Abstract
The aim of this study is to shed light on the functional role of slc7a6os, a gene highly conserved in vertebrates. The Danio rerio slc7a6os gene encodes a protein of 326 amino acids with 46% identity to human SLC7A6OS and 14% to Saccharomyces cerevisiae polypeptide Iwr1. Yeast Iwr1 specifically binds RNA pol II, interacts with the basal transcription machinery and regulates the transcription of specific genes. In this study we investigated for the first time the biological role of SLC7A6OS in vertebrates. Zebrafish slc7a6os is a maternal gene that is expressed throughout development, with a prevalent localization in the developing central nervous system (CNS). The gene is also expressed, although at different levels, in various tissues of the adult fish. To determine the functional role of slc7a6os during zebrafish development, we knocked-down the gene by injecting a splice-blocking morpholino. At 24 hpf morphants show morphological defects in the CNS, particularly the interface between hindbrain and midbrain is not well-defined. At 28 hpf the morpholino injected embryos present an altered somite morphology and appear partially or completely immotile. At this stage the midbrain, hindbrain and cerebellum are compromised and not well defined compared with control embryos. The observed alterations persist at later developmental stages. Consistently, the expression pattern of two markers specifically expressed in the developing CNS, pax2a and neurod, is significantly altered in morphants. The co-injection of embryos with synthetic slc7a6os mRNA, rescues the morphant phenotype and restores the wild type expression pattern of pax2a and neurod. Our data suggest that slc7a6os might play a critical role in defined areas of the developing CNS in vertebrates, probably by regulating the expression of key genes.
Highlights
Thirteen years after the sequencing of the human genome, the function of a significant percentage of our genes remains unknown
A subsequent in silico analysis allowed us to determine that SLC7A6OS is highly conserved in vertebrates and that homologous sequences can be found in eukaryotic model organisms such as Drosophila melanogaster, Caenorhabditis elegans, Saccharomyces cerevisiae and Arabidopsis thaliana (Fig. 1A)
Previous experiments demonstrated that the yeast homolog IWR1 encodes a protein that interacts with RNA polymerases and positively or negatively affects the expression of several genes
Summary
Thirteen years after the sequencing of the human genome, the function of a significant percentage of our genes remains unknown. The novel gene that we named SLC7A6OS (solute carrier family 7, member 6 opposite strand) is conserved in eukaryotes and the main clues about its biological function come from studies on the yeast Iwr homolog. Studies with high-throughput mass spectrometry conducted in S. cerevisiae led to the identification of a novel factor that binds to the polymerase II complex, namely Iwr1 [3]. In the cytoplasm Iwr binds only to the fully assembled RNA pol-II at the level of the active cleft, involving contacts with both Rpb and Rpb subassemblies [7]. Iwr binding between the large Pol II subunits may sense complete Pol II assembly and limit nuclear import to functional Pol II. Iwr can bind and import another Pol II complex into the nucleus, closing the cycle
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