Context : Precise measurements of surface abundances of extremely low metallicity stars have recently been obtained and provide new constraints for the stellar evolution models .

Aims : Compute stellar evolution models in order to explain the surface abundances observed , in particular of nitrogen .

Methods : Two series of models were computed .
The first series consists of 20 M _ { \odot } models with varying initial metallicity ( Z = 0.02 down to Z = 10 ^ { -8 } ) and rotation ( \upsilon _ { ini } = 0 - 600 km s ^ { -1 } ) .
The second one consists of models with an initial metallicity of Z = 10 ^ { -8 } , masses between 9 and 85 M _ { \odot } and fast initial rotation velocities ( \upsilon _ { ini } = 600 - 800 km s ^ { -1 } ) .

Results : The most interesting models are the models with Z = 10 ^ { -8 } ( [ Fe/H ] \sim - 6.6 ) .
In the course of helium burning , carbon and oxygen are mixed into the hydrogen burning shell .
This boosts the importance of the shell and causes a reduction of the CO core mass .
Later in the evolution , the hydrogen shell deepens and produces large amount of primary nitrogen .
For the most massive models ( M \gtrsim 60 M _ { \odot } ) , significant mass loss occurs during the red supergiant stage .
This mass loss is due to the surface enrichment in CNO elements via rotational and convective mixing .
The 85 M _ { \odot } model ends up as a WO type wolf-Rayet star .
Therefore the models predict SNe of type Ic and possibly long and soft GRBs at very low metallicities .

The rotating 20 M _ { \odot } models can best reproduce the observed CNO abundances at the surface of extremely metal poor ( EMP ) stars and the metallicity trends when their angular momentum content is the same as at solar metallicity ( and therefore have an increasing surface velocity with decreasing metallicity ) .
The wind of the massive star models can also reproduce the CNO abundances of the most metal-poor carbon–rich star known to date , HE1327-2326 .

Conclusions :