Environmental factors increase the frequency of metabolic disorders. The mechanisms by which these epiphenotypes are transmitted between the exposed and subsequent generations through the paternal germline remains poorly understood. The nuclei of mammalian sperm are highly condensed, the DNA is mostly covered by protamines with only a few retained nucleosomes, and epigenetic information stored in the form of DNA methylation is quickly erased from paternal chromosomes shortly after fertilization. Experiments carried out in our lab suggest a more complex picture of mouse sperm, suggesting the presence of multiple histone modifications, nucleosomes positioned around transcription start sites and transcription factor binding sites, presence of CTCF, cohesin, condensin, FoxA1, Oct4, Nanog, Mediator and RNAPII phosphorylated in Ser2. We also find thousands of enhancers and super-enhancers in a poised or active epigenetic state based on the presence of both specific histone modifications and transcription factors. This information suggests that mammalian sperm contain a rich and complex palette of epigenetic information that could be altered by environmental factors to paint novel phenotypic outcomes in the next generation. In this application, we propose to carry out experiments to dissect the mechanisms by which epigenetic information is established and altered by the environment during male germline development, how this information is stored in sperm, and how it is transmitted to the somatic cells of adult tissues of the next generation. To accomplish this we will use obese mice who are 4th generation descendants of females exposed to Bisphenol A (BPA) during pregnancy. We will use mass spectrometry to identify a wide range of transcription factors present in sperm, and ChIP-seq to examine differences in the distribution of these transcription factors in the sperm of control versus obese mice. We will then use Chromosome Conformation Capture techniques to examine the consequence of alterations in transcription factor binding on the 3D architecture of mouse sperm. To understand how and when differences in the epigenome of control and obese mice are established, we will examine the effect of BPA treatment on transcription and transcription factor distribution using RNA-seq, ATAC-seq and ChIP-seq in primordial germ cells and spermatogonial stem cells. Similar analyses will be performed in adipocytes of obese mice in order to understand which of these epigenetic alterations are maintained in adult tissues and may be responsible for the observed obese phenotype. Results from this work will give critical insights into the mechanisms by which alterations in the epigenome are established and transmitted between generations.
Environmental factors promote adult-onset disease by altering epigenetic mechanisms of gene expression in the tissues and/or germ line of the affected individual and its progeny. Experiments proposed in this application will explore mechanisms by which epiphenotypes are established in the male germline, maintained in the sperm, and transmitted to differentiated cells of adult tissues in the next generation.
| Gold, Hannah B; Jung, Yoon Hee; Corces, Victor G (2018) Not just heads and tails: The complexity of the sperm epigenome. J Biol Chem 293:13815-13820 |
