Cloning is a difficult process. Even with modern technologies, the best we can do is generate matching organs from a person’s stem cells, but this itself is still tricky to accomplish. Actually cloning a whole organism? We’re nowhere near where we need to be.
The Troubles of Cloning
The main problem inherent in this process is the same one that comes from attempts to use artificial wombs for embryonic development. The first required step is to be able to generate an embryo properly. And knowledge on early embryonic development for mammals in general is fairly sparing. It is just too difficult to replicate or study directly.
Luckily, at least on the topic of cloning, significant progress has been made on reverting cells back into stem cell forms. More work remains to be done, but the field has advanced tremendously over the past few decades.
Similarly, another accomplishment published in the journal Science may have ramifications for organ development, embryonic research, and cloning as a whole.
Researchers at the University of Cambridge have been able to combine two forms of stem cells to create an artificial embryo in mice that seems to directly replicate embryo production within living creatures.
How Do Embryos Work?
To understand how they did this, first some background on how embryos develop is needed. Once fertilization has occurred, the fertilized egg undergoes rapid cellular division from one to many cells. After about 5 days, this mass of cells has together created what is called a blastocyst.
This multi-layered cellular structure has multiple parts that make it up. The trophoblast is the outer layer of cells that acts as a cell wall and has a number of additional functions related to hormonal secretions and the formation of several particular body functions from these stem cells, such as the placenta.
It also is responsible for managing implantation of the blastocyst into the uterine cell wall, which occurs not long after. The type of stem cells that make up the trophoblast are known as extra-embryonic trophoblast stem cells (TSCs), which are important for a later discussion.
The internal cavity of the blastocyst is appropriately called the blastocoel. But the blastocyst isn’t just an empty shell, there is another structure inside of it. This is called the embryoblast, made up of embryonic stem cells (ESCs) that form the vast majority of the resulting body. These form near one end of the blastocyst where it will implant into the uterine wall.
The final group of cells are the primitive endoderm stem cells that form the amniotic sac around the embryo and fill up the rest of the uterus.
All of these forms of cells work together to create and establish the embryo from the initial fertilized egg. Because of this, you can see why experiments using only ESCs (under the thought of them being the primary formation structures for almost all the cells in the body) in order to replicate an embryo were not successful.
That all changes now with the current experiment. In this study, the researchers combined the use of ESCs and TSCs using a “3D-scaffold”, also called an extracellular matrix, to hold the cells together. On this matrix, the two types of cells formed together into a structure directly resembling a blastocyst and a developing embryo.
It should be noted that to accomplish this properly, they used genetically-modified stem cells and certain inhibitors and hormones to replicate the surroundings under which the blastocyst would normally form. Combining these two types of cells artificially created what they termed an ETS-embryo and it is able to replicate the first 13 days of embryonic development.
Unfortunately, this is only preliminary work, as without the third kind of stem cell to form the amniotic sac, the blastocyst lacks the proper nutrients to proceed beyond this 13-day stage.
A Wide Range of Research
Even so, the success of this experiment and the easy creation of early-stage mice embryos allows direct study of this very early period of development and for scientists to test their stem cell formation methods.
A key benefit this sort of research will provide is information on how certain birth defects from early embryo formation first appear and may allow ways of treating them to be discovered.
Future experimentation and more research should reveal ways to further even this technique, leading to the eventual hopeful goal of complete embryonic development.
Photo CCs: 4cell embryo from Wikimedia Commons