Integrity of hereditary material—the genome —is critical for species survival. Genomes need protection from agents that can cause mutations affecting DNA coding, regulatory functions, and duplication during cell division. DNA sequences called transposons, or jumping genes (discovered by Carnegie’s Barbara McClintock,) can multiply and randomly jump around the genome and cause mutations. About half of the sequence of the human and mouse genomes is derived from these mobile elements.  RNA interference (RNAi, codiscovered by Carnegie’s Andy Fire) and related processes are central to transposon control, particularly in egg and sperm precursor cells.  

The Bortvin lab, with colleagues, identified a key protein that suppresses jumping genes in mouse sperm and found that the protein is vital to sperm formation. It had been known previously that a similar element did this in the fruit fly. The protein, called Maelstrom, is old evolutionarily and found in many organisms. It is implicated in transposon silencing in flies and mice by means of specialized small RNAs known as Piwi-interacting RNAs (or piRNAs).  

Bortvin’s group showed the critical role of transposon silencing for normal fertility of male mice. But only recently did they discover the impact of transposons on the mammalian egg precursor.  The group found that mouse oocytes repress transposons inefficiently. Because of this poor transposon silencing, every oocyte stores this potent mutagen. Safia Malki in the lab correlated transposon abundance with oocyte viability and oocyte cell division reliability. She found that a burst of activity of a single transposon in transgenic mice increased oocyte death. Most strikingly, Malki improved oocyte viability and prevented errors in chromosome segregation by blocking the ability of the transposon to copy itself using a drug that blocks multiplication of HIV, the AIDS-causing virus.

 

This unique mode of transposon control in mouse oocytes sheds light on two puzzles—prenatal death of most oocytes and the age-related increase in chromosome errors, such as those that cause Down syndrome. Malki and Bortvin speculate that the lax control of transposons in mice, and perhaps human oocytes, causes the elimination of oocytes with either highly active transposons or those incapable of more stringent transposon control.

The surviving oocytes may prevent excessive transposon alterations to the genomes and be better suited to support the healthy development of the next generation. The Malki and Bortvin findings also suggest that an ovary of a newborn girl already contains “good” oocytes as well as those predisposed for chromosomal errors. It may be the case that “good” oocytes are ovulated during first two decades of a female’s reproductive life, while “bad” ones are ovulated later.

Bortvin received his Ph. D. in genetics from Harvard and was a postdoctoral fellow at the Whitehead Institute before joining the Carnegie staff in 2004. For more information see Bortvin lab

 

Explore Carnegie Science

This image captures the bright blue light (chemiluminesc ence) emitted by the NanoLuc protein in LipoGlo zebrafish. It is is provided courtesy of James Thierer.
July 31, 2019

Baltimore, MD—A newly developed technique that shows artery clogging fat-and-protein complexes in live fish gave investigators from Carnegie, Johns Hopkins University, and the Mayo Clinic a glimpse of how to study heart disease in action. Their research, which is currently being used to find new drugs to fight cardiovascular disease, is now published in Nature Communications.

Fat molecules, also called lipids, such as cholesterol and triglycerides are shuttled around the circulatory system by a protein called Apolipoprotein-B, or ApoB for short. These complexes of lipid and protein are called lipoproteins but may be more commonly known as “bad cholesterol.”

One analogy for understanding the mathematical structure of the team's work is to think of it as foam being simplified into a single bubble by progressively merging adjacent bubbles.
July 2, 2019

Baltimore, MD—How do the communities of microbes living in our gastrointestinal systems affect our health? Carnegie’s Will Ludington was part of a team that helped answer this question.

For nearly a century, evolutionary biologists have probed how genes encode an individual’s chances for success—or fitness—in a specific environment.

In order to reveal a potential evolutionary trajectory biologists measure the interactions between genes to see which combinations are most fit.  An organism that is evolving should take the most fit path. This concept is called a fitness landscape, and various mathematical techniques have been developed to

June 17, 2019

Meredith Wilson, a postdoctoral associate in Steve Farber’s lab at the Department of Embryology, has been awarded Carnegie’s thirteenth Postdoctoral Innovation and Excellence Award. These prizes are given to postdocs for their exceptionally creative approaches to science, strong mentoring, and contributing to the sense of campus community. The nominations are made by the departments and are chosen by the Office of the President. The recipients receive a cash prize and are celebrated at an event at their departments.  

