The G-CSF receptor is a type I membrane protein which belongs to the cytokine receptor superfamily, and is specifically expressed in mature neutrophils and neutrophilic precursors. Binding of G-CSF to G-CSFR induces its dimerization. The dimerized receptor transduces growth and differentiation signals which are mediated by the N-terminal and C-terminal halves of the G-CSFR cytoplasmic region. G-CSF activates JAK family kinases, which cause tyrosine phosphorylation of STAT family transcription factors. STATs then stimulate proliferation, and induce differentiation of neutrophilic precursor cells. Genetic defects in the G-CSFR gene cause severe neutropenia (Kosimann's syndrome).