Augustin,
c-kit is a cytoplasmic transmembrane receptor for Stem cell factor and
functions as a tyrosine kinase signalling molecule and is expressed in mast
cells, melanocytes, hematopoietic progenitor cells, and interstitial cells
of Cajal (GI pacemaker cells, so-called) in the myenteric plexus of the
alimentary tract, among other cell types. I don't believe it has anything to
do with marking cells that are in mitosis.

In formalin fixed paraffin embeddied tissues, I would use a Ki-67 antibody
like MIB-1  for demostration of cells that are cycling. The stain has a
nuclear localization and stains cells only in the active part of the cell
cycle.  The monoclonal antibody (MAb) Ki-67 detects a nuclear
proliferation-associated antigen which corresponds to a non-histone protein
with a molecular weight of 395 and 345 kD.

PCNA is a 36 kD nuclear protein associated with the cell cycle. PCNA
(proliferating cell nulcear antigen) was used before Ki 67 but has been
largely supplanted by Ki 67 (MIB-1) since it is less specific, PCNA staining
cells in the resting parts of the cell cycle while Ki 67 more closely
correlates with BRDU studies. PCNA has a longer half-life than Ki 67 and
thus persists in cells that are already in the resting G-phase of the cell
cycle. For technical tips- See reference below wherein investigators stain
bovine stomach with MIB-1 (Ki 67). Hope this helps.

Jeff Silverman HT HTL QIHC (ASCP)
Pathologist's Assistant
Soutside Hospital
Bay Shore NY USA

Reference:

Anat Histol Embryol 2001 Jun;30(3):169-73
Proliferation in the gastric epithelium of bovine abomasum during foetal
development as revealed by Ki-67 immunocytochemistry.
Sommer U, Kressin M.
Department of Veterinary Anatomy, Histology and Embryology, University of
Giessen, Frankfurter Strasse 98, D-35392 Giessen, Germany.
For the first time, proliferative cells in the abomasal mucosa of 30 bovine
foetuses with a crown-rump length of 34 to 1000 mm (approximately 45-250
days of gestation) were detected using the antibody MIB-1 against the
(human) nuclear-associated protein Ki-67. At the beginning of mucosal
development, the epithelium is stratified and MIB-1 positive cells are
scattered all over the epithelium. With the formation of gastric pit/gland
invaginations, the proliferative cells are mostly confined to the basal half
or third of the gastric pit/gland unit, both in the regio glandulae propriae
and in the regio glandulae pyloricae. From the 27th week in the regio
glandulae propriae and the 30th week in the pyloric gland region,
respectively, the proliferative cells move upwards and are situated in the
bottom of the pit and the upper part of the gland, whereas the base of the
gland is free of labelling.