Differences between NMRI and DBA/2J mice in the development of somites and susceptibility to methylnitrosourea-induced skeleton anomalies

Abstract

The development of DBA/2J mouse strain embryos is nearly 12 h -or 6 somite pairs -delayed as compared to the outbred NMRI mouse embryos of the same age on gestation days (GD) 8-12. To evaluate interstrain differences in susceptibility to teratogens, dams were treated with methylnitrosourea (MNU, 5 mg/kg body weight i.p.) on defined gestation days (NMRI: GD 9, 9 1/2 or 10; DBA/2J: GD 10 or 10). Skeletal anomalies produced by MNU on both mouse strains varied with the GD of treatment. The pattern of anomalies produced by MNU on a given GD markedly differed between the two mouse strains, yet they were similar -with a few exceptions-when exposures at equivalent embryonic stages are compared. Findings from this study indicated that strain-dependent differences in the developmental stage of mouse embryos of the same gestational age occur, a possibility that has been often neglected when inter-strain differences in susceptibility to developmental toxicants are interpreted.