[In vitro methods of male germ cell specification and differentiation]

Germ line specification is an early cell fate decision essential for the transmission of totipotency over generations. Two types of germ line stem cells populate the male gonads in mammals. Primordial germ cells (PGCs) are the germ line founders only present during prenatal life. Spermatogonial stem cells (SSCs) appear a few days after birth and divide asymmetrically to give rise to one stem cell and one spermatogonia that initiates differentiation to produce spermatozoa. Germ cell specification and differentiation involve specific environmental stimuli and a sequential order of maturing phases required for gamete function. Spatio-temporal controls similarly dictate the erasure of somatic methylation marks and the subsequent acquisition of sex-specific marks at imprinted genes in gametes. We review here the recent advancements in male germ cell derivation from ES cells and discuss the limits of these in vitro methods in providing a kinetics and a microenvironment suitable for the programming of a proper gametic and parental identity.