What is a defining characteristic of totipotent stem cells?

Totipotent stem cells are uniquely characterized by their ability to differentiate into all possible cell types in an organism, including both embryonic and extraembryonic tissues. This means that totipotent cells can develop into any cell type necessary for forming a complete individual, such as all the various cell types that make up the body as well as the cells that form the placenta. This capability makes them distinct from pluripotent stem cells, which can differentiate into almost all, but not all, cell types.

Totipotent cells exist in the earliest stages of embryonic development, typically in the zygote and the first few divisions that follow fertilization. As development progresses, cells begin to specialize, leading to pluripotent and multipotent stem cells, which have more limited differentiating potential.

Your understanding of this concept is crucial in understanding stem cell biology and its implications in fields like developmental biology and regenerative medicine.