Secretory factors

Well, my curiosities on the stem-cell niche, their locations and their interconnecting functions etc are just ignited me to look are there any ‘secretory factors’ play role for this part. Indeed.. significantly there are some ‘secretory factors’ which play important role in the disorders of stem-cell niche.

References: (from top to below)

For picture 1:

Please click here for complete paper from David T. Scadden

For pictures 2, 3 and 4:

Please click here for complete paper from Michael L. Cher, etal

any opinions?