Fig. 5.

3-Hydroxynorvaline arrests the early development of mouse embryos. Blastocyst-stage mouse embryos were assayed by in situ hybridization to localize TDH mRNA (A) and immunohistochemical staining with antibodies specific to the TDH enzyme (B). In situ and antibody staining signals localized the TDH mRNA (purple) and enzyme (green) to cells associated with the ICM. Precompacted morula-stage embryos were incubated in varying concentrations of the threonine analog 3-HNV. Embryos exposed to 1 mM and 300 μM 3-HNV were blocked from forming cavitated blastocysts (C). Incubation with 4 mM threonine resulted in complete rescue of embryonic development even at the highest concentration (1 mM) of 3-HNV.