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phogenesis, the biochemical signal transduction pathways that regulate tran-
scription of mammary specific genes, and the survival of mammary cells (i.e.,
suppression of apoptosis) are all dependant on cell-matrix interactions within
the tissue
(1-6)
. Thus, the tissue has great potential for deciphering the roles of
specific ECM proteins and their cellular receptors, e.g., integrins, in the con-
trol of many aspects of phenotype.
One significant advantage of studying the mammary gland is that the mam-
mary epithelium from one mouse can be transplanted into the stroma of a syn-
geneic host
(7)
. Transplanted epithelium forms a ductal network within the
mammary stroma, and, if the recipient mice are mated the epithelium develops
lactational alveoli. The host mammary epithelium is poorly developed until
puberty, thus if it is surgically removed prior to transplantation, all the new
transplanted epithelium which populates the stroma will have the genotype of
the donor.
This transplantation strategy is particularly powerful for examining the role
of ECM proteins and their receptors in the mammary glands of transgenic or
knockout animals which would otherwise suffer embryonic mortality. We have
used the technique to analyze the function of
6 integrin using mammary
epithelium from knockout mice
(8
,
9)
. These mice have a severe skin blistering
defect and die at or shortly after parturition. However, by transplanting mam-
mary epithelium from affected animals to syngeneic hosts, it has been possible
to analyze the role of
α
6 integrin in mammary development. Such a technique
is equally applicable to the analysis of ECM function. A further advantage of
transplantation and retransplantation is that it allows considerable expansion
of the epithelial cell population derived from just one mammary rudiment. This
is particularly useful when large numbers of cells are needed for subsequent
analysis (
see
Note 1
).
α
1.2. Summary of the Technique
At birth, the murine mammary gland consists of a small epithelial rudiment
located under the nipple. Development then proceeds very slowly until the
onset of puberty (approximately 3 wk postpartum) when the epithelium grows
rapidly into the subcutaneous fat pad and subsequently populates the entire
available stroma. To enable transplantation, the endogenous mammary rudi-
ment of the host gland is removed at 21 d after birth leaving the fat pad devoid
of epithelium. This is known as a “cleared” fat pad. Mammary tissue from
another syngeneic animal is then transplanted into the cleared fat pad where it
will grow and form a functional glandular epithelium (
see
Note 2
).
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