Image of a Platypus, credited to Klaus, under a Creative Commons License (BY-SA 2.0).
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In a groundbreaking study published in 2015, a team of researchers led by Vincent Lynch at the University of Chicago delved into the role of jumping DNA, or transposable elements, in the evolution of mammalian pregnancy. The findings, published in Cell Reports, shed light on how these genetic parasites contributed to the formation of complex gene regulatory networks that are essential for the development of the placenta and successful pregnancy.
According to Lynch's estimation, this process occurred rapidly by evolutionary standards, within a million years. The research team, which included researchers from Stanford University and other institutions, compared the genes that are switched on in the uterus during pregnancy in 13 different animals.
In the ancestor of eutherian mammals, jumping DNA littered the genome with sequences that progesterone can recognize. These sequences allowed progesterone to switch on a vast array of new genes in the uterus during pregnancy, which played a crucial role in the evolution of pregnancy in mammals.
One of the most intriguing findings was the activation of hundreds of genes involved in making eggshell minerals in the uterus of a platypus. This is a unique characteristic that sets platypuses apart from other live-bearing mammals, as they give birth to an egg rather than live young.
The platypus embryo is surrounded by a thin eggshell and nourished by a primitive placenta. The study also revealed that marsupials and eutherians started activating hundreds of genes involved in suppressing the immune system and passing hormonal signals between the mother and foetus.
Lynch's work has significant implications for our understanding of how evolution produces radically new structures, particularly how a limb can begin to develop. His research suggests that large genome-wide changes can reorganize things in larger jumps, implying that radically new structures may evolve in such a manner.
Craig Lowe from Stanford University confirmed that Lynch's work has shown that jumping DNA can indeed perform such functions. However, more research is needed to fully understand the intricate mechanisms involved in this evolutionary process.
For those interested in delving deeper into this fascinating topic, the study by Lynch, Nnamani, Kapusta, Brayer, Plaza, Mazur, Emera, Shehzad, Sheikh, Grutzner, Bauersachs, Graf, Young, Lieb, DeMayo, Feschotte, and Wagner can be found at this link: http://dx.doi.org/10.1016/j.celrep.2014.12.052
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