The activity and expression of matrix metalloproteinase-9/gelatinase B
(MMP-9), an enzyme implicated in the implantation process in mice, was
investigated in normal and parthenogenetic blastocyst outgrowths. Con
ditioned media from parthenogenetic blastocysts after 4 days of cultur
e had reduced levels of MMP-9 activity compared to conditioned medium
from normal outgrowths, levels of MMP-9 mRNA assayed by reverse transc
ription-polymerase chain reaction methods were also reduced in parthen
ogenetic blastocysts compared io normal outgrowths. Geneiic mapping st
udies showed that Mmp9 maps to the distal end of chromosome 2 near the
proxima boundary of a region affected by genomic imprinting. Both par
ental alleles of Mmp9, however, are expressed in 11.5-day embryos deri
ved from interspecific crosses of Mus musculus and Mus spretus. Thus,
loss of MMP-9 activity in parthenogenetic blastocysts does not appear
to be due to imprinting but, rather, due io a defect of trophoblast gi
ant cell proliferation and differentiation. (C) 1997 Wiley-iiss, Inc.