meiosis – BioQuakes

The epigenome is a lesser known part of the study of genetics. It consists of the parts of the genome which are not part of the DNA, for example transcription factors and the accessibility of different sections of the chromatin. DNA in the cell is wrapped around proteins called histones. The wrapping of DNA around these histones are also a factor which controls which parts of the DNA are read into proteins. Furthermore, DNA methylation is an important regulatory factor. The addition of methane groups to DNA makes it impossible to read, effectively shutting off the gene that is methylating.

The epigenome is unique because it can be changed significantly in response to external stimuli. In a way, it is the body’s way of altering DNA on the fly, without actually altering the genetic code. The epigenome can also plays a role in cell differentiation. In class, we discussed how all cells have identical genetic code, passed down from one cell to another. All cells start the same and eventually change into all the different types. The epigenome helps to control exactly which parts of the genome are expressed. It is the epigenome which controls which parts of the genetic code are expressed.

However, the epigenome is still passed down hereditarily and down cell lines. As cells divide through mitosis or meiosis, the epigenome is passed down to the daughter cells. This combination of constant adaptation and persistence through generations make the epigenome an essential part of the body’s function. The combo also makes the epigenome a key part of how the body can be changed for a significant period of time by negative stimuli. These effects can even span generations and have been shown to effect the course of evolution.

Recently, scientists at the University of Liverpool have demonstrated exposure to pollution in water fleas has effects that last over 15 generations. When exposed to a pollutant for a period of 7 months, which encompasses 15 generations of fleas, scientists observed increased rates of DNA methylation. When transferred back to clean water, the scientists found that DNA methylation remained the same. Thus, the pollution permanently damaged the epigenome of the fleas.

Scientists around the world have been using CRISPR/Cas9 in a variety of plant and animal species to edit genetic information. Although this has been tested recently on insects, it is currently moving towards testing mammals. It happens to be more difficult with mammals due to the longevity between generations. However, It’s been done!!

UC San Diego researchers have developed a new active genetic technology in mice. Graduate student Hannah Grunwald, Assistant Researcher Valentino Gantz and colleagues led by Assistant Professor Kimberly Cooper, layed the groundwork for further advances based on this technology, including biomedical research on human disease.

“To demonstrate feasibility in mice, the researchers engineered an active genetic “CopyCat” DNA element into the Tyrosinase gene that controls fur color. When the CopyCat element disrupts both copies of the gene in a mouse, fur that would have been black is instead white, an obvious readout of the success of their approach. The CopyCat element also was designed so that it cannot spread through a population on its own, in contrast with CRISPR/Cas9 “gene drive” systems in insects that were built on a similar underlying molecular mechanism.”

The project duration was two years, and the researchers used many ways to “determine that the CopyCat element could be copied from one chromosome to the other to repair a break in the DNA targeted by CRISPR”. Some gene that was originally existent on only one of the two chromosomes was copied to the other chromosome. They were able to convert one genotype from heterozygous to homozygous, and they were able to tell in that there were as many as 86 percent of offspring that inherited the CopyCat element from the female parent instead of the usual 50 percent.

The test was successful for the female mice’s production of eggs, but not for the males production of sperm. The researchers predict this is a possibility to a difference in the timing of male and female meiosis.

As this test was only the beginning, researchers such as those at UC San Diego hope to soon move on to research on human disease. They say that “Future animal models may be possible of complex human genetic diseases, like arthritis and cancer, which are not currently possible.”, and with their hard work, their research can lead to miracles.

BioQuakes

AP Biology class blog for discussing current research in Biology

Tag: meiosis

The epigenome can be effected by pollution

CRISPR used to Control Genetic Inheritance in Mice!

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