Mb. Harvey et al., PROTEINASE EXPRESSION IN EARLY MOUSE EMBRYOS IS REGULATED BY LEUKEMIAINHIBITORY FACTOR AND EPIDERMAL GROWTH-FACTOR, Development, 121(4), 1995, pp. 1005-1014
Several proteinases from different multigene families have been implic
ated in the uterine invasion required for establishment of pregnancy i
n some mammals. In this study, the expression of matrix metalloprotein
ase gelatinase B (MMP-9), urokinase-type plasminogen activator (uPA) a
nd their inhibitors was investigated during early mouse embryo develop
ment. Transcripts for tissue inhibitors of metalloproteinases (TIMP-1,
-2,-3) and uPA receptor were detected throughout pre- and peri-implant
ation development whilst MMP-9 and uPA mRNAs were first detected in pe
ri-implantation blastocysts associated with the invasive phase of impl
antation. Through use of in situ hybridization, it was shown that MMP-
9 transcripts were strongly expressed in the network of trophoblast gi
ant cells at the periphery of implanting 7.5 day embryos and TIMP-3 tr
anscripts were strongly expressed in the decidua immediately adjacent
to the implanting embryo. uPA transcripts were preferentially expresse
d in the ectroplacental cone and its derivatives. Because these protei
nases are regulated by growth factors and cytokines in other tissues,
the effect of leukaemia inhibitory factor (LIF) and epidermal growth f
actor (EGF) on their activity was investigated. Both LIF and EGF, like
the proteinases, have been implicated in peri-implantation developmen
t. Blastocysts collected on day 4 of pregnancy were cultured 2 days in
TCM 199 + 10% fetal bovine serum to allow outgrowth followed by 24 ho
ur culture in defined media containing either LIF or EGF. Conditioned
media were assayed for uPA activity by a chromogenic assay and MMP act
ivity by gelatin zymography. Both LIF and EGF stimulated uPA and MMP-9
activity in blastocyst outgrowths after 3 days of culture (day 7). Pr
oteinase activity was assayed again at the 5th to 6th day of culture (
day 9 to 10). EGF was found to have no effect whereas LIF decreased pr
oduction of both proteinases. These results demonstrate that proteinas
e activity in early embryos can be regulated by growth factors and cyt
okines during the implantation process and, in particular, they demons
trate the possible involvement of LIF in establishment of the correct
temporal programme of proteinase expression.