Scientists create embryo without using sperm or egg – 09/06/2023 – Science

Scientists have developed an entity that resembles an early human embryo, without using sperm, eggs or a uterus.

The team at the Weizmann Institute claims that their “embryo model”, made from stem cells, looks like a perfect example of a real 14-day-old embryo.

It even released hormones that tested positive for pregnancy in a lab test.

The ambition of embryonic models is to provide an ethical way of understanding the first moments of our lives.

The first few weeks after a sperm fertilizes an egg is a period of dramatic change — from a collection of indistinct cells to something that eventually becomes recognizable on an ultrasound.

This timing is crucial for the occurrence of many miscarriages and birth defects, yet it is poorly understood.

“It’s a black box and that’s not a cliché — our knowledge is very limited,” says Professor Jacob Hanna of the Weizmann Institute of Science via video call.

INITIAL MATERIAL

Embryo research is legal, ethical and technically complicated. But there is now a rapidly developing field that mimics the natural development of the embryo.

This research, published in the journal Nature, is described by the Israeli team as the first “complete” embryo model that mimics all the key structures that emerge in the early-stage embryo.

“This really is a perfect picture of a 14-day human embryo,” says Hanna, which “has never been done before.”

Instead of sperm and egg, the starting material was immature stem cells that were reprogrammed to gain the potential to become any type of tissue in the body.

Chemicals were then used to stimulate these stem cells to become four types of cells found in the early stages of the human embryo:

• epiblastic cells, which become the embryo (or fetus) proper
• trophoblastic cells, which become the placenta
• hypoblastic cells, which become the supporting yolk sac
• extraembryonic mesoderm cells

A total of 120 of these cells were mixed in a precise ratio – and then the scientists stopped and watched.

About 1% of the mixture started the journey of spontaneously growing into a structure that resembles, but is not identical to, a human embryo.

“I give the cells a lot of credit—you have to bring in the right mix and have the right environment and it all happens,” says Hanna. “It’s an incredible phenomenon.”

The embryo models were able to grow and develop until they were comparable to an embryo 14 days after fertilization. In many countries, this is the legal limit for normal embryo research.

Despite the late night video call, I can hear the passion as Professor Jacob Hanna takes me on a 3D tour of the “exquisite architecture” of the embryo model.

I can see the trophoblast, which would normally become the placenta, surrounding the embryo. And that includes the cavities – called lacunae – that fill with the mother’s blood to transfer nutrients to the baby.

There is a yolk sac, which performs some of the functions of the liver and kidneys, and a bilaminar embryonic disc—one of the main features of this stage of embryonic development.

‘EVERYTHING MAKES SENSE’

The hope is that embryo models can help scientists explain how different types of cells arise, witness the first steps in building the body’s organs, or understand hereditary or genetic diseases.

This study already shows that other parts of the embryo will not form unless the first placental cells can surround it.

There is even talk of improving in vitro fertilization (IVF) success rates, helping to understand why some embryos fail, or using the models to test whether drugs are safe during pregnancy.

Professor Robin Lovell Badge, who researches embryo development at the Francis Crick Institute, says these embryo models “look very good” and appear to be “quite normal”.

“I think it’s good, I think it’s very well done, it all makes sense and I’m quite impressed,” he says.

But the current 99% failure rate would need to be improved, he adds. It would be difficult to understand what was going wrong in miscarriage or infertility if the model fails to form most of the time.

LEGALLY DISTINCT

The work also raises the question whether embryo development could be mimicked after the 14-day stage.

This would not be illegal, at least in the UK, as embryo models are legally distinct from embryos.

“Some will welcome this – but others won’t like it,” says Lovell-Badge.

Alfonso Martinez Arias, professor at the department of experimental and health sciences at Pompeu Fabra University (Spain), says that this is “very important research”.

“The work achieved, for the first time, a faithful construction of the complete structure [de um embrião humano] from stem cells” in the laboratory, “thus opening the door to studies of the events that lead to the formation of the human body plan”, he says.

The researchers point out that it would be unethical, illegal and, in fact, impossible to achieve a pregnancy using these embryo models – building the 120 cells goes beyond the point at which an embryo could successfully implant in the cervix.

This text was originally published here.