Biophysical modeling of liquid-liquid interactions helps scientists understand cell division

Review written by Alexandra Libby (PNI)

Cell division is one of the most important and well-studied biological processes. Organisms generate new cells in order to grow and reproduce (Figure 1); the types of cell division responsible for each of these goals are called mitosis and meiosis, respectively. Like many biological processes, cell division involves a well-timed, complex coordination of proteins and cellular machinery. Disrupted division can lead to a multitude of problems including genetic mutations, cell death, and cancer (Zhivotovsky and Orrenius, 2010). 

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Life: Like Oil and Water? Part II

Part II of our series into the phenomenon of phase separation that is changing how biologists understand cellular biology

Review written by Xinyang (David) Bing (LSI)

“Repression condensates”

“For liquid-liquid phase separation, Princeton is the center of the universe, and my work benefited from collaborations and interactions with Cliff Brangwynne's lab.” 

This is how Dr. Nicholas Treen, from the lab of Mike Levine, described his close working relationship with the neighboring Brangwynne lab. In his latest publication, he and his collaborators set out to describe a novel type of condensate formation in the nucleus involved in gene silencing. 

The first cell divisions of a newly fertilized embryo are arguably the most instrumental events that occur throughout the life of an animal. During early embryonic development, an intricate web of processes must occur coordinately to lay the blueprint for the developing organism. Like a set of dominoes, every gene that is expressed during early developmental processes leads to consequences downstream during later developmental stages. Even slight errors may lead to a malfunctioning embryo and certain death of the animal. Therefore, all animals have their own set of developmental “blueprints” that necessitate massive numbers of genes be expressed in a tightly controlled manner, both in terms of timing and levels. 

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Alteration of gene activity in response to early life stress

Review written by Rebekah Rashford (PNI)

There is much consensus that negative stressful early life experiences impact the development of an individual. Numerous studies in humans have linked childhood adversity (e.g., loss of a caregiver, abuse, natural disaster, etc.) to an increased risk for depression and other psychiatric disorders in adulthood. In other words, the more an individual has experienced negative stressors in childhood, the more likely that individual is to develop depression or anxiety when they experience mild stressors in adulthood. This heightened sensitization and increased risk of mood disorders in humans has a parallel observation in rodents, specifically mice, which are used as model organisms in the discussed study. Principal Investigator Catherine Jensen Peña and colleagues at the Icahn School of Medicine at Mount Sinai were interested in exploring the epigenetic effects of such early life stressors on reward circuitry in the brain. Throughout this work the authors posit, as does much of the early life stress (ELS) field, that there could be epigenetic mechanisms at work leading to the aforementioned risk of mood disorder development. 

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Life: Like oil and water?

“Rediscovery” of a decades-old physics idea reignites the fields of cellular and molecular biology

Review written by Xinyang (David) Bing (LSI)

Lava lamps are fluorescent mixtures of oil and water that are immiscible and, when heated, float around, generating hypnotizing patterns that lull you to sleep. Now, biologists are seriously considering the possibility that the same physics that govern lava lamps may also control almost everything that goes on inside our cells.1 Walk through the halls of MIT and Harvard, Oxford and Cambridge, or of course Princeton, and you would likely hear what everybody is talking about: liquid-liquid phase separation.

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What can amoebae teach us about “loners”?

Review written by Thiago T. Varella (PSY GS) and Gabriel T. Vercelli (PHY ‘20)

Ever since the spread of SARS-Cov-2 imposed quarantines of global reach, people around the world have voiced their frustrations about social isolation. Indeed, Aristotle said back in 4th century BC, “man is by nature a social animal,” highlighting that our unease towards isolation is at least as ancient as the Classical era. However, as seemingly unnatural as social isolation might be for humans, it plays a crucial role in the current attempts to stave off the pandemic. Interestingly, isolation might serve a similar purpose in the natural world! Individuals that do not engage in collective behaviors have been observed in many social species. This behavioral divergence is usually thought of as an error, a failure to perfectly coordinate all individuals in a population; but this isolation could, at least theoretically be premeditated or shaped by natural selection (Barta, 2016). This leads to the question: are these isolated individuals, also called “loners,” a mere consequence of failed synchronization of the group, or could they be a mechanism nature developed to mitigate the risks of collective action?

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Understanding visual navigation

Understanding visual navigation using cue cells

Review written by Sara Camilli (QCB) and Adelaide Minerva (PNI)

As we go about our daily lives, we often do not consciously think about all the real-world landmarks that we use to position ourselves in space. Yet, as we walk to our local coffee shop or go for a jog in the park, our brain is continuously updating its internal representation of our location, which is critical to our ability to navigate the world. However, we also know that humans and a number of animals can update this internal representation of their position in space even in the absence of external cues. This phenomenon, known as path integration, involves interaction between the parietal cortex, medial entorhinal cortex (MEC), and hippocampus regions of the brain. Prior work has shown that grid cells in the MEC have firing fields that are arrayed in a hexagonal lattice, tiling an environment. Further, there is evidence of inputs to the MEC that encode the velocity at which an animal is moving, which can be used to update the animal’s internal representation of its position. Together, these features support a role of the MEC in path integration. 

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