Alternative titles; symbols
HGNC Approved Gene Symbol: PKNOX1
Cytogenetic location: 21q22.3 Genomic coordinates (GRCh38): 21:42,974,562-43,033,931 (from NCBI)
PKNOX1 belongs to the 3-amino acid loop extension (TALE) class of homeodomain transcription factors that form transcriptionally active complexes involved in development and organogenesis (Ferretti et al., 2006).
As part of developing a transcript map of human chromosome 21, Chen et al. (1997) used exon trapping to identify portions of genes from chromosome 21-specific cosmids. They identified a trapped exon that is identical to a region of the human expressed sequence tag (EST) L12425. Using the exon and EST as probes, they screened human fetal brain and kidney cDNA libraries and cloned the corresponding gene, which encodes a homeodomain-containing polypeptide of 436 amino acids. Chen et al. (1997) used the EST as a probe for Northern blot analysis and detected transcripts of 2.5 kb and 5 kb in every human tissue examined, including adult heart, brain and brain subregions, placenta, lung, liver, muscle, kidney, and pancreas as well as in several fetal tissues. The gene, designated PBX/knotted-1 homeobox-1 (PKNOX1), has a homeodomain closely related to those of the mammalian PBX family (such as mouse Meis1, 601739) and the plant knotted-1 family (involved in plant development).
By mass spectrometric analysis of a 64-kD protein that copurified with 2 distinct urokinase (PLAU; 191840) enhancer factor-3 (UEF3) complexes from HeLa cell nuclear extracts, followed by screening a HeLa cell cDNA library and 5-prime RACE, Berthelsen et al. (1998) cloned PKNOX1, which they called PREP1. The predicted 436-amino acid protein has a calculated molecular mass of 49 kD. It has 2 regions that share homology with similar regions of MEIS1-related proteins, followed by a 60-amino acid DNA-binding homeodomain.
Chen et al. (1997) used PCR amplification, hybridization, and genetic linkage analysis to map the PKNOX1 gene to chromosome 21q22.3 between markers D21S212 and D21S25 on YAC350F7. By fluorescence in situ hybridization, Berthelsen et al. (1998) mapped the PKNOX1 gene to human chromosome 21q22.3 and mouse chromosome 17B/C.
Two distinct UEF3 complexes, which share a common 64-kD subunit but differ in having either a 50-kD or 40-kD subunit, recognize a TGACAG core DNA sequence. Berthelsen et al. (1998) identified PREP1 as the common 64-kD UEF3 subunit, PBX2 (176311) as the 50-kD subunit, and PBX1 (176310) isoform b (PBX1b) as the 40-kD subunit. Immunoprecipitation analysis confirmed that PREP1 also formed a complex with PBX1 isoform a (PBX1a), and interaction of PREP1 with its UEF3 partners was independent of DNA. Recombinant PREP1 bound to the TGACAG core sequence with low affinity. However, it bound with much higher affinity when it was cotranslated in vitro with either PBX1a, PBX1b, or PBX2, but not when it was mixed with its purified binding partners.
Using suppression subtractive hybridization and quantitative real-time PCR on 12 male Down syndrome (DS; 190685) fetal half-brains and 10 male control fetal half-brains, Sanchez-Font et al. (2003) found that DS brains showed 1.63-fold upregulation of FABP7 (602965), a fatty acid-binding protein involved in development, establishment, and maintenance of the nervous system. Real-time PCR also revealed upregulation of PKNOX1 in DS brains. Recombinant PKNOX1 bound weakly to a PBX/POU site in the FABP7 promoter in vitro, but it robustly activated expression of a reporter containing the PBX/POU site when coexpressed with the reporter in human SH-SY5Y neuroblastoma cells, a source of its PBX binding partners. Sanchez-Font et al. (2003) postulated that dosage imbalance in trisomy 21 that results in overexpression of PKNOX1 may contribute to or even enhance DS-associated neurologic disorders by causing overexpression of FABP7.
