NCBI Summary:
This gene encodes a key mitochondrial transcription factor containing two high mobility group motifs. The encoded protein also functions in mitochondrial DNA replication and repair. Sequence polymorphisms in this gene are associated with Alzheimer's and Parkinson's diseases. There are pseudogenes for this gene on chromosomes 6, 7, and 11. Alternative splicing results in multiple transcript variants. [provided by RefSeq, Aug 2012]
General function
DNA binding, Transcription factor
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Cellular localization
Mitochondrial
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Ovarian function
Oocyte maturation, Early embryo development
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Effect of aging on mitochondria and metabolism of bovine granulosa cells. Nagata S et al. (2020) This study investigated the effect of aging on mitochondria in granulosa cells (GCs) collected from the antral follicles of young and aged cows (25-50 months and over 140 months in age, respectively). When GCs were cultured under 20% O2 for 4 days, mitochondrial DNA copy number (Mt-number), determined by real-time PCR, increased throughout the culture period, and the extent of increase was greater in the GCs of young cows than in those of old cows. In a second experiment, GCs were cultured under 20% O2 for 24 h. Protein levels of TOMM20 and TFAM in GCs were lower in aged cows than in young cows, and the amount of reactive oxygen species and the mitochondrial membrane potential were higher, whereas ATP content and proliferation activity were lower, respectively. Glucose consumption and lactate production were higher in the GCs of aged cows than in those of young cows. When GCs were cultured under 5% or 20% O2 for 24 h, low O2 decreased ATP content and increased glucose consumption in GCs of both age groups compared with high O2; however, low O2 decreased the Mt-number only in the GCs of young cows. In conclusion, we show that aging affects mitochondrial quantity, function, and response to differential O2 tensions in GCs.////////////////// Expression of mitochondrial transcription factor A (TFAM) during porcine gametogenesis and preimplantation embryo development. Antelman J et al. Mitochondrial transcription factor A (TFAM) is responsible for stability, maintenance, and transcriptional control of mitochondrial DNA (mtDNA). We have studied the expression and distribution of TFAM in the gametes and preimplantation embryos of the domestic pig (Sus scrofa). We hypothesized that TFAM is not present in the boar sperm mitochondria to reduce the possibility of paternal mtDNA propagation in the progeny. In contrast, we anticipated that Tfam gene is expressed in a developmental stage-dependent manner in porcine oocytes and embryos. The appropriate TFAM band of 25 kDa was detected by Western blotting in ejaculated boar spermatozoa, as well as in porcine oocytes and zygotes. Boar sperm extracts also displayed several bands >25 kDa suggestive of post-translational modification by ubiquitination, confirmed by affinity purification of ubiquitinated proteins. TFAM immunoreactivity was relegated to the sperm tail principal piece and sperm head in fully differentiated spermatozoa. The content of Tfam mRNA increased considerably from the germinal vesicle to blastocyst stage and also between in vitro fertilized and cultured blastocysts compared to in vivo-derived blastocysts. TFAM protein accumulated in the oocytes during maturation and was reduced by proteolysis after fertilization. This pattern was not mirrored in parthenogenetically activated oocytes and zygotes reconstructed by SCNT, suggesting deviant processing of TFAM protein and transcript after oocyte/embryo manipulation. Thus, TFAM may exert a critical role in porcine gametogenesis and preimplantation embryo development. Altogether, our data on the role of TFAM in mitochondrial function and inheritance have broad implications for cell physiology and evolutionary biology. J. Cell. Physiol. (c) 2008 Wiley-Liss, Inc.
