E4 Transcription Factor 1 (E4F1) Regulates Sertoli Cell Proliferation and Fertility in Mice

Transcription factor E4F1 as a regulator of cell life and disease progression

E4F transcription factor 1 (E4F1), a member of the GLI-Kruppel family of zinc finger proteins, is now widely recognized as a transcription factor. It plays a critical role in regulating various cell processes, including cell growth, proliferation, differentiation, apoptosis and necrosis, DNA damage response, and cell metabolism. These processes involve intricate molecular regulatory networks, making E4F1 an important mediator in cell biology. Moreover, E4F1 has also been implicated in the pathogenesis of a range of human diseases. In this review, we provide an overview of the major advances in E4F1 research, from its first report to the present, including studies on its protein domains, molecular mechanisms of transcriptional regulation and biological functions, and implications for human diseases. We also address unresolved questions and potential research directions in this field. This review provides insights into the essential roles of E4F1 in human health and disease and may pave the way for facilitating E4F1 from basic research to clinical applications.

Transcription factor E4F1 dictates spermatogonial stem cell fate decisions by regulating mitochondrial functions and cell cycle progression

BACKGROUND

Spermatogonial stem cells (SSCs) provide a foundation for robust and continual spermatogenesis in mammals. SSCs self-renew to maintain a functional stem cell pool and differentiate to supply committed progenitors. Metabolism acts as a crucial determinant of stem cell fates; however, factors linking metabolic programs to SSC development and maintenance are poorly understood.

RESULTS

We analyzed the chromatin accessibility of undifferentiated spermatogonia at the single-cell level and identified 37 positive TF regulators that may have potential roles in dictating SSC fates. The transcription factor E4F1 is expressed in spermatogonia, and its conditional deletion in mouse germ cells results in progressive loss of the entire undifferentiated spermatogonial pool. Single-cell RNA-seq analysis of control and E4f1-deficient spermatogonia revealed that E4F1 acts as a key regulator of mitochondrial function. E4F1 binds to promotors of genes that encode components of the mitochondrial respiratory chain, including Ndufs5, Cox7a2, Cox6c, and Dnajc19. Loss of E4f1 function caused abnormal mitochondrial morphology and defects in fatty acid metabolism; as a result, undifferentiated spermatogonia were gradually lost due to cell cycle arrest and elevated apoptosis. Deletion of p53 in E4f1-deficient germ cells only temporarily prevented spermatogonial loss but did not rescue the defects in SSC maintenance.

CONCLUSIONS

Emerging evidence indicates that metabolic signals dictate stem cell fate decisions. In this study, we identified a list of transcription regulators that have potential roles in the fate transitions of undifferentiated spermatogonia in mice. Functional experiments demonstrated that the E4F1-mediated transcription program is a crucial regulator of metabolism and SSC fate decisions in mammals.

Multi-Level Control of the ATM/ATR-CHK1 Axis by the Transcription Factor E4F1 in Triple-Negative Breast Cancer

E4F1 is essential for early embryonic mouse development and for controlling the balance between proliferation and survival of actively dividing cells. We previously reported that E4F1 is essential for the survival of murine p53-deficient cancer cells by controlling the expression of genes involved in mitochondria functions and metabolism, and in cell-cycle checkpoints, including CHEK1, a major component of the DNA damage and replication stress responses. Here, combining ChIP-Seq and RNA-Seq approaches, we identified the transcriptional program directly controlled by E4F1 in Human Triple-Negative Breast Cancer cells (TNBC). E4F1 binds and regulates a limited list of direct target genes (57 genes) in these cells, including the human CHEK1 gene and, surprisingly, also two other genes encoding post-transcriptional regulators of the ATM/ATR-CHK1 axis, namely, the TTT complex component TTI2 and the phosphatase PPP5C, that are essential for the folding and stability, and the signaling of ATM/ATR kinases, respectively. Importantly, E4F1 also binds the promoter of these genes in vivo in Primary Derived Xenograft (PDX) of human TNBC. Consequently, the protein levels and signaling of CHK1 but also of ATM/ATR kinases are strongly downregulated in E4F1-depleted TNBC cells resulting in a deficiency of the DNA damage and replicative stress response in these cells. The E4F1-depleted cells fail to arrest into S-phase upon treatment with the replication-stalling agent Gemcitabine, and are highly sensitized to this drug, as well as to other DNA-damaging agents, such as Cisplatin. Altogether, our data indicate that in breast cancer cells the ATM/ATR-CHK1 signaling pathway and DNA damage-stress response are tightly controlled at the transcriptional and post-transcriptional level by E4F1.

Cellular and Molecular Insights Into the Etiology of Subfertility/Infertility in Crossbred Bulls (Bos taurus × Bos indicus): A Review

Crossbreeding of indigenous cattle (Bos indicus) with improved (Bos taurus) breeds gained momentum and economic relevance in several countries to increase milk production. While production performance of the crossbred offspring is high due to hybrid vigor, they suffer from a high incidence of reproductive problems. Specifically, the crossbred males suffer from serious forms of subfertility/infertility, which can have a significant effect because semen from a single male is used to breed several thousand females. During the last two decades, attempts have been made to understand the probable reasons for infertility in crossbred bulls. Published evidence indicates that testicular cytology indices, hormonal concentrations, sperm phenotypic characteristics and seminal plasma composition were altered in crossbred compared to purebred males. A few recent studies compared crossbred bull semen with purebred bull semen using genomics, transcriptomics, proteomics and metabolomics; molecules potentially associated with subfertility/infertility in crossbred bulls were identified. Nevertheless, the precise reason behind the poor quality of semen and high incidence of sub-fertility/infertility in crossbred bulls are not yet well defined. To identify the underlying etiology for infertility in crossbred bulls, a thorough understanding of the magnitude of the problem and an overview of the prior art is needed; however, such systematically reviewed information is not available. Therefore, the primary focus of this review is to compile and analyze earlier findings on crossbred bull fertility/infertility. In addition, the differences between purebred and crossbred males in terms of testicular composition, sperm phenotypic characteristics, molecular composition, environmental influence and other details are described; future prospects for research on crossbred males are also outlined.