Transketolase (EC 2.2.1.1 ) is a thiamine-dependent enzyme that links the pentose phosphate pathway with the glycolytic
pathway. The pentose phosphate pathway is active in most tissues. Its functions are to provide sugar phosphates for
intermediary biosynthesis, especially nucleotide metabolism, and also to generate the biosynthetic reducing power for the
cell in the form of NADPH. Transketolase is directly involved in the branch of the pathway that channels excess sugar
phosphates to glycolysis,
General function
Metabolism, Enzyme, Transferase
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Cellular localization
Cytoplasmic
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Ovarian function
Early embryo development
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Regulation of transketolase like 1 gene expression in the murine one-cell stage embryos. Hamamoto G 2014 et al.
In mice, transcription from the zygotic genome starts at the mid-one-cell stage after fertilization. Previous studies showed that an enhancer is not required for transcription at this stage, and that the enhancer-dependent mechanism of transcription is established during the two-cell stage. However, these results were obtained using reporter gene assays with promoters derived from viruses, rather than from endogenous genes. We conducted a reporter-gene assay using the promoter of Tktl1, which is transcribed after fertilization, to investigate the mechanism regulating gene expression at the one-cell stage. When a plasmid containing the 2467 bp upstream and 25 bp downstream of the Tktl1 transcription start site (TSS) was microinjected into the nuclei of growing oocytes, and one-cell stage and early and late two-cell-stage embryos, transcriptional activity was detected in the one-cell- and two-cell-stage embryos, but not in the oocytes. It was highest at the early two-cell stage and was reduced at the late two-cell stage. The decrease in activity at the late two-cell stage was prevented by inhibiting the second round of DNA replication, suggesting that the transcriptionally repressive state is established during the two-cell stage by a mechanism coupled to DNA replication. When the Tktl1 promoter was deleted to leave 56 bp upstream of the TSS which includes GC and TATA boxes, transcriptional activity was still detected in one-cell-stage embryos, but not early or late two-cell-stage embryos. The core promoter of Tktl1 alone seems to be able to induce basal transcription at the one-cell stage. These results suggest that repressive chromatin is established after fertilization in two steps, which occur during the transition from the one- to two-cell stage and during DNA replication at the two-cell stage.
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Expression regulated by
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Ovarian localization
Oocyte
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Follicle stages
Primordial, Primary, Secondary
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Genomewide discovery and classification of candidate ovarian fertility genes in the mouse. Gallardo TD et al. Female infertility syndromes are among the most prevalent chronic health disorders in women, but their genetic basis remains unknown because of uncertainty regarding the number and identity of ovarian factors controlling the assembly, preservation, and maturation of ovarian follicles. To systematically discover ovarian fertility genes en masse, we employed a mouse model (Foxo3) in which follicles are assembled normally but then undergo synchronous activation. We developed a microarray-based approach for the systematic discovery of tissue-specific genes and, by applying it to Foxo3 ovaries and other samples, defined a surprisingly large set of ovarian factors (n = 348, approximately 1% of the mouse genome). This set included the vast majority of known ovarian factors, 44% of which when mutated produce female sterility phenotypes, but most were novel. Comparative profiling of other tissues, including microdissected oocytes and somatic cells, revealed distinct gene classes and provided new insights into oogenesis and ovarian function, demonstrating the utility of our approach for tissue-specific gene discovery. This study will thus facilitate comprehensive analyses of follicle development, ovarian function, and female infertility. This is an gene expressed in early follicles and high in oocytes but declines by PD14.