppress the V1 interneuron differentiation program [24].

Other interactions of En1

• Since E9.5 En1/2 double mutants lack the mid/hindbrain region, forebrain mutant explants were treated with FGF8 and, significantly, the EN transcription factors were found to be required for induction of Pax5 [25].
• An almost identical phenotype is found in mutant mice null for Wnt1, indicating that the engrailed genes provide essential positional information for the development of the two nuclei during early embryogenesis [26].
• En1 and En2 act upon at least two steps of the differentiation of mesDA neurons [11].
• Pax6 and engrailed 1 regulate two distinct aspects of renshaw cell development [14].
• Expression and mutation analyses in mice suggest that the homeobox-containing gene Engrailed (En) plays a role in dorsoventral patterning of the limb [15].

Analytical, diagnostic and therapeutic context of En1

• Regions of the mouse and human genomes with strong homology to the Drosophila engrailed gene have been identified by Southern blot analysis [5].
• To determine whether these contrasting phenotypes reflect differences in temporal expression or biochemical activity of the En proteins, En-1 coding sequences were replaced with En-2 sequences by gene targeting [27].
• The antiserum detects both the En-1 and En-2 proteins in mouse, chick and Xenopus embryos by Western blot analysis [28].
• In heterotopic transplantation experiments, En protein expression correlates well with the subsequent gradient of cytoarchitecture as well as the pattern of retinotectal projections [16].
• This is further confirmed by DNase I footprinting and electrophoretic mobility shift assays that reveal, within the cloned BPAG1e promoter, several sites of direct interaction with EnHD and Engrailed [20].

References