Reacción a "Reactions: macaque embryo-like structures developed and implanted in utero from stem cells"

The study is a step in the characterisation of embryonic development models based on embryonic stem cells. This work is based on the pioneering studies of Nicolas Rivron, who was the first to construct blastocysts with stem cells. The blastocyst is the first milestone in the development of a mammal and, of course, a human being. Rivron was able to build structures similar to mouse and human blastocysts, which he called 'blastoids'. 

From a structural point of view (genes that express their cells), blastoids are almost identical to their natural counterparts, blastocysts. However, the proof of what they are is functional. What the blastocyst does is to implant itself in the uterus and, once well established, begin the construction of the organism with the process of gastrulation: the generation of the seeds of each tissue and organ as they arrange themselves in space. Until now, there was no evidence that blastoids could successfully implant and initiate embryo development. In the case of humans, for obvious ethical reasons.  

In this paper, a group of Chinese researchers present data from macaque blastoids that appear to implant and, they say, initiate gastrulation in the maternal womb. The data appear to be of good quality, and although the frequency of success is low, the demonstration that these blastoids implant seems certain. Less clear is whether they gastrulate [the process by which the embryo acquires three germ layers]. My impression is that the gastrulation process is flawed. The few embryos that initiate this crucial phase of development collapse soon after the process begins.  

The work is a further step in the characterisation of these embryonic stem cell-based developmental models, and there will be others. Their value will depend on two things: reproducibility and demonstration of their scientific value in providing new knowledge. The latter is, for the moment, a long way off. Macaques and humans are different, even in the way blastocysts implant. I see this work as a proof of concept that will be challenging to reproduce because of the cost of the research - working with primates is neither easy nor affordable - but it is clearly evidence that blastocysts will be, are, a useful tool for studying the early steps of uterine implantation, which affect many aspects of infertility.