Regular Article
Spatiotemporal, Allelic, and Enforced Expression ofXimpact,theXenopusHomolog of Mouse Imprinted GeneImpact

https://doi.org/10.1006/bbrc.1999.0297Get rights and content

Abstract

MouseImpactis an imprinted gene encoding an evolutionarily conserved protein of unknown function. We isolated cDNA for theXenopushomolog ofImpact(Ximpact), since the clawed frog not only provides an excellent model for the study of gene function in early development but also allows the generation of interspecific F1 hybrids required for the examination of allelic expression status. The predicted product ofXimpactshows an extreme sequence similarity to those of mouseImpactand its homologs in nematoda, fission yeast, and budding yeast. The transcript ofXimpactis present in oocytes as well as in early embryos, and its spatial distribution is ubiquitous in both embryonic and adult stages. An RT-PCR-RFLP assay using the reciprocal interspecific F1 hybrids and a DNA polymorphism betweenX. laevisandX. borealisshowed thatXimpactis expressed biallelically when analyzed as a whole embryo. Overexpression ofXimpactby RNA microinjection resulted in a higher than normal rate of gastrulation defects, suggesting the need for tight control of its dosage in early development.

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      The N-terminal domain in IMPACT shares sequence similarity with the Gcn2 N-terminus, and also constitutes an RWD domain [62,64]. The gene encoding IMPACT is present in most eukaryotes [64,137,161,163,164]. The IMPACT protein in S. cerevisiae was called Yih1, for yeast Impact homologue [62].

    • Diseases associated with genomic imprinting

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      Citation Excerpt :

      For several species, studies have looked at the expression of orthologs of certain genes known to be imprinted in mammals, typically the canonical pair of imprinted genes Igf2 (insulin-like growth factor type 2) and Igf2r (insulin-like growth factor type 2 receptor). These studies have shown specific genes to be unimprinted in monotremes,9,10,20 amphibians,21 birds,12,13 and fish,22,23 leading some to conclude that imprinting does not exist in those species. However, there have been no systematic efforts to identify imprinted genes in most species, and it remains possible that other genes are imprinted in some or all of those species.

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      Direct sequencing of its cDNA demonstrated biallelic expression of macaque Impact like human IMPACT (Fig. 5). Based on hazardous effects of overexpressed Impact in frog [14] and yeast [15], a paralogous genomic segment but lacking Impact homologue, and elevated expression of Impact in mouse, we previously proposed that segmental duplication [16] followed by enhancement of the promoter activity in the linage to mouse evolved the species-specific solitary imprinting of Impact and suggested that the repeat may play a role in enhancement of expression, thereby contributing to imprinting [17]. To validate this model, we compared the expression level of Impact among mouse, rat, rabbit, pig, macaque, and human by an RT-PCR assay using a single common primer pair designed from the conserved sequences of exon 2 and 5.

    • Budding Yeast GCN1 Binds the GI Domain to Activate the eIF2α Kinase GCN2

      2001, Journal of Biological Chemistry
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      As pointed out previously (15), the GI domain is found in various proteins other than GCN2. They include Impact (a product of an evolutionarily conserved gene that is genetically imprinted in mice) (29-31), AO7 (a RING finger protein interacting with ubiquitin-conjugating enzymes) (32), ARA54 (a coactivator of androgen receptor) (33), YDR152W (a yeast hypothetical protein), YLR419W (a member of the DEAH-box RNA helicase family), and so forth. It remains to be elucidated whether these GI domains also function in protein binding.

    • GI domain-mediated association of the eukaryotic initiation factor 2α kinase GCN2 with its activator GCN1 is required for general amino acid control in budding yeast

      2000, Journal of Biological Chemistry
      Citation Excerpt :

      The GCN1-binding region of YIH1 was mapped to the less conserved N-terminal portion (aa 1–125) but not to the C-terminal region, highly conserved among all members of this family (data not shown). Although no homology had been noted for this N-terminal region, we analyzed it using the PSI-BLAST program (22) to reveal a modest homology between YIH1 and Drosophila GCN2 (23, 24). Based on this alignment and further PSI-BLAST search, we found that three characteristic motif-like sequences connected by spacers of variable lengths are conserved among the homologs of GCN2 and Impact as well as in other proteins of apparently unrelated origins (Fig. 1).

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