Using insertional mutagenesis, Ferretti et al. (2006) created mice homozygous for a hypomorphic Prep1 allele (Prep1 i/i mice). Embryonic day-10.5 (E10.5) Prep1 i/i embryos showed 1.5% of Prep1 mRNA compared with wildtype embryos. Most Prep1 i/i embryos died between E17.5 and birth with overall organ hypoplasia, severe anemia, impaired angiogenesis, and eye abnormalities, particularly in lens and retina. Surviving Prep1 i/i mice had a normal life span, but they showed a defect in T-cell development. Prep1 deficiency decreased protein, but not mRNA, content of the TALE homeobox proteins Pbx1, Pbx2, and Meis1, and it reduced both mRNA and protein content of Pbx3 (176312), Pbx4 (608127), Meis2 (601740), and Meis3 (619443), as well as Cmyb (MYB; 189990).
Fernandez-Diaz et al. (2010) found that lethality in Prep1 -/- mouse embryos was accompanied by apoptosis-induced loss of pluripotent epiblasts, which therefore failed to form anterior visceral endoderm, primitive streak, and differentiated lineages. Simultaneous knockout of p53 (TP53; 191170) partially rescued apoptosis in Prep1 -/- epiblasts, suggesting interaction between Prep1 and p53 in embryonic development. Prep1 was not essential for establishment of embryonic stem cells.
Berthelsen, J., Viggiano, L., Schulz, H., Ferretti, E., Consalez, G. G., Rocchi, M., Blasi, F. PKNOX1, a gene encoding PREP1, a new regulator of Pbx activity, maps on human chromosome 21q22.3 and murine chromosome 17B/C. Genomics 47: 323-324, 1998. [PubMed: 9479508] [Full Text: https://doi.org/10.1006/geno.1997.5086]
Berthelsen, J., Zappavigna, V., Mavilio, F., Blasi, F. Prep1, a novel functional partner of Pbx proteins. EMBO J. 17: 1423-1433, 1998. [PubMed: 9482739] [Full Text: https://doi.org/10.1093/emboj/17.5.1423]
Chen, H., Rossier, C., Nakamura, Y., Lynn, A., Chakravarti, A., Antonarakis, S. E. Cloning of a novel homeobox-containing gene, PKNOX1, and mapping to human chromosome 21q22.3. Genomics 41: 193-200, 1997. [PubMed: 9143494] [Full Text: https://doi.org/10.1006/geno.1997.4632]
Fernandez-Diaz, L. C., Laurent, A., Girasoli, S., Turco, M., Longobardi, E., Iotti, G., Jenkins, N. A., Fiorenza, M. T., Copeland, N. G., Blasi, F. The absence of Prep1 causes p53-dependent apoptosis of mouse pluripotent epiblast cells. Development 137: 3393-3403, 2010. [PubMed: 20826531] [Full Text: https://doi.org/10.1242/dev.050567]
Ferretti, E., Villaescusa, J. C., Di Rosa, P., Fernandez-Diaz, L. C., Longobardi, E., Mazzieri, R., Miccio, A., Micali, N., Selleri, L., Ferrari, G., Blasi, F. Hypomorphic mutation of the TALE gene Prep1 (pKnox1) causes a major reduction of Pbx and Meis proteins and a pleiotropic embryonic phenotype. Molec. Cell. Biol. 26: 5650-5662, 2006. [PubMed: 16847320] [Full Text: https://doi.org/10.1128/MCB.00313-06]
Sanchez-Font, M., Bosch-Comas, A., Gonzalez-Duarte, R., Marfany, G. Overexpression of FABP7 in Down syndrome fetal brains is associated with PKNOX1 gene-dosage imbalance. Nucleic Acids Res. 31: 2769-2777, 2003. [PubMed: 12771203] [Full Text: https://doi.org/10.1093/nar/gkg396]