New Developments for Healthier Pregnancies

No matter where we end up in life, everyone begins at the same place: as a developing embryo. We all transform from cells to the complex organisms that we are today, yet this process contains numerous potential complications for both the parent and child-to-be.

Despite advancements in healthcare, a 2020 study done by the Centers for Disease Control shows the United States has the highest maternal mortality rates compared to similarly developed countries, like New Zealand and Canada. It is clear that more attention needs to be focused on the health of the parent and child.

During pregnancy, the health of the embryo and parent are notoriously hard to monitor. Whether it be fluctuations in developmental milestones, impacted development due to environmental conditions, or inconsistent methods of monitoring parental health between pregnancies, it is clear that concrete methods of evaluating health of parent and child are needed. At UC San Diego, the Wilkinson Lab and the Laurent Lab seek novel methods of monitoring embryonic development and pregnancy complications.

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Destruction In Development

While embryonic development centers the creation of life, one of its most important factors is the exact opposite: destruction. As embryonic cells replicate and differentiate rapidly during development, the cells must eliminate possible mutations before they can harm the embryo. But what mechanisms enable this kind of quality control during development, and what is the scope of their impact? The Wilkinson Lab at UC San Diego focuses on just that.

The first stage of development, the blastocyst stage, is vital to future embryo survival. Blastocysts are fertilized eggs composed of two different kinds of cells: the trophectoderm, outer cells that eventually become the placenta, and the embryoblast, inner cells which eventually become the embryo. As these two cell types develop rapidly, they rely on the cell’s ability to correctly produce a protein from a DNA sequence. Typically, cells produce proteins by first reading and transcribing a section of DNA into a complementary strand of messenger RNA (mRNA), which is read by ribosomes and translated into a protein. However, if the produced mRNA contains errors, so will the protein, leading to a range of disorders or possible non-viability of the embryo. To regulate the quality of proteins produced, cells use a process known as nonsense-mediated RNA destruction (NMD). NMD identifies and degrades incorrect mRNA through a pathway of proteins and regulatory factors, preventing malformed proteins from being produced and potentially harming development.

As an MD/PhD student researcher in the Wilkinson Lab, Dr. Jennifer Chousal explored how malfunctioning NMD pathways impact embryonic development. Using a mouse model, Dr. Chousal and her team created “knockout embryos” by removing UPF2, an integral protein of the NMD pathway, from the cell lines. After culturing these knockout cells and waiting for maturation into blastocysts, Dr. Chousal and her team performed outgrowth assays, which measure proliferation and success of cell lines, to evaluate the development of both the outer trophectoderm and the inner cell mass. The assays revealed that, while the trophectoderm remained unaffected, the inner cell mass was unable to develop. These results indicate that despite a successful implantation of the embryo into the uterus and successful placenta formation, the blastocyst would not develop further, making the embryo non-viable. Dr. Chousal’s team found higher levels of programmed cell death upon further investigation of the knockout embryos. Additionally, they experienced difficulty deriving stem cells, suggesting that tissue development would not have been successful in this embryo as stem cells are required to specialize

Stages of Embryonic Development

As the embryo develops, cells are constantly rearranging to form the framework for a new, complex organism

To gain a better understanding of NMD’s role in embryonic development, Dr. Chousal’s team took a specific look at when NMD is most active. They measured levels of RNA degradation throughout several stages of development in healthy embryos. The embryos were observed from the blastocyst phase to the gastrulation phase, in which cells rearrange in layers to prepare for tissue and limb development. Dr. Chousal’s team found a decrease in mRNA degradation levels following embryonic implantation, but found that these levels increased during differentiation of the gastrulation phase. Known factors of the NMD pathway, such as specific proteins like UPF2, followed this trend with low levels during implantation and higher levels during gastrulation. Embryos with normal NMD pathways had both types and levels of expressed proteins that matched those of known, properlydeveloped embryos. In contrast, the knockout embryos did not reach this phase of development and thus did not have levels of RNA measured.

The work of Dr. Chousal and the Wilkinson Lab makes one point clear: the ability to properly regulate mRNA and its related proteins is essential for proper embryonic development. However, even if an embryo develops properly through these milestones, other factors can impact the viability of a pregnancy that are equally difficult to monitor. The Laurent Lab looks to tackle one of the most daunting: preeclampsia.

The Big Impact Of Microrna

Preeclampsia is a condition affecting about 4% of pregnancies, causing high blood pressure, an increased risk for organ damage during pregnancy in the parent, and an increased risk of seizures after birth. Traditionally, doctors look for indicators of preeclampsia by examining blood pressure, analyzing the amount of protein in the parent’s urine, or looking for a previous history of high blood pressure. However, these external indicators are inconsistent between pregnancies, leaving researchers to question if better signals exist within the body. The Laurent Lab investigates this problem further, looking towards microRNA as a solution.

MicroRNA (miRNA), or small segments of RNA, specifically inhibits gene translation, which prevents the synthesis of certain proteins. miRNAs bind to mRNA through complementary base pairs, thereby preventing the mRNA from being processed by ribosomes. Researchers at the Laurent Lab believe that dysregulation of miRNA could potentially predict preeclampsia.

As an undergraduate researcher, current master’s student Cassandra Wauer examined miRNA from extracellular vesicles in mouse urine samples, searching for miRNA segments that could be linked to preeclampsia. She and her team focused on these vesicles due to the critical role they play in intercellular communication, and chose to sample urine due to its ease and lack of intrusion for the subject. Wauer first prepped the urine samples to prevent breakdown of the sensitive miRNA. Following preparation, she processed the samples, performed a quality check using a bioanalyzer to ensure miRNA viability, and entered the data into a larger database. Specifically, Wauer looked for already-identified RNA sequences associated with preeclampsia, and compared previous data to her experimental results of which mice developed preeclampsia.

The results were inconsistent and did not yield what Wauer and her team were searching for. However, she currently works to change the experiment’s focus in the hopes of yielding clearer results. MicroRNA may be too sensitive to be reliable, but perhaps the same information could be gleaned from mRNA or other small RNA molecules. These more resilient molecules could expedite the experiment, as they would allow Wauer to process more than the original experiment’s mere 16 samples in a day. Despite these setbacks, this work presents a promising opportunity for the health of pregnant people, and fine-tuning the specifics may lead to impactful results.

LONG OVERDUE: WELCOMING NEW IMPROVEMENTS

While birth and its related processes are natural and integral to life, efforts are needed to improve the health of parent and child. From monitoring embryonic development to finding early treatment for devastating conditions like preeclampsia, these predictors could benefit people who are pregnant for the first time with no known risk factors. The work of the Wilkinson and Laurent labs is critical in addressing this issue, suggesting that the key to treating potential complications may be found in everyday cellular processes and molecules, like NMD and miRNA. As labs work to advance reproductive science, there becomes a greater opportunity to ensure successful and healthy delivery for all.