New insights into the role of Kit ligand during mouse germ cell development

Kit ligand [KITL, also known as mast cell growth factor (MGF), stem cell factor (SCF), and Steel factor] and its receptor, KIT, are essential for embryonic and postnatal development of both male and female germ cells. While germ cells express KIT at multiple stages in their development, somatic cells that support the growth and differentiation of germ cells express KITL. Numerous studies have revealed that KITL promotes proliferation and suppresses apoptosis of germ cells. However, many details of the molecular mechanisms by which KITL signaling affects proliferation, apoptosis, migration and differentiation of germ cells are not known. Our laboratory recently identified hypomorphic mutations in the Steel locus (KitlSl) that allowed fine dissection of the role of KITL during germ cell development. KitlSl homozygous mutants that were previously analyzed exhibited perinatal lethality or had severe germ cell defects thus limiting the understanding of the role of KITL. Therefore, the newly identified hypomorphic mutations that exert graded mild effects on germ development were able to provide new insights into additional and novel roles of KITL at multiple stages of germ cell development.