Epigenetic inheritance occurs asymmetrically

The Hopkins chapter of the National Biological Honor Society hosted their Fall 2019 Faculty Speaker lecture on Thursday, Oct. 31. The speaker was Xin Chen, an associate professor in the Department of Biology. 

Her presentation focused on epigenetic inheritance. The study of epigenetics deals with the mechanisms through which cells inherit phenotypic changes without changes in the inherited DNA sequence.

Chen explained that when stem cells divide to produce two daughter cells, these two cells have differing identities. 

“Stem cells that reside in normal tissue inside our body, such as our gut, blood or skin, help replenish the lost cells over time,” she said. “For this, stem cells have to undergo division, which gives rise to cells with different fates. One daughter cell will be an identical stem cell and the other will become the cell type of the tissue in which the stem cell resides.”

Chen mentioned that the team at her laboratory has proposed a two-step model to explain this asymmetric epigenetic inheritance. The first step is the differential distribution of old and new histones, which are groups of proteins found in DNA. 

“On the leading strand we can see a high density of old histones while the lagging strand has a higher density of new histones,” she said.

The second step segregates the sister chromatids containing old histones to the stem cell while the set containing new histones is segregated to the daughter cell which will become a different cell type. Chen revealed that in order to understand how this happened, they examined the behavior of microtubules, which are structures that aid in the separation of chromosomes into the daughter cells during mitosis. 

“The microtubules become active from one side and then later become active on the other side. If we utilize a high resolution microscope, you can appreciate that the microtubule coming from one side is way more active than the microtubule coming from the other side,” she said.

The mechanisms that Chen described intrigued sophomore David Cao.

“I particularly enjoyed being able to learn about and understand the mechanisms through which two cells can have different traits despite having the same genes,” he said in an interview with The News-Letter. 

The findings that Chen presented are of particular significance since epigenetics is viewed as a promising cancer treatment. It is believed that through epigenetic alteration, cancerous cells could be reprogrammed to a normal state. 

Epigenetics is a major field of research at Hopkins, where faculty and post-doctoral fellows at the Center for Epigenetics collaborate to find, among other things, the epigenetic drivers of cancer progression and neuropsychiatric diseases. The Center offers an opportunity for students to learn about the topics they research through a course titled Physical Epigenetics that is taught by faculty from the Center during the spring.

The fact that epigenetic techniques may lead to wide-ranging therapies and treatments was a primary draw for Cao to the lecture.

“The most interesting aspect of epigenetics is that it is reversible and that it has the potential of allowing us to control diseases and habits,” he said. 

During an interview with The News-Letter, sophomore Lina Tewala expressed her belief that the talk helped her to understand some of the applications of concepts she learned in her Biophysics courses. 

“It was interesting to find out that what I am learning about can be applied to other fields of study because an important part of the field of biophysics is the study of proteins and genes,” she said.