If research doesn’t provide causal evidence for effects, can epigenetics be forced in to explain everything?

This 2015 UK bird study found that older mothers had female children who had fewer offspring than did the rest of the house sparrow population. The finding applied also to older fathers and their male children.

In general, if a study didn’t directly demonstrate cause and effect, it isn’t appropriate to force the use of epigenetics to explain everything. That’s what this study did with epigenetic inheritance.

Did the study:

“Demonstrate that this parental age effect..potentially is epigenetically inherited.”

by analyzing DNA across generations?

No!

The researchers ran some numbers that tested the effect of older foster parents where the model’s only other possible explanation was epigenetic inheritance.

Several other things about this study were off:

  • The researchers used the term “fitness” 28 times as shorthand to mean the number of offspring, but only twice was it explained as “reproductive fitness.” This was potentially misleading in some of the contexts of the term’s other uses. For example, several of the cited references used “fitness” in a different context.
  • The researchers went into a long exposition of telomeres, punctuated by citing 11 references, only to say:

    “However it is unclear how telomere dynamics could affect fitness.”

    The next sentence was:

    “An alternative explanation might be the accumulation of deleterious mutations as individuals age.”

    which was additionally irritating because “alternative” assumed that telomeres presented a factual explanation of the study’s findings in the first place. Was this section an artifact of a struggle with the reviewer?

After forcing epigenetic inheritance as an explanatory factor and potentially misleading readers about reproductive fitness and telomeres, the researchers had little basis to conclude that their research had “important implications.”

http://www.pnas.org/content/112/13/4021.full “Reduced fitness in progeny from old parents in a natural population”

Advertisements

Epigenetic DNA methylation and demethylation with the developing fetus

This extremely dense and informative 2014 UK summary study provided details about genomic imprinting:

“An unusual epigenetic process in that it is heritable and results in autosomal gene expression according to parent of origin.”

Several notes of interest:

  • Figure 3 had a fascinating sketch of how the fetus caused the mother’s hypothalamus to:

    “Determine forward maternal planning by directing/orchestrating maternal physiology and postnatal maternalism to synchronize with the development of the fetus.”

  • Figure 4 followed up with a flowchart of how – with a female fetus – the coexistence of three matrilineal generations in the pregnant female (her, the fetus, and the grandmother’s influence on the developing fetus’ ovarian oocytes) enabled intergenerational forward planning.
  • The study briefly noted the significance of genomic imprinting on male sexual behavior, where, if the processes didn’t proceed normally at this early stage of the male fetus’ development, could result in suboptimal adult behavior that didn’t change with experience.

F4.large

I’ll quote a few other unrelated passages that caught my eye.

“The reproductive success of mammals also places a considerable burden on matrilineal time and energy, with some 95% of mammalian female adult life committed to pregnancy, lactation, and maternal care.

Thus, offspring that receive optimal nourishment and improved maternal care will be predisposed to develop a hypothalamus that is both genetically and epigenetically predisposed to this same type of good mothering.

Thus, the fetus controls its own destiny in times of acute starvation, especially in the last trimester of pregnancy, by short-term sacrifice of its placenta to preserve resources critical for brain development.”

http://www.pnas.org/content/112/22/6834.full “Genomic imprinting, action, and interaction of maternal and fetal genomes”


This post has somehow become a target for spammers, and I’ve disabled comments. Readers can comment on other posts and indicate that they want their comment to apply here, and I’ll re-enable comments.

Epigenetic DNA methylation of the oxytocin receptor gene affected the perception of anger and fear

This 2015 Virginia human study:

“Reveals how epigenetic variability in the endogenous oxytocin system impacts brain systems supporting social cognition and is an important step to better characterize relationships between genes, brain, and behavior.”

The researchers did a lot of things right:

  • They studied a priori selected brain areas, followed by whole brain analyses;
  • Their subjects were carefully selected

    “Because methylation levels have been shown to differ as a function of race, we restricted our sample to Caucasians of European descent”

    but they didn’t restrict subjects to the same gender;

  • They acknowledged as a limitation:

    “A lack of behavioral evidence to reveal how these epigenetic and neural markers impact the overt social phenotype.”


One thing on which I disagree with the researchers is their assessment of what needs to be done next. Their news release stated:

“When imagining the future possibilities and implications this DNA methylation and oxytocin receptor research may have, the investigators think a blood test could be developed in order to predict how an individual may behave in social situations.”

Nice idea, but the next step should be to complete the research. The next step is to develop evidence for how the oxytocin receptor gene became methylated.

The subjects had a wide range of DNA methylation at the studied gene site – from 33% to 72% methylated!

Why?

At the same gene site:

“There was a significant effect of sex such that females have a higher level of methylation than males.”

Why?

Given these significant effects, why was there no research into likely causes?

Aren’t early periods in people’s lives the most likely times when the “Epigenetic modification of the oxytocin receptor gene” that “influences the perception of anger and fear in the human brain” takes place?

