The following Division of NTP branches at NIEHS are actively involved in NTP research activities: Biomolecular Screening Branch, led by Raymond Tice, Ph.D. until his retirement in December 2014, and now led by acting chief Rick Paules, Ph.D.; Cellular and Molecular Pathology Branch, led by Robert Sills, D.V.M., Ph.D.; NTP Laboratory, led by acting chief Michael Devito, Ph.D.; Program Operations Branch, led by Michelle Hooth, Ph.D.; and Toxicology Branch, led by Paul Foster, Ph.D.
Genetic and epigenetic differences between individuals in the human population are proposed as major factors for individual susceptibility to environmental stressors. Environmental and drug safety assessments are currently conducted with a small number of commonly used animal models, which have limited genetic diversity. Further, there are many layers of biological regulation that can influence individual genetic susceptibility to chemical and drug toxicity. Animal models have inherent limitations in extrapolating results to human toxicity and disease, and this program is working toward development of more sophisticated analyses in epigenetics to make better use of current animal models, and adopt biological systems that are more appropriate for modeling human toxicity and disease. The NTP Biomolecular Screening Branch conducts in-house projects aimed at understanding individual susceptibility.
In FY 2015, work continued on the mouse methylome project by Alex Merrick, Ph.D., and Paul Wade, Ph.D. Epigenetics involves the study of modifications to DNA, like methylation, and related cellular structures, such as histones, that affect gene expression and an organism’s ability to adapt to the environment. NTP designed an epigenetic study to examine DNA methylation and its possible relationship with the susceptibility of mouse strains to develop liver tumors. Male and female C57BL/6N mice were crossed with C3H/HeN mice. Five tissues — brain, liver, cardiac and skeletal muscle, brown and white fat, and epididymal sperm — from the first generation offspring were collected, at the average age NTP starts mice in a subchronic toxicity study, and flash frozen for DNA/RNA isolation and liver sequencing. Progress in FY 2015 involved computational analysis on sites of genomic methylation in relation to known genes and transcriptionally active regions in both parental strains and the resulting first generation offspring. The relationship of DNA methylation to gene expression and possible heredity in offspring is being determined, and the genomic variation between mouse strains, genders, and F1 offspring is being catalogued. The epigenetic landscape is being carefully described in these two mouse strains and offspring to help interpret the contribution of differences in DNA methylation to their differential susceptibility to hepatic malignancy. A manuscript is in preparation to be followed by public release of the methylome data. Additional studies in 2015 have been initiated that will address the impact of sex hormone signaling on DNA methylation at a genome-wide level, and the impact of DNA methylation at distal regulatory regions.
The NTP Laboratory, within the NIEHS Division of NTP, conducts in-house, agent-specific, targeted research related to the development and application of modern toxicology and molecular biology tools. These tools are used in the evaluation of specific substances of concern to NTP, issues of central importance to NTP programs, and methods development to advance the NTP mission. The NTP Laboratory also focuses on the study of the developmental origins of adult diseases. The table below includes projects in the NTP Laboratory in FY 2015.