Mice homozygous for the Klk4-null/lacZ knock-in allele (Klk4- or Klk4lacZ) are viable and fertile, with a nuclear-localized β-galactosidase (NLS lacZ) translation initiation site and coding region replacing the Klk4 translation initiation site and coding region. This abolishes endogenous gene function. Under control of the upstream promoter/enhancer elements, lacZ expression is directed to ameloblasts (the enamel-forming cells in developing teeth) during the transition and maturation stages of dental enamel formation. Klk4-deficiency results in improper dental enamel matrix biomineralization, altered gross tooth morphology, and premature tooth decay. Homozygous mice exhibit malformed enamel that is rapidly abraded after weaning (even when fed moistened chow) and a tendency for all teeth to fracture at points of contact. Heterozygous mice appear indistinguishable from wildtype mice. These Klk4lacZ mice may be useful for studying the molecular mechanisms of enamel protein cleavage necessary for proper dental enamel formation/biomineralization/crystallization during tooth development.
NLS lacZ activity may be readily distinguished from native mouse lacZ activity by its nuclear localization and high pH optima: mouse β-galactosidase is a lysosomal enzyme that is only marginally active at pH 7.5, whereas bacterial β-galactosidase can be strongly detected above pH 8 (Weiss et al, 1999 Histochem J 31:231).
