Egg cells start out as round blobs. After fertilization, they begin to transform into humans, dogs, fish, or other animals by directing head to tail, back to abdomen, and left to right. Exact positioning of these bodybuilding guides has been measured but not observed. Now researchers at the marine biological laboratory (MBL) have plotted the very beginning of this cellular remodeling, and their findings help answer a fundamental question .
“The most interesting and mysterious part of developmental biology is the origin of the body axis in animals,” said researcher Tomomi Tani. MBL scientist at the Eugene Bell Center at the time of the research, Tani is now with the Japan National Institute for Industrial Science and Technology.
The work by Tani and Hirokazu Ishii was reported, this week in Cell molecular biology, showing that both parents contribute to their children’s physical guidance. For the animal species studied in the study (sea squirts), insertion from the mother sets the axis of the dorsal abdomen while the father does so for the axis of the tail.
“Both mothers and paternal mothers need to establish the body plan of the developing animal embryo,” Tani said.
This research addresses fundamental issues in developmental biology and may also provide information on why things go wrong. Such knowledge could benefit fields as diverse as medicine and agriculture.
The most common theory as to how the body’s axis is set is that actin filaments inside the egg, which are involved in cell movement and contraction, power cytoplasmic reticulum. in the egg after fertilization. But it has been a challenge because the start of the process takes place quickly and over very small distances within living cells.
To overcome these obstacles, Tani and Ishii used a fluorescence polarization microscope, a technology developed a few years ago at MBL by Tani, Shalin Mehta (now at Chan Zuckerberg Biohub) and MBL Chief Scientist Rudolf Oldenbourg, along with scientists at other institutions. This technology makes it possible to make images of events taking place at distances measured in nanometers, or thousands of times less than the diameter of a human hair. The approach is also very familiar to Tani and others.
“Using polarized light to observe the dynamics of molecular order is a tradition of MBL photography,” noted Tani, one who began pioneering studies with Shinya Inoué in the 1950s. .
When polar, light waves oscillate either partially or completely in one direction: up / down, left / right, clockwise / counterclockwise, and so on. That’s why sieves let polarized light through in one direction, but it stops when turned.
Tani and Ishii attached fluorescent test molecules, which glow when illuminated with the right light, to the actin in eggs of sea squirts (Offense), a marine species that researchers often study as a model for animal development. The probe-actin bond was very rigid, Tani said, allowing the microscope to detect the direction of the actin molecules by working with polarized light.
So, if the actin identified all in one direction, the researchers saw it. If the actin was swayed, they would see these too. When Tani and Ishii looked at infertile eggs, they saw a mostly random actin arrangement. After fertilization, a wave of calcium went through the egg and the actin filaments lined and contracted on the right side, or 90o, angle to back / future belly. The cytoplasm then moved. The process of creating this body plan began immediately after fertilization.
The fertilized egg study is being followed up with other investigations. One of the long-term goals of such images is to locate and understand the force in the developing embryo that shapes its morphology, shape and and structure.
“We hope that the molecular orders in the cytoskeleton tell us something like ‘field lines’ of mechanical forces that shape the morphology of multicellular organisms,” Tani said in talking about future endeavors.
Source:
Marine Biology Laboratory