Wilson came to Carnegie in 2014 from the University of Pennsylvania with a background in cell biology investigating how motor proteins position

Illustration of a thymus in a human chest courtesy of Navid Marvi.
May 29, 2019

Washington, DC—Aging-related inflammation can drive the decline of a critical structural protein called lamin-B1, which contributes to diminished immune function in the thymus, according to research from Carnegie’s Sibiao Yue, Xiaobin Zheng, and Yixian Zheng published in Aging Cell.

Each of our cells is undergirded by a protein-based cellular skeleton. And each of our tissues is likewise supported by a protein matrix holding the cells that comprise it together. These protein scaffolds or structures are necessary for organs and tissues to be constructed during development.

“Since organ building and maintenance require this protein-based structural support

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The Zheng lab studies cell division including the study of stem cells, genome organization, and lineage specification. They study the mechanism of genome organization in development, homeostasis—metabolic balance-- and aging; and the influence of cell morphogenesis, or cell shape and steructure,  on cell fate decisions. They use a wide range of tools and systems, including genetics in model organisms, cell culture, biochemistry, proteomics, and genomics.

 

The Spradling laboratory studies the biology of reproduction. By unknown means eggs reset the normally irreversible processes of differentiation and aging. The fruit fly Drosophila provides a favorable multicellular system for molecular genetic studies. The lab focuses on several aspects of egg development, called oogenesis, which promises to provide insight into the rejuvenation of the nucleus and surrounding cytoplasm. By studying ovarian stem cells, they are learning how cells maintain an undifferentiated state and how cell production is regulated by microenvironments known as niches. They are  also re-investigating the role of steroid and prostaglandin hormones in controlling

The Marnie Halpern laboratory studies how left-right differences arise in the developing brain and discovers the genes that control this asymmetry. Using the tiny zebrafish, Danio rerio, they explores how regional specializations occur within the neural tube, the embryonic tissue that develops into the brain and spinal cord.

The zebrafish is ideal for these studies because its basic body plan is set within 24 hours of fertilization. By day five, young larvae are able to feed and swim, and within three months they are ready to reproduce. They are also prolific breeders. Most importantly the embryos are transparent, allowing scientists to watch the nervous system develop and to

The Gall laboratory studies all aspects of the cell nucleus, particularly the structure of chromosomes, the transcription and processing of RNA, and the role of bodies inside the cell nucleus, especially the Cajal body (CB) and the histone locus body (HLB).

Much of the work makes use of the giant oocyte of amphibians and the equally giant nucleus or germinal vesicle (GV) found in it. He is particularly  interested in how the structure of the nucleus is related to the synthesis and processing of RNA—specifically, what changes occur in the chromosomes and other nuclear components when RNA is synthesized, processed, and transported to the cytoplasm.

Staff Associate Kamena Kostova joined the Department of Embryology in November 2018. She studies ribosomes, the factory-like structures inside cells that produce proteins. Scientists have known about ribosome structure, function, and biogenesis for some time. But, a major unanswered question is how cells monitor the integrity of the ribosome itself. Problems with ribosomes have been associated with diseases including neurodegeneration and cancer. The Kostova lab investigates the fundamental question of how cells respond when their ribosomes break down using mass spectrometry, functional genomics methods, and CRISPR genome editing.

Kostova received a B.S. in Biology from the

Sally June Tracy applies cutting-edge experimental and analytical techniques to understand the fundamental physical behavior of materials at extreme conditions. She uses dynamic compression techniques with high-flux X-ray sources to probe the structural changes and phase transitions in materials at conditions that mimic impacts and the interiors of terrestrial and exoplanets. She is also an expert in nuclear resonant scattering and synchrotron X-ray diffraction. She uses these techniques to understand novel behavior at the electronic level.  Tracy received her Ph.D. from the California Institute of

The Ludington lab investigates complex ecological dynamics from microbial community interactions using the fruit fly  Drosophila melanogaster. The fruit fly gut carries numerous microbial species, which can be cultured in the lab. The goal is to understand the gut ecology and how it relates to host health, among other questions, by taking advantage of the fast time-scale and ease of studying the fruit fly in controlled experiments. 

Nick Konidaris is a staff scientist at the Carnegie Observatories and Instrument Lead for the SDSS-V Local Volume Mapper (LVM). He works on a broad range of new optical instrumentation projects in astronomy and remote sensing. Nick's projects range from experimental to large workhorse facilities. On the experimental side, he recently began working on a new development platform for the 40-inch Swope telescope at Carnegie's Las Campanas Observatory that will be used to explore and understand the explosive universe.

 Nick and his colleagues at the Department of Global Ecology are leveraging the work on Swope to develop a new airborne spectrograph that will be