News – To see how a tiny ball of identical cells on its way to a mammalian embryo first attaches to a waiting uterine wall and then develops into the nervous system , heart, stomach and organs: This has been highly sought after in the field of embryonic development for nearly 100 years. Now, Prof. Jacob Hanna of the Weizmann Institute of Science and his organization have accomplished this task. The method they created for the growth of extraterrestrial mouse embryos at the initial stages after embryo implantation will provide an unprecedented mechanism for understanding the development program coded in the genes, and may provide detailed insights into birth and developmental deficits as well as those involved in embryo implantation. The results were published in Nature.
Professor Hanna, who is in the Institute’s Molecular Genetics Department, explains that much of what is currently known about mammalian endogenous development comes through monitoring the a process in mammals, such as frogs or fish that lay visible eggs, or receive static images. from dissected mouse embryos and combining them. The idea of growing early-stage embryos outside the uterus has been around since the 1930s, Drs. Hanna says, but these tests were not very successful and the embryos tended to be abnormal.
Professor Hanna’s team decided to renew that effort to advance the research in his laboratory, which focuses on the way in which the developmental program is activated in embryonic stem cells. Over seven years, through trial and error, fine tuning and double examination, his team came up with a two-step process in which they were able to grow normally developing mouse embryos outside the uterus for six days – about a third of their 20-day gestation period – around that time the embryos have a clear body plan and visible organs. “For us, that is the most mysterious and exciting part of pioneering development, and we can now look at it and try it out in detail,” said Dr. Hanna.
The research was led by Alejandro Aguilera-Castrejon, Dr. Bernardo Oldak, the late Dr. Rada Massarwa, and Dr. Hanna Novershtern in the laboratory of Professor Hanna and Dr. Itay Maza, who was a student of Professor Hanna now in Rambam Health Technion Care Campus – Israel Institute of Technology.
For the first step, which lasted about two days, the researchers began with mouse embryos for several days – just after they were inserted into the uterus. At this stage, the embryos were balls containing 250 identical gas cells. These were placed on a special growth medium in a laboratory basin, and the team got the balls to attach it to this medium as they would to the uterine wall. With this step, they succeeded in doubling the first stage of initial development, in which the embryo doubles and triples in size as it differs in three layers: internal, central and external.
Over two days, as the embryos entered the next stage of development – the formation of organs from each of the layers – they required additional conditions. For this second step, the scientists placed the primroses in a nutrient solution in tiny bakeries, mounted on rollers that kept the solutions stirring and mixing constantly. That combination apparently helped keep the embryos, which were growing without maternal blood flow to the placenta, immersed in the nutrients. In addition to carefully controlling the nutrition in the bakers, the team learned in further experiments to closely control the gases, oxygen and carbon dioxide – not just the amounts, but the gas pressure as well.
To determine whether the developmental processes they were monitoring ranged across the two normal phases, the team made careful comparisons with embryos removed from pregnant mice in the appropriate time, indicating that both sequential separation and organ formation were exactly identical in both groups. In subsequent experiments, they inserted into the genes embryos that identified the growing organs in fluorescent dyes. The success of this effort suggested that further experiments with this system, including various genetic and other treatments, should provide reliable results. “We believe that you can inject genes or other elements into the cells, alter the conditions or infect the embryo with a virus, and the system we have shown will give you results that are compatible with development within the uterus of a mouse, ”says Dr. Hanna.
“If you give an embryo the right position, its genetic code will act as a line of predetermined dominoes, set to fall one after the other,” says Dr. Hanna says. “Our goal was to recreate these situations, and now we can watch, in real time, as each domino hits the next one along a line.” It states, among other benefits, that the method will reduce cost and speed up the research process in the field of developmental biology and reduce the need for laboratory animals.
Of course, the next step in Professor Hanna’s lab is to determine if they can phase out the removal of embryos from pregnant mice. He and his team plan to try to create artificial embryos made from stem cells for use in this research. Among other things, they hope to implement their new approach to answering such questions as to why so many implants fail, why the window for implantation is so short, how basic cells lose their “stem” as differentiation progresses, and a situation in body movement can lead to developmental disorders.
Also participating in this research were Tom Shani, Shadi Tarazi, Jonathan Bayerl, Valeriya Chugaeva, Dr. Muneef Ayyash, Shahd Ashouokhi, Daoud Sheban, Nir Livnat, Dr. Lior Lasman, Sergey Viukov, and Drs. Mirie Zerbib from the Department of Molecular Genetics; Dr. Yonatan Stelzer, Dr. Yoach Rais, and Dr. Saifeng Cheng from the Department of Molecular Cell Biology; Dr. Yoseph Addadi and Dr. Hadas Keren-Shaul from the Department of Basic Resources Life Sciences – all at the Weizmann Institute of Science; Dr. Nadir Ghanem and Chen Itzkovich of Rambam Medical Center; Dr. Sharon Slomovich from the Technion – Israel Institute of Technology; and Raanan Shlomo of Arad Technologies.
Professor Jacob Hanna ‘s research is supported by the Kekst Family Institute for Medical Genetics; Helen and Martin Kimmel Institute for Stem Cell Research; Dr. Barry Sherman Institute for Therapeutic Chemistry; Pascal and Ilana Mantoux; Biology Implementation Maurice and Vivienne Wohl; Dr. Gas Cell Research Fund Beth Rom-Rymer; Edmond de Rothschild Foundations; Zantker Charitable Foundation; the estate of Zvia Zeroni; the New York Stem Cell Foundation (NYSCF); Flight Attendant Medical Research Institute (FAMRI); European Research Council (ERC) Convention grant; Israeli Research Foundation (ISF); US-Israel Binational Science Foundation (BSF); and the Israel Cancer Research Fund (ICRF).
The Weizmann Institute of Science in Rehovot, Israel, is one of the top multidisciplinary research centers in the world. The Institute’s strong 3,800 scientific community is engaged in research addressing critical problems in medicine and health, energy, technology, agriculture and the environment. Unique young scientists from around the world take advanced degrees at the Feinberg Graduate School at the Weizmann Institute. The discoveries and theories of Weizmann Institute scientists have had a profound impact on the wider scientific community, as well as the quality of life of millions of people around the world.