Defining totipotency using criteria of increasing stringency

Totipotency is the ability of a single cell to give rise to all the differentiated cells that build the conceptus, yet how to capture this propertyin vitroremains incompletely understood. Defining totipotency relies upon a variety of assays of variable stringency. Here we describe criteria to define totipotency. We illustrate how distinct criteria of increasing stringency can be used to judge totipotency by evaluating candidate totipotent cell types in the mouse, including early blastomeres and expanded or extended pluripotent stem cells. Our data challenge the notion that expanded or extended pluripotent states harbor increased totipotent potential relative to conventional embryonic stem cells underin vivoconditions.