8.      Human follicular dermal papilla/sheath express the genes for both soluble and membrane-bound stem cell factor (SCF), while the matrix expresses, c-kit, its receptor: implications for the control of hair pigmentation. 
Tayyebeh Vafaee, Isobel De Oliveira, Stephen Picksley, Val Randall, Dept. of Biomedical Sciences, University of Bradford, UK

Stem Cell Factor (SCF) or Mast Cell Growth Factor (MGF), Steel factor or c-kit ligand (CL), is a paracrine factor which regulates rodent hair pigmentation. We showed previously that cultured dermal papilla cells secrete SCF and hypothesise the dermal papilla is a local source of SCF regulating human hair pigmentation. SCF exists in both soluble and plasma membrane-bound forms; it binds to plasma membrane receptor, c-kit. This study was designed to determine where c-kit and SCF are found in human hair follicles. Scalp samples, treated with RNAlater to inhibit mRNA degradation, were microdissected to isolate lower follicles; some hair matrixes and dermal papilla/dermal sheaths were isolated separately. Total and poly(A)RNA were isolated, cDNA prepared and reverse transcription-polymerase chain reactions (RT-PCR) undertaken with primers for c-kit and SCF; cDNA quality was checked using â-actin primers. PCR products were separated by gel electrophoresis, checked for size and sequenced. Immunohistochemistry of frozen scalp sections was also performed to localise c-kit and determine whether its expression mirrored melanocyte marker, Mel–5. Lower follicle samples (n=5) produced bands for both forms of SCF and c-kit. Hair matrix samples (n = 6) expressed c-kit and 2 of 3 dermal papilla/sheath extracts expressed both soluble and bound SCF. Sequence analysis showed 100% correlation with known genes. Immunohistochemistry localised c-kit expression to hair bulb cells, co-localising with Mel-5.
Expression of both SCF and c-kit within anagen follicles strongly supports a local paracrine role for this signaling system in human hair pigmentation. The soluble form of SCF detected in whole follicles and the dermal component would correspond to that secreted by cultured dermal papilla cells. C-kit expression by follicles and the matrix components and its co-localisation with melanocyte markers supports a role maintaining melanocyte pigmentation in anagen follicles. The role of the membrane-bound form merits further investigation.