Objective—To isolate bovine mammary gland cells
with stem cell characteristics.
Sample Population—Monolayers of bovine mammary
Procedure—Mammary gland cell populations were
separated by use of selected media supplements.
Phenotypic characteristics were examined via light
and transmission electron microscopy. Cellular
expression of casein and connexin 43 was identified
immunohistochemically. A scrape-loading and dye
transfer assay was used to examine the mammary
gland cell populations for homogenous gap junctional
intercellular communication (GJIC).
Results—Subpopulations of mammary gland cells
grown in vitro are classified on the basis of their distinct
morphologic features and ability to communicate via gap
junctions. Ultrastructurally, 2 morphologically distinct cell
types were classified as type I and II cells. Type I cells
were small light undiffertiated cells and large light undifferentiated
cells that were deficient in functional gap
junctions (as is characteristic of stem cells). Type II cells
included large light differentiated cells and terminally differentiated
cells; GJIC was functional in type II cells.
Type II cells had cytoplasmic expression of connexin 43,
whereas, type I cells did not. All cells expressed casein.
Conclusions and Clinical Relevance—Subpopulations
of bovine mammary gland cells with stem
cell characteristics were identified. Phenotypic differences
are observed among type I bovine mammary
gland cells with stem cell characteristics. Gap junctional
intercellular communication may be necessary
for the differentiation of stem cells. Characterization
of bovine mammary gland stem cells and their progeny
may provide a new tool with which to study mammary
gland health. (Am J Vet Res 2003;63:396–403)