Expression regulated by
Comment
Effects of NRF1 on steroidogenesis and apoptosis in goat luteinized granulosa cells. Zhang GM et al. (2017) During goat follicular development, abnormal expression of nuclear respiratory factor 1 (NRF1) in granulosa cells may drive follicular atresia with unknown regulatory mechanisms. In this study, we investigated the effects of NRF1 on steroidogenesis and cell apoptosis by overexpressing or silencing it in goat luteinized granulosa cells (LGCs). Results showed that knockdown of NRF1 expression significantly inhibited the expression of STAR and CYP19A1, which are involved in sex steroid hormones synthesis, and led to lower estrogen levels. Knockdown of NRF1 resulted in an increased percentage of apoptosis, probably due to the release of cytochrome c from mitochondria, accompanied by upregulating mRNA and protein levels of apoptosis-related markers BAX, caspase 3 and caspase 9. These data indicate that NRF1 might be related with steroidogenesis and cell apoptosis. Furthermore, NRF1 silence reduced mitochondrial transcription factor A (TFAM) transcription activity, mtDNA copy number and ATP level. Simultaneously, knockdown of NRF1 suppressed the transcription and translation levels of SOD, GPx and CAT, decreased glutathione level and increased 8-OHdG level. However, the overexpression of NRF1 in LGCs or gain of TFAM in NRF1 silenced LGCs increased the expression of genes involved in mitochondrial function and biogenesis, and elevated the antioxidant stress system and steroids synthesis. Taken together, aberrant expression of NRF1 could induce mitochondrial dysfunction and disturb the cellular redox balance, which lead to disturbance of steroid hormone synthesis, and trigger LGC apoptosis through the mitochondria-dependent pathway. These findings will be helpful for understanding the role of NRF1 in goat ovarian follicular development and atresia.//////////////////
Effect of oxidative stress during repeated ovulation on the structure and functions of the ovary, oocytes, and their mitochondria. Miyamoto K et al. We previously reported that superoxide generated in the ovary induces apoptosis of granulosa cells to break down follicular walls, thereby supporting ovulation in rodents, and suggested that oxidative stress underlies the mechanism of ovarian aging. To test this hypothesis, we successfully induced ovulation repeatedly in mice by sequentially administrating pregnant mare serum gonadotropin, human chorionic gonadotropin, and prostaglandin F2alpha. Kinetic analysis revealed that the number of ovulated oocytes decreased significantly with repeated cycles of ovulation with a concomitant decrease in the gene expression of mitochondrial transcription factor A and nuclear respiratory factor 1 and an increase in oocytes having abnormally distributed mitochondria. Repeated ovulation decreased the amounts of mitochondrial DNA and increased 8-hydroxydeoxyguanosine in oocytes. Cell culture analysis of the in vivo fertilized oocytes revealed that their maturation from two cells to blastocyst was inhibited significantly by repeated ovulation. All these events induced by repeated ovulation were suppressed by oral administration of L-carnitine. These results suggest that oxidative stress associated with ovulation underlies the mechanism of ovarian aging and that L-carnitine may have therapeutic potential in patients with infertility and increased incidence of aneuploidy and to suppress impaired maturation of zygotes frequently observed in childbearing at an advanced age.
Ovarian localization
Oocyte
Comment
Comparison of Mitochondrial-Related Transcriptional Levels of TFAM, NRF1 and MT-CO1 Genes in Single Human Oocytes at Various Stages of the Oocyte Maturation. Ghaffari Novin M et al. (2015) The aim of the current study was to assess the mRNA levels of two mitochondria-related genes, including nuclear-encoded NRF1 (nuclear respiratory factor 1), mitochondrial transcription factor A (TFAM), and mitochondrial-encoded cytochrome c oxidase subunit 1 (MT-CO1) genes in various stages of the human oocyte maturation. Oocytes were obtained from nine infertile women with male factor undergoing in vitro fertilization (IVF)/intra-cytoplasmic sperm injection protocol. Mitochondrial-related mRNA levels were performed by single-cell TaqMan real-time PCR. the expression level of the target genes was low at the germinal vesicle stage (P>0.05). Although the mRNA level of NRF1gene remained stable in metaphase I, the mRNA level of TFAM and MT-CO1 increased significantly (P<0.05).In metaphase II, the expression level of all genes increased compared to metaphase I (P<0.05). The overexpression levels of NRF1, TFAM, and MT-CO1 genes are related to the oocyte maturation. Therefore, the current study could be used clinically to improve the success rate of IVF.//////////////////
Lee SH, et al reported the expression of the mitochondrial ATPase6 gene and Tfam in Down syndrome.
The authors investigated the expression of the mitochondrial ATPase6 gene whose product is active in oxidative phosphorylation (OXPHOS), and compared it to the expression of Tfam, an important regulator of the transcription and replication of mtDNA. The aim was to examine a possible relation between mitochondrial gene expression and Down syndrome. The expression of ATPase6 and Tfam was analyzed by RT-PCR amplification of the mRNA in cultured amniocytes from Down syndrome and normal fetuses. The band intensities obtained were normalized against those of HPRT. The Down syndrome fetuses were found to have lower ATPase6 and Tfam expression than the normal fetuses. This finding suggests that mitochondrial dysfunction resulting from decreased ATPase6 and Tfam expression during meiotic oocyte maturation of oocytes might affect ATP generation and cause the nondisjunctional error. Hence this study suggests that mitochondrial dysfunction may be associated with the developmental mechanism of Down syndrome.
