Research delves into the origins of pregnancy, pointing to an invasive placenta in the last common ancestor of eutherian mammals
From: University at Buffalo
July 1, 2022 -- The
fossil record tells us about ancient life through the preserved remains of body
parts like bones, teeth and turtle shells. But how to study the history of soft
tissues and organs, which can decay quickly, leaving little evidence behind? In
a new study, scientists use gene expression patterns, called transcriptomics,
to investigate the ancient origins of one organ: the placenta, which is vital
to pregnancy.
In a new study,
scientists use gene expression patterns, called transcriptomics, to investigate
the ancient origins of one organ: the placenta, which is vital to pregnancy.
"In some mammals,
like humans, the placenta is really invasive, so it invades all the way through
the wall of the uterus, into the maternal tissue. In other mammals, the
placenta just touches the wall of the uterus. And then there's everything in
between," says senior author Vincent J. Lynch, PhD, associate professor of
biological sciences in the University at Buffalo College of Arts and Sciences.
"So what kind of
placentas were early placentas?" he says. "We use gene expression
patterns to reconstruct the evolution of the placenta and predict what the
placenta of the last common ancestor of eutherian mammals looked like. Our data
tells us that this placenta was invasive, and that non-invasive placentas
evolved multiple times among mammals. This addresses a 150-year-old mystery:
People have been debating what kind of placenta the first one was since
then."
As Lynch explains, all
living mammals other than marsupials and egg-laying monotremes are eutherians,
which have long pregnancies in which the developing fetus evokes a strong
physiological response in the mother.
The research was
published on June 30 in eLife. Lynch led the study with first
author Katelyn Mika, PhD, University of Chicago postdoctoral scholar in human
genetics and in organismal biology and anatomy. Camilla M. Whittington, PhD,
and Bronwyn M. McAllan, PhD, both at the University of Sydney, are also co-authors.
"Our ability to
ask how the placenta might have functioned at different points during its
evolution by using the gene expression profiles of currently existing animals
to reconstruct the ancestors is a really cool approach and provides us more
information on how changing gene expression can contribute to the evolution of
a new trait," Mika says.
To conduct the
analysis, the team compared the genes active in the uterus of various mammals
during pregnancy. After finding that these gene expression profiles correlated
with the degree of placental invasiveness, the scientists used their data to
predict what ancestral mammalian placentas looked like.
The study included
about 20 species, such as the egg-laying platypus, pouch-bearing marsupials,
and a range of eutherian mammals that give birth to live young.
The small subset is one
limitation of the analysis: The authors write in eLife that research on a
larger number of species is needed to help determine the strength of the
findings.
Nevertheless, the study
makes important contributions in understanding how pregnancy evolved, Lynch
says. The results could also benefit modern medicine.
"Knowing which
genes are active among different species during pregnancy tells us about how
evolution works," he says. "But it also tells us about what makes a
healthy pregnancy, and how things might go wrong. We're finding the genes that
establish the right kind of environment for healthy human pregnancies. If those
genes are not expressed in the right way, that might give rise to
problems."
This study was
supported by grants from the March of Dimes and the Burroughs Wellcome Fund
Preterm Birth Initiative.
https://www.sciencedaily.com/releases/2022/07/220701163259.htm
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