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Matrix metalloproteinase-9 maps to the distal end of chromosome 2 in the mouse
K J Leco1, M B Harvey, A Hogan
1Ontario Cancer Institute, Princess Margaret Hospital, Toronto, Canada.
Abstract:
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. Conditioned media from parthenogenetic blastocysts after 4 days of culture had reduced levels of MMP-9 activity compared to conditioned medium from normal outgrowths. Levels of MMP-9 mRNA assayed by reverse transcription-polymerase chain reaction methods were also reduced in parthenogenetic blastocysts compared to normal outgrowths. Genetic mapping studies showed that Mmp9 maps to the distal end of chromosome 2 near the proximal boundary of a region affected by genomic imprinting. Both parental alleles of Mmp9, however, are expressed in 11.5-day embryos derived 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 to a defect of trophoblast giant cell proliferation and differentiation.
Insights
Reduced matrix metalloproteinase-9 (MMP-9) activity in parthenogenetic blastocysts is linked to trophoblast giant cell defects, not genomic imprinting. This impacts early embryonic development and implantation processes.
Area of Science:
- Reproductive Biology
- Developmental Biology
- Genetics
Background:
- Matrix metalloproteinase-9 (MMP-9), also known as gelatinase B, is crucial for mammalian implantation.
- Parthenogenetic blastocysts, lacking paternal genetic contribution, exhibit developmental abnormalities.
- Genomic imprinting, where gene expression depends on parental origin, can influence embryonic development.
Purpose of the Study:
- To investigate the activity and expression of MMP-9 in normal versus parthenogenetic mouse blastocyst outgrowths.
- To determine if reduced MMP-9 levels in parthenogenetic blastocysts are due to genomic imprinting.
Main Methods:
- Culture of normal and parthenogenetic blastocysts.
- Assay of MMP-9 activity in conditioned media.
- Quantification of MMP-9 mRNA using reverse transcription-polymerase chain reaction (RT-PCR).
- Genetic mapping of the Mmp9 gene and analysis of allele expression in interspecific crosses.
Main Results:
- Parthenogenetic blastocyst outgrowths showed significantly reduced MMP-9 activity and mRNA levels compared to normal outgrowths.
- Genetic mapping indicated Mmp9 is located near a region affected by genomic imprinting on chromosome 2.
- Both parental alleles of Mmp9 were expressed in hybrid embryos, suggesting Mmp9 is not imprinted.
Conclusions:
- The diminished MMP-9 activity in parthenogenetic blastocysts is not caused by genomic imprinting.
- The underlying cause appears to be a defect in trophoblast giant cell proliferation and differentiation in parthenogenetic embryos.
- These findings highlight the importance of MMP-9 and proper cell differentiation for successful implantation.