  At very low metallicity, the effects of differential rotation have a more
important impact on the evolution of stars than at high metallicity. Rotational
mixing leads to the production of great quantities of helium and of primary
$^{14}$N by massive stars. Rotation induces important mass loss and allows
stars to locally strongly enrich the interstellar medium in CNO elements. Stars
formed from interstellar clouds enriched by the winds of fast rotating massive
stars would present surface abundances similar to those of C-rich extremely
metal-poor stars. C-rich stars can also be formed by mass accretion in a binary
system where the primary would be a fast rotating intermediate mass star in the
early-AGB phase. Fast rotation may also lead to the formation of collapsars
even at very low metallicity and make the most massive stars avoid the pair
instability.