Wouldn’t findings from research on the subjects’ histories potentially help other people?

http://www.pnas.org/content/112/11/3308.full “Epigenetic modification of the oxytocin receptor gene influences the perception of anger and fear in the human brain”

Oxytocin blocks alcohol intoxication symptoms

This joint 2015 Australian/German rodent study found that oxytocin bound to the brain receptors that cause loss of motor control with alcohol intoxication, and prevented rats from displaying these symptoms:

“While oxytocin might reduce your level of intoxication, it won’t actually change your blood alcohol level,” Dr Bowen said. “This is because the oxytocin is preventing the alcohol from accessing the sites in the brain that make you intoxicated, it is not causing the alcohol to leave your system any faster.”

Vasopressin didn’t have the same effect.

The level of alcohol used to produce this finding was roughly equivalent to a human drinking a bottle of wine over a few hours. Oxytocin didn’t prevent loss of motor control when the equivalent of a bottle of vodka was administered because the excess ethanol found its way into other brain receptors and put the rats to sleep.

The study showed oxytocin acting in its original functionalities such as water regulation rather than with its evolved social functions as described in How oxytocin and vasopressin were repurposed through evolution to serve social functions.

http://www.pnas.org/content/112/10/3104.full “Oxytocin prevents ethanol actions at δ subunit-containing GABA-A receptors and attenuates ethanol-induced motor impairment in rats”

Differing characteristics of languages shape people’s brains differently

This 2015 Chinese study found that the differing characteristics of the Chinese and English languages shape people’s brains differently:

“Our results revealed that, although speech processing is largely carried out in the common left hemisphere classical language areas (Broca’s and Wernicke’s areas) and anterior temporal cortex, speech comprehension across different language groups depends on how these brain regions interact with each other.”

For an informed discussion of the study and related issues, visit http://languagelog.ldc.upenn.edu/nll/?p=17949 and comments.

We can infer from the Would you deprive your infant in order to be in a researcher’s control group? study that this shaping process begins during womb life.

http://www.pnas.org/content/112/10/2972.full “Cross-language differences in the brain network subserving intelligible speech”

Would you deprive your infant in order to be in a researcher’s control group?

This 2015 Harvard study found that exposing extremely premature babies to sounds of their mothers enlarged their auditory cortex.

The lead researcher stated:

“Our findings do not prove that the brains of these babies are necessarily better, and we cannot conclude that they will end up with no developmental disabilities.

We don’t know the advantages of having a bigger auditory cortex.”

It’s too bad that studies like this one have to take deprived infants and further deprive them for use as a control group. I suppose it’s possible that the control group members’ development could just be shifted, similar to the Maternal depression and antidepressants epigenetically change infant language development study.

However, given the findings of the Our early experiences are maintained and unconsciously influence us for years, if not indefinitely study, it’s also possible that the last trimester of womb life is a critical period for a child’s auditory cortex. If timely development doesn’t take place within the environment provided by the mother, there may not be another period to fully catch up on growth and learning, even given the effects of neural plasticity.

http://www.pnas.org/content/112/10/3152.full “Mother’s voice and heartbeat sounds elicit auditory plasticity in the human brain before full gestation”

If you had a disease, would you agree to treatment where you became a lab rat?

This 2015 Czech research studied individual neurons in an area of the limbic system of Parkinson’s disease patients. The findings corroborated several findings of previous research, such as:

“We confirm the importance of the subthalamic nucleus as a hub within the limbic circuitry involved in both emotional valence and arousal processing as in two functionally and spatially segregated systems.”

This statement summed up the study for me:

“Several factors could affect our results and reduce the inferences that can be drawn with regards to the physiology of emotional processing and the role of the subthalamic nucleus in the limbic circuits.

One such factor is that the study was conducted with Parkinson’s disease patients, who are known to have a widespread central nervous system pathology and to experience problems in emotional processing.”

The current study referenced The amygdala is where we integrate our perception of human facial emotion study, which similarly used the opportunity of patients with electrodes implanted for deep-brain stimulation to study individual neurons in the amygdala. However, a design difference was that the amygdala study had healthy control subjects in addition to patients, which led to fewer potential limitations on their findings.

Also referenced was a summary study entitled Exploring emotions using invasive methods: review of 60 years of human intracranial electrophysiology. Despite excluding studies of decision making, reward processing, learning, mood disorders, and pain experiences, it didn’t demonstrate that 60 years of experiments using implanted electrodes in the brains of people with epilepsy had substantially advanced science, other than confirming what fMRI and animal research had shown.

I’m not sure how I would feel if I had a disease where the physicians treated my symptoms in such a way that I became a lab rat for research that wasn’t groundbreaking. Do people with epilepsy and Parkinson’s disease have treatments available that factually resolve the underlying causes?

http://www.pnas.org/content/112/10/3116.full “Distinct populations of neurons respond to emotional valence and arousal in the human subthalamic nucleus”