Maintenance of germ line and somatic DNA methylation during mouse development

DNA methylation in mammals is involved in several essential processes including X chromosome inactivation, genomic imprinting, and host defense against mobile genetic elements. How methylation is targeted to specific sequences in the germ line and how specific methylation patterns are maintained during development is not fully understood. Genomic methylation is established in the gamete, decreases dramatically during preimplantation development, and is re-established after implantation of the blastocyst. However, the methylation present at imprinted loci is specifically maintained during preimplantation development. Imprinted genes are located in clusters, and within each gene cluster parent-of-origin specific expression is governed by an imprinting center (IC). The ICs of the maternally imprinted murine Snrpn, Kcnq1, and Igf2r gene clusters coincide with their differentially methylated domains (DMDs). We have shown that specific DMD sequences are required to establish differential methylation at an imprinted locus. Hybrid transgenes were generated using a non-imprinted derivative of the imprinted RSVIgmyc mouse transgene, Ig/myc, and sequences from endogenous imprinted gene DMDs. Addition of specific DMD sequences to the Ig/myc transgene restored its imprinting. Only the tandem repeats found within the Snrpn, Kcnq1, and Igf2r DMDs were capable of establishing maternal-specific transgene methylation. These experiments have also shown that the methylation on imprinted gene DMD sequences is specifically maintained during the early stages of preimplantation development. These results clearly demonstrate the importance of tandem repeats in the process of genomic imprinting. DNA methylation is also critical for silencing intracisternal A particle (IAP) transposition within the genome. It is thought that maintenance of IAP element methylation during preimplantation is critical to repress IAP element transcription and transposition. The methylation of IAP element long terminal repeat (LTR) sequences was analyzed at the blastocyst stage of preimplantation development using the bisulfite genomic sequencing technique. These experiments have shown that methylation is maintained on the majority of IAP elements at the blastocyst stage of preimplantation development. However, the methylation on specific IAP elements is completely lost at this time, including the methylation of single IAP element LTRs

Preimplantation expression of the somatic form of Dnmt1 suggests a role in the inheritance of genomic imprints

BACKGROUND: Identical DNA methylation differences between maternal and paternal alleles in gametes and adults suggest that the inheritance of genomic imprints is strictly due to the embryonic maintenance of DNA methylation. Such maintenance would occur in association with every cycle of DNA replication, including those of preimplantation embryos. RESULTS: The expression of the somatic form of the Dnmt1 cytosine methyltransferase (Dnmt1s) was examined in cleavage-stage preimplantation mouse embryos. Low concentrations of Dnmt1s are found in 1-, 2-, 4-, and 8-cell embryos, as well as in morulae and blastocysts. Dnmt1s is present in the cytoplasm at all stages, and in the nuclei of all stages except the 1-cell, pronuclear-stage embryo. The related oocyte-derived Dnmt1o protein is also present in nuclei of 8-cell embryos, along with embryo-synthesized Dnmt1s. Dnmt1s protein expressed in 1-cell and 2-cell embryos is derived from the oocyte, whereas the embryo synthesizes its own Dnmt1s from the 2-cell stage onward. CONCLUSION: These observations suggest that Dnmt1s provides maintenance methyltransferase activity for the inheritance of methylation imprints in the early mouse embryo. Moreover, the ability of Dnmt1o and Dnmt1s proteins synthesized at the same time to substitute for one another's maintenance function, but the lack of functional interchange between oocyte- and embryo-synthesized Dnmt1 proteins, suggests that the developmental source is the critical determinant of Dnmt1 function during preimplantation development

Deletion of the Virion Host Shut-off Gene Enhances Neuronal-Selective Transgene Expression from an HSV Vector Lacking Functional IE Genes

The ability of herpes simplex virus (HSV) to establish lifelong latency in neurons suggests that HSV-derived vectors hold promise for gene delivery to the nervous system. However, vector toxicity and transgene silencing have created significant barriers to vector applications to the brain. Recently, we described a vector defective for all immediate-early gene expression and deleted for the joint region between the two unique genome segments that proved capable of extended transgene expression in non-neuronal cells. Sustained expression required the proximity of boundary elements from the latency locus. As confirmed here, we have also found that a transgene cassette introduced into the ICP4 locus is highly active in neurons but silent in primary fibroblasts. Remarkably, we observed that removal of the virion host shutoff (vhs) gene further improved transgene expression in neurons without inducing expression of viral genes. In rat hippocampus, the vhs-deleted vector showed robust transgene expression exclusively in neurons for at least 1 month without evidence of toxicity or inflammation. This HSV vector design holds promise for gene delivery to the brain, including durable expression of large or complex transgene cassettes

