Bianca Jones Marlin, PhD, is a neuroscientist—and new mom—who studies the biology of parental behavior. Last year, she was among the first to receive a STAT Wunderkinds award, which recognizes early-career scientists for groundbreaking work. We spoke with Marlin to learn more about her work, and how her own experience has shaped her research.
Q: What is your research on mothering all about?
I’m trying to find out how nature sets you up for motherhood, and how experience—both positive and negative—changes that.
It’s well-known that oxytocin—also known as ‘the love hormone’—is one of the ways that nature prepares women for motherhood. The hormone is released during intimate activities, like breastfeeding and sex. Scientists have established that oxytocin helps establish a bond between parent and child. That bond is reinforced by eye contact and other interactions.
My earlier research was focused on understanding the biology of that process—what pathway does it use to help forge an emotional bond? In mice, I showed that oxytocin stimulates auditory receptors in the brain. So when a mom breastfeeds, the oxytocin that’s released makes her more responsive to a baby’s cry. In experiments with mice, the animals that had high levels of oxytocin tended to care for pups that were placed near them in a cage. Those that had lower levels of oxytocin ignored the pups, or worse.
Now I’m looking at a different aspect of parenting: how the trauma a parent experiences may be passed down to children and grandchildren via transgenerational epigenetics.
Q: We normally think of traits as being passed down from one generation to the next via genes, or through behaviors that are learned from parents. How is transgenerational epigenetics different?
We inherit our genes from parents, so our genome is set. Epigenetics refers to biochemical markers, acquired from experiences or environmental conditions that become attached to our genes and can change the way they are expressed. Identical twins, for example, have the same genes but different experiences and things in their environment may change their gene expression. So while they may have the same gene that regulates metabolism, something in their environment could suppress or enhance the way the gene works.
My colleagues and I are exploring the concept of epigenetic changes in mice that would allow the trauma a parent experiences to be passed down to its offspring.
We’ve seen in our first set of studies that the offspring of mice that fear a specific odor seem to—somehow—inherit that same representation of fear or threat. In these experiments, we first establish a fear memory in adult mice by pairing an odor that smells like almonds with a mild shock. After the memory is set, whenever these mice encounter this odor, they either freeze or run away from it.
The offspring of these mice—which hadn’t previously encountered the almond odor or the shock—also seem to avoid the same odor. These are preliminary data, but they suggest that the offspring inherited some message that makes them wary of the odor.
We’re trying to figure out how this might happen, and rule out the possibility that that the offspring’s behavior isn’t caused by some external cue. One thing we’re looking at is how the cells in the nose change when the fear memory is established. We’ve found that the parents, after they learn to fear the odor, have more cells in their noses that express the receptor needed to ‘read’ the odor.
Now, we’re looking to see if the offspring also have more of these cells, which would suggest there’s some sort of biological explanation. If that’s the case, we will focus next on finding the epigenetic mechanism that leads to this increase in odor receptor cells—that causes the offspring to make more cells that can sense almond odor without ever experiencing it! That is both mysterious and exciting.
Q: Why is this topic so controversial in the scientific community?
Transgenerational epigenetics is controversial because it seems impossible. It’s extremely difficult to determine if a child’s behavior is due to genetic inheritance or stems from a reaction to the parent’s behavior. So if a parent has PTSD, is the child’s behavior attributed to reacting to the parent or to epigenetic changes that the trauma caused in the parent before the child was born? Evidence suggests that when egg meets sperm, all of the methylation—a common epigenetic marker—is scrubbed away, and the genes are ‘reset’ in the embryo. So how can epigenetic changes be passed to offspring?
Our research is looking at another mechanism of epigenetic inheritance that involves small RNA molecules. Others have found that sperm can take up small RNA molecules, and these molecules are maintained after an embryo is formed. Small RNAs appear to regulate metabolism. Studies have shown that pregnant mice given a low-protein diet had pups that were underweight throughout adulthood. But perhaps more surprising is the finding that male mice given low-protein diet had offspring with altered expression of cholesterol genes in the liver.
We are investigating whether small RNAs could be a mechanism for transmitting the behaviors we see in the offspring of a traumatized parent.
Transgenerational epigenetics is controversial because it seems impossible.
Q: How did you become interested in studying parenting?
My upbringing was very unique. My biological parents were also foster parents, so I had both biological and non-biological siblings. Growing up with siblings who have different parents and genetics piqued my interest in human behavior and human interaction. It led me to study how environments change the way people behave and react in society.
My previous work focused on creating familial bonds through social interactions. I’m hoping to find some mechanism for changing epigenetic markers that are associated with negative social behaviors. The goal of this research, ultimately, is to figure out how to improve the outcome of negative parental relationships.
Q: After you had your baby, did you observe a difference in your own response to babies?
Yes. Because I studied parental behavior before I had a child, I was confident that I knew everything about this topic. But having my own baby made me realize there’s much more to learn.
I now have firsthand experience with the biological effects of oxytocin. It definitely changes the way you see another human. My reaction to my baby is outside of my own control. Even when I’m tired, all my attention is directed to her.
Bianca Jones Marlin, PhD, is a postdoctoral research scientist in the lab of Richard Axel, MD, University Professor in the Department of Neuroscience at Columbia University Vagelos College of Physicians and Surgeons, and Codirector of Columbia’s Zuckerman Institute.