Joyce Chen ’23
When an embryo develops, its cells undergo numerous rounds of cell division and arrange into a highly organized system of tissues that collectively assemble into organs. While positioning themselves at the midline, cells known as angioblasts are responsible for the formation of blood vessels in major arteries and veins. Simultaneously, somites — structures in the developing embryo that give rise to bone, tendons, and skeletal muscles — change their shape, a process referred to as somitogenesis. Although these two important events happen concurrently and at similar locations, not much is known about whether somitogenesis is a factor that causes angioblast migration. A team led by Dr. Benjamin L. Martin of Stony Brook University aimed to determine the link between these two phenomena.
The team used zebrafish as their model system. They specifically wanted to look into all-trans retinoic acid (RA). RA is secreted by somites undergoing somitogenesis; it prompts the development of various structures such as the skeleton and heart. Taking into account that RA is secreted around the time angioblasts move to the midline, the team hypothesized that RA may be a causative factor for angioblast migration. Consequently, the team used two groups of zebrafish embryos, tg(kdrl:GFP) and aldh1a2, with the aldh1a2 group lacking RA. Both groups were observed over a duration of 3 hours. The team observed that the angioblasts in the tg(kdrl:GFP) embryos migrated towards the midline, while the aldh1a2 angioblasts barely moved in that direction and instead were disorderly. In addition, tg(kdrl:GFP) embryos were later subjected to either dimethyl sulfoxide (DMSO) or RA to observe the effects of RA on migration rate. The angioblasts in RA were noticeably faster than those in DMSO. In additional studies, the team observed whether RA leads to cavity formation at the embryonic midline for the angioblasts to enter. The embryos were treated with DMSO or diethylaminobenzaldehyde (DEAB) and were observed over a time-lapse of 4 hours. Interestingly, the embryos in DMSO showed obvious cavity formation, whereas embryos in DEAB had little to no movement of tissues.
The research of Dr. Martin and his team showcases how RA secretion by somites during somitogenesis creates a cavity in the embryo and signals the angioblasts to migrate towards the midline cavity. This study inspires future research on somitogenesis and tissue reorganization, thus bringing society closer to solving the mystery surrounding embryo development.
 E. Paulissen, et al., Somite morphogenesis is required for axial blood vessel formation. bioRxiv 4, 438831 (2021). doi: 10.1101/2021.04.07.438831
 Image retrieved from: https://cdn.pixabay.com/photo/2016/07/13/11/21/embryo-1514192_1280.png