Follicle stages
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Phenotypes
Mutations
3 mutations
Species: mouse
Mutation name: None
type: null mutation fertility: infertile - ovarian defect Comment: The Role of Mitochondrial DNA Copy Number in Mammalian Fertility. Wai T et al. Mammalian mitochondrial DNA (mtDNA) is a small, maternally inherited genome that codes for 13 essential proteins in the respiratory chain. Mature oocytes contain more than 150,000 copies of mtDNA, at least an order of magnitude greater than most somatic cells, but sperm contain only about 100 mtDNAs. Mitochondrial oxidative phosphorylation has been suggested to be an important determinant of oocyte quality and sperm motility; however, the functional significance of the high mtDNA copy number in oocytes and the low copy number in sperm remains unclear. To investigate the effects of mtDNA copy number on fertility we genetically manipulated mtDNA copy number in the mouse by deleting one copy of Tfam, an essential component of the mitochondrial nucleoid, at different stages of germline development. We show that males can tolerate at least a three-fold reduction in mtDNA copy number in their sperm without impaired fertility, and in fact they preferentially transmit a deleted Tfam allele. Surprisingly, oocytes with as few as 4,000 copies of mtDNA can be fertilized and progress normally through pre-implantation development to the blastocyst stage, but there is a critical post-implantation developmental threshold of 40-50,000 copies of mtDNA in the mature oocyte. These observations suggest that the high mtDNA copy number in the mature oocyte is a genetic device, designed to distribute mitochondria and mtDNAs to the cells of the early post-implantation embryo before mitochondrial biogenesis and mtDNA replication resumes, whereas down-regulation of mtDNA copy number is important for normal sperm function.
Species: human
Mutation name: None
type: naturally occurring fertility: subfertile Comment: Expression of the mitochondrial ATPase6 gene and Tfam in Down syndrome. Lee SH et al. We investigated the expression of the mitochondrial ATPase6 gene whose product is active in oxidative phosphorylation (OXPHOS), and compared it to the expression of Tfam, an important regulator of the transcription and replication of mtDNA. Our aim was to examine a possible relation between mitochondrial gene expression and Down syndrome. The expression of ATPase6 and Tfam was analyzed by RT-PCR amplification of the mRNA in cultured amniocytes from Down syndrome and normal fetuses. The band intensities obtained were normalized against those of HPRT. The Down syndrome fetuses were found to have lower ATPase6 and Tfam expression than the normal fetuses. This finding suggests that mitochondrial dysfunction resulting from decreased ATPase6 and Tfam expression during meiotic oocyte maturation of oocytes might affect ATP generation and cause the nondisjunctional error. Hence this study suggests that mitochondrial dysfunction may be associated with the developmental mechanism of Down syndrome.
Species: mouse
Mutation name: type: targeted overexpression fertility: fertile Comment: Mitochondrial transcription factor A regulates mtDNA copy number in mammals. Ekstrand MI et al. (2004) Mitochondrial DNA (mtDNA) copy number regulation is altered in several human mtDNA-mutation diseases and it is also important in a variety of normal physiological processes. Mitochondrial transcription factor A (TFAM) is essential for human mtDNA transcription and we demonstrate here that it is also a key regulator of mtDNA copy number. We initially performed in vitro transcription studies and determined that the human TFAM protein is a poor activator of mouse mtDNA transcription, despite its high capacity for unspecific DNA binding. Next, we generated P1 artificial chromosome (PAC) transgenic mice ubiquitously expressing human TFAM. The introduced human TFAM gene was regulated in a similar fashion as the endogenous mouse Tfam gene and expression of the human TFAM protein in the mouse did not result in down-regulation of the endogenous expression. The PAC-TFAM mice thus had a net overexpression of TFAM protein and this resulted in a general increase of mtDNA copy number. We used a combination of mice with TFAM overexpression and TFAM knockout and demonstrated that mtDNA copy number is directly proportional to the total TFAM protein levels also in mouse embryos. Interestingly, the expression of human TFAM in the mouse results in up-regulation of mtDNA copy number without increasing respiratory chain capacity or mitochondrial mass. It is thus possible to experimentally dissociate mtDNA copy number regulation from mtDNA expression and mitochondrial biogenesis in mammals in vivo. In conclusion, our results provide genetic evidence for a novel role for TFAM in direct regulation of mtDNA copy number in mammals.//////////////////