The Near-Earth Object Surveyor Mission

The Near-Earth Object (NEO) Surveyor mission is a NASA observatory designed to discover and characterize near-Earth asteroids and comets. The mission's primary objective is to find the majority of objects large enough to cause severe regional impact damage ($>$140 m in effective spherical diameter) within its five-year baseline survey. Operating at the Sun-Earth L1 Lagrange point, the mission will survey to within 45 degrees of the Sun in an effort to find the objects in the most Earth-like orbits. The survey cadence is optimized to provide observational arcs long enough to reliably distinguish near-Earth objects from more distant small bodies that cannot pose an impact hazard. Over the course of its survey, NEO Surveyor will discover $\sim$200,000 - 300,000 new NEOs down to sizes as small as $\sim$10 m and thousands of comets, significantly improving our understanding of the probability of an Earth impact over the next century.Comment: accepted to PS

Historicism and constructionism: rival ideas of historical change

Simon ZB. Historicism and constructionism: rival ideas of historical change. History of European Ideas. 2019;45(8):1171-1190.A seemingly unitary appeal to history might evoke today two incompatible operations of historicization that yield contradictory results. This article attempts to understand two co-existing senses of historicity as conflicting ideas of historical change and rival practices of temporal comparison: historicism and constructionism. At their respective births, both claimed to make sense of the world and ourselves as changing over time. Historicism, dominating nineteenth-century Western thought and overseeing the professionalization of historical studies, advocated an understanding of the present condition of the human world as developing out of past conditions. Constructionism, dominating the second half of the twentieth century, understood the present condition as the recent invention of certain ‘historical’ environments, without prior existence. As competing ideas of historical change, they both entail a comparison between past and present conditions of their investigated subjects, but their practices of temporal comparison are irreconcilable and represent two distinct ways of historicization

Shared Role for Differentially Methylated Domains of Imprinted Genes

For most imprinted genes, a difference in expression between the maternal and paternal alleles is associated with a corresponding difference in DNA methylation that is localized to a differentially methylated domain (DMD). Removal of a gene's DMD leads to a loss of imprinting. These observations suggest that DMDs have a determinative role in genomic imprinting. To examine this possibility, we introduced sequences from the DMDs of the imprinted Igf2r, H19, and Snrpn genes into a nonimprinted derivative of the normally imprinted RSVIgmyc transgene, created by excising its own DMD. Hybrid transgenes with sequences from the Igf2r DMD2 were consistently imprinted, with the maternal allele being more methylated than the paternal allele. Only the repeated sequences within DMD2 were required for imprinting these transgenes. Hybrid transgenes containing H19 and Snrpn DMD sequences and ones containing sequences from the long terminal repeat of a murine intracisternal A particle retrotransposon were not imprinted. The Igf2r hybrid transgenes are comprised entirely of mouse genomic DNA and behave as endogenous imprinted genes in inbred wild-type and mutant mouse strains. These types of hybrid transgenes can be used to elucidate the functions of DMD sequences in genomic imprinting

The University Of Central Florida Steam Program: Where Engineering Education And Art Meet

ICubed is a National Science Foundation (NSF) funded project housed at the University of Central Florida aimed at increasing participation in STEM fields through coordination and institutional integration. The University of Central Florida Science, Technology, Engineering, Arts and Mathematics (UCF STEAM) is a component of ICubed. As a part of this program, UCF STEM faculty and undergraduate researchers work collaboratively with faculty and students in the College of Arts and Humanities to create science-inspired art based on the STEM researcher\u27s explanations of scientific concepts and possibilities. Since the program\u27s inception in 2010, over 700 University of Central Florida faculty and students have participated in the STEAM program with a large majority coming from engineering fields. An evaluation of the program over the last six years demonstrates that by encouraging strong post-secondary cross-disciplinary collaborations, the UCF STEAM program has enlightened UCF\u27s undergraduate engineering students in a manner that not only leads to greater recognition of the interdependencies of right-and left-brain directed skills but also has helped to improve learning and communication skills. This paper highlights UCF engineering STEAM activities and lends a discussion to the educational impact of such a program