Papers of the Month
By Gabriel Knudsen, Emilie Mathura, Alicia Richards, Payel Sil, and Salahuddin Syed
NTP finds replacement disinfectant is an irritant
National Toxicology Program scientists found that ortho-phthalaldehyde (OPA), a chemical disinfectant used as an alternative for the germicide glutaraldehyde, has the potential to irritate the lungs, eyes, and skin of exposed rats and mice. The finding suggests that OPA may not be a suitable replacement.
Glutaraldehyde was used for decades to sterilize medical and dental equipment, but the compound was associated with red, itchy skin and occupational asthma in those who handled it. OPA was considered a better option, because of its greater antimicrobial ability and perceived safety. However, whole-body inhalation studies with Harlan Sprague-Dawley rats and B6C3F1/N mice suggested OPA was also associated with health effects.
Researchers exposed the rodents for three months, using differing concentrations of OPA. The rats and mice developed lesions at the sites of contact throughout the respiratory tract, including the nose, larynx, trachea, and lung, as well as the eyes and skin. In general, necrotic lesions occurred at deeper sites within the respiratory tract with increasing concentrations. The authors are concerned about the use of OPA as a replacement for glutaraldehyde as a high-level disinfectant. (PS)
Citation: Catlin NR, Willson CJ, Stout M, Kissling GE, Waidyanatha S, Baker GL, Hayden BK, Wyde M. 2017. Evaluation of the respiratory tract toxicity of ortho-phthalaldehyde, a proposed alternative for the chemical disinfectant glutaraldehyde. Inhal Toxicol 29(9):414–427.
Methionine metabolism important in embryonic development
A research team led by NIEHS scientists showed that methionine metabolism is regulated by a compound known as SIRT1 in mouse embryonic stem cells. Although SIRT1 has been previously shown to be critical for normal embryonic development, the governing mechanism has been completely unknown.
The scientists produced whole-body SIRT1 knockouts and heterozygotes for the study. Two to three-month old SIRT1 heterozygous female mice were bred with age-matched SIRT1 heterozygous male mice. The next day, females were placed in a new cage and fed either normal chow that contained methionine or a methionine-deficient diet. Embryos were collected and analyzed.
The results indicated that SIRT1 works in conjunction with a gene called Myc to co-regulate methionine metabolism through methionine adenosyltransferase 2a. The authors concluded that methionine metabolism is a critical step in SIRT1 maintenance of embryonic stem cells, and, in turn, the developing embryo. Future studies will evaluate the exact functions of SIRT1 throughout different stages of mouse embryogenesis. (GK)
Citation: Tang S, Fang Y, Huang G, Xu X, Padilla-Banks E, Fan W, Xu Q, Sanderson SM, Foley JF, Dowdy S, McBurney MW, Fargo DC, Williams CJ, Locasale JW, Guan Z, Li X. 2017. Methionine metabolism is essential for SIRT1-regulated mouse embryonic stem cell maintenance and embryonic development. EMBO J 36(21):3175−3193.
Enhancers within genes dampen protein production
NIEHS researchers and their colleagues reported that the presence of an intragenic enhancer, or an enhancer region located inside of a gene, can reduce host gene transcription, which means less production of the encoded protein. Enhancers are small regions of DNA known to help activate gene transcription.
Using CRISPR/Cas9 deletions of the enhancer, a method that allows removal of a specific gene sequence, the researchers saw that intragenic enhancers can also affect how a cell differentiates. Scientists previously thought that enhancers mainly served as activators of transcription, but this research showed that the location of the enhancer is important in determining whether it promotes or slows transcription.
The underlying mechanism is likely interference from RNA polymerase II, which is involved in transcribing the enhancer. The interference might be protective in cases in which the host gene codes for an oncoprotein, because loss of enhancer transcription means loss of interference and gain of host gene expression, leading to the initiation of cancer. These findings uncover an important mechanism that alters protein production, and furthers understanding of the many fine-tuning, regulatory techniques that the cell possesses. (AR)
Citation: Cinghu S, Yang P, Kosak JP, Conway AE, Kumar D, Oldfield AJ, Adelman K, Jothi R. 2017. Intragenic enhancers attenuate host gene expression. Mol Cell 68(1):104−117.e6. (Story)
Rif1 is a novel regulator of ERVs
NIEHS scientists and their collaborators have uncovered novel regulators of endogenous retroviruses (ERVs). The discovery is important, because it provides insights for the proper control of retrotransposons in the mammalian genome.
Retrotransposons are mobile genetic elements that jump around the genome and spread by copying and pasting themselves. ERVs are long terminal repeat (LTR)-retrotransposons, and they can increase the complexity of the genome and regulate the activity of genes in development and disease. If ERVs are not kept under control, they can lead to genome instability and unwanted expression of genes. For this reason, cells have developed mechanisms to inhibit or limit the activity of ERVs.
Researchers performed a test called an RNAi screen to identify factors that are involved in regulating ERVs. They found a list of novel regulators, including Rif1. They further showed that Rif1 directly occupies genomic loci near ERVs. It silences ERVs and nearby genes by promoting the recruitment of epigenetic regulators to maintain a repressive chromatin state. (SS)
Citation: Li P, Wang L, Bennett BD, Wang J, Li J, Qin Y, Takaku M, Wade PA, Wong J, Hu G. 2017. Rif1 promotes a repressive chromatin state to safeguard against endogenous retrovirus activation. Nucleic Acids Res; doi: 10.1093/nar/gkx884 [Online 11 October 2017].
Biomarkers of ovarian reserve do not predict fertility
Donna Baird, Ph.D., an NIEHS epidemiologist, collaborated with fertility specialist, Anne Steiner, M.D., at the University of North Carolina at Chapel Hill, to examine fertility in older women. Surprisingly, they found that biomarkers of low ovarian reserve, which refer to the number of eggs a woman has left, did not predict fertility. The discovery changed the current understanding of fertility.
The study, called “Time-to-Conceive,” followed 750 women who had been trying to conceive for three months or less. Participants provided urine and blood samples at enrollment, then were given home urine pregnancy tests, along with instructions on how and when to test. Blood samples were analyzed for indicators of low ovarian reserve, such as follicle-stimulating hormone (FSH), anti-Mullerian hormone, and inhibin B.
After following participants for 12 months or to the time of conception, the team discovered that indicators of low ovarian reserve were not associated with reduced fertility compared with signs of normal ovarian reserve. The findings may give hope to women with signs of low ovarian reserve who wish to conceive. They also suggested that the commercial fertility tests based on urinary FSH may be of little value for most women. (EM)
Citation: Steiner AZ, Pritchard D, Stanczyk FZ, Kesner JS, Meadows JW, Herring AH, Baird DD. 2017. Association between biomarkers of ovarian reserve and infertility among older women of reproductive age. JAMA 318(14):1367−1376. (Story)
(Gabriel Knudsen, Ph.D., is a Cancer Research Training Award fellow in the National Cancer Institute, Center for Cancer Research, Laboratory of Toxicology and Toxicokinetics. Emilie Mathura is an Intramural Research Training Award (IRTA) postbaccalaureate fellow in the NIEHS Receptor Biology Group. Alicia Richards is a pregraduate fellow in the National Cancer Institute Laboratory of Toxicology and Toxicokinetics. Payel Sil, Ph.D., is an IRTA fellow in the NIEHS Inflammation and Autoimmunity Group. Salahuddin Syed, Ph.D., is an IRTA fellow in the NIEHS DNA Replication Fidelity Group.)