We discuss the recent data of exclusive $pi^0$ (and $pi^+$) electroproduction on the proton obtained by the CLAS collaboration at Jefferson Lab. It is observed that the cross sections, which have been decomposed in $sigma_T +epsilonsigma_L$, $sigma_{
TT}$ and $sigma_{LT}$ structure functions, are dominated by transverse amplitude contributions. The data can be interpreted in the Generalized Parton Distribution formalism provided that one includes helicity-flip transversity GPDs.
This work reviews the recent developments in the field of Generalized Parton Distributions (GPDs) and Deeply virtual Compton scattering in the valence region, which aim at extracting the quark structure of the nucleon. We discuss the constraints whic
h the present generation of measurements provide on GPDs, and examine several state-of-the-art parametrizations of GPDs. Future directions in this active field are discussed.
