Mice that are homozygous null for the Mmp9 (matrix metalloproteinase 9) gene are viable and fertile. No Mmp9 activity is detected in spleen cell lysates. Long bones (tibia, femur) are 10% shorter in homozygous null mice. Histological examination of three-week-old mice reveals a dramatically lengthened zone of hypertrophic cartilage (six to eight times larger vs. wild-type) due to delayed apoptosis, vascularization, and ossification. Subsequent remodeling resolves the condition, resulting in normal appearing bones by eight weeks of age. Null mice show altered responses to repair of injury in skin, cornea, central nervous system and bone marrow reconstitution, and altered inflammatory responses. 
 Coat color expected from breeding is nonagouti. Of note, beginning ~mid-2021, The Jackson Laboratory live colony shows some homozygotes exhibit white belly spots in several pedigree lines throughout the colony. Because our colony is maintained by breeding homozygotes together, is not known if heterozygous mice have these spots [February 2023].
 In an attempt to offer alleles on well-characterized or multiple genetic backgrounds, alleles are frequently moved to a genetic background different from that on which an allele was first characterized. It should be noted that the phenotype could vary from that originally described. We will modify the strain description if necessary as published results become available.

Because Mmp9tm1Tvu homozygous mice show altered inflammatory responses they may be used to study injury response and repair, angiogenesis and inflammatory response.

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