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| Sperm and Egg Meet Up: How Males Package Their Genome |
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| SciMed - Genetics & Genome | |||
| TS-Si News Service | |||
| Monday, 22 June 2009 09:00 | |||
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Salt Lake City, UT, USA. Are sperm and eggs coequals in conception? If anything, popular explanations tend to ignore the complexity of both by focusing on oversimplified notions of a sperm's role in genetic sex determination. We have known about the importance of the egg for a long time. The egg is a relatively large and impressive biological factory compared with the tiny sperm. Even so, a new study from Huntsman Cancer Institute (HCI) at the University of Utah demonstrates that a sperm delivers a good deal more than a copy of the father's distinctive genes to the egg. In fact, it contains much more complex genetic material than previously thought. Researchers discovered particular genes packaged in a special way within the sperm that may promote fetal development. The findings appear in the journal Nature. The new findings were obtained in the context of research into infertility, hoping to develop improved diagnostic testing. As is so often the case in such research, the observations and analyses can have wider implications, addressing key questions on how a healthy baby is gestated and the events that lead to developmental disorders.
TS-Si  Genetics And The GenomeNew York, NY, USA. Ninety percent of every mammal's genome is dark matter harboring ancient viral DNA that infected our ancestors from as far back as the age of the dinosaurs.
Scientists have uncovered clues as to how our ge...Worcester, MA, USA. A chromosome layer folds into contiguous yarns that harbor groups of genes and regulatory elements, enabling contact for coordinated development work.
This is a new layer in the complex organization of ch... in vitro fertilization (IVF) and andrology lab led by Doug Carrell – along with their joint graduate student, Sue Hammoud.
Study co-leader Brad Cairns, Ph.D., says "Our findings show that the father plays an active role in packaging his genome to help ensure a healthy baby." Cairns is an investigator with HCI and the Howard Hughes Medical Institute (HHMI), and professor of oncological sciences at the University of Utah. "However, they also raise the possibility that a man's aging, health and lifestyle may alter this packaging and negatively affect fertility and embryo development." During fetal development, certain genes apply information to the tasks of tissue and organ development. The new research shows that in sperm, these genes are wrapped in special packaging materials called modified histones. A fertilized egg is helped to develop properly by these modified histones. Apparently, they are key factors in ensuring genes are activated or repressed at the right level, place and time. Chromosomes are long strands of DNA containing thousands of genes, and their packaging helps determine which genes turn on and off. Histones are the chief protein components of chromatin, the complex combination of DNA, RNA, and protein that makes up chromosomes. Chromatin contains genetic material-instructions to direct cell functions. Chromatin packages DNA into a smaller volume to fit in the cell, to strengthen the DNA to allow mitosis and The histones act as spools for the winding of DNA and play a role in gene regulation. Each human cell has about 1.8 meters of DNA, but wound on the histones it reduces to about 90 millimeters of chromatin. When duplicated and condensed during mitosis, the result is about 120 micrometers of chromosomes. Understanding how these genes are activated or repressed leads to a better understanding of how disorders like birth defects and cancer develop. "Genes have on-and-off switches, and understanding them allows us to target them, leading to possible treatments, cures or prevention strategies," says Cairns. "That's the good news." An implication of this study is that factors such as genetic mutations, age or lifestyle may affect sperm chromosome packaging, leading to infertility. "We are hopeful that this work will soon lead to a clinical diagnostic test that will help couples with infertility problems make better informed decisions regarding their prospects for a healthy child," says Cairns. The Cairns Lab will also test if aspects of a man's lifestyle – such as age, diet or health – affect proper packaging and fertility. Other future work includes unraveling a major mystery: how are decision-making genes packaged in eggs? CitationDistinctive chromatin in human sperm packages genes for embryo development. Saher Sue Hammoud, David A. Nix, Haiying Zhang, Jahnvi Purwar, Douglas T. Carrell and Bradley R. Cairns. Nature Advance publication 14 June 2009. doi: 10.1038/nature08162.
Download PDF Abstract Because nucleosomes are widely replaced by protamine in mature human sperm, the epigenetic contributions of sperm chromatin to embryo development have been considered highly limited. Here we show that the retained nucleosomes are significantly enriched at loci of developmental importance, including imprinted gene clusters, microRNA clusters, HOX gene clusters, and the promoters of stand-alone developmental transcription and signalling factors. Notably, histone modifications localize to particular developmental loci. Dimethylated lysine 4 on histone H3 (H3K4me2) is enriched at certain developmental promoters, whereas large blocks of H3K4me3 localize to a subset of developmental promoters, regions in HOX clusters, certain noncoding RNAs, and generally to paternally expressed imprinted loci, but not paternally repressed loci. Notably, trimethylated H3K27 (H3K27me3) is significantly enriched at developmental promoters that are repressed in early embryos, including many bivalent (H3K4me3/H3K27me3) promoters in embryonic stem cells. Furthermore, developmental promoters are generally DNA hypomethylated in sperm, but acquire methylation during differentiation. Taken together, epigenetic marking in sperm is extensive, and correlated with developmental regulators.
 The TS-Si News Service is a collaborative effort by TS-Si.org editors, contributors, and corresponding institutions. Sources can include the cited individuals and organizations, as well as TS-Si.org staff contributions. Articles and news reports do not necessarily convey official positions of TS-Si, its partners, or affiliates. We welcome your comments. Use the form below to leave a public comment or send private correspondence via the TS-Si Contact Page. We will not divulge any personal details or place you on a mailing list without your permission.TS-Si is dedicated to the acceptance, medical treatment, and legal protection of individuals correcting the misalignment of their brains and their anatomical sex, while supporting their transition into society as hormonally reconstituted and surgically corrected citizens.
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The TS-Si News Service
and the TS-Si Research Service are collaborations of TS-Si officials, staff, contributors, and corresponding institutions. The contents do not necessarily convey official positions of TS-Si or its owners, participants, partners, or affiliates.