Related Experiment Video
Updated: Jan 7, 2026
Author Spotlight: Exploring Retinal Regeneration Mechanisms in the Xenopus Frog
Published on: October 13, 2023
All-trans retinoic acid-induced ectopic limb and caudal structures: murine strain sensitivities and pathogenesis
Xiaoyan Liao1, Michael D Collins
1Department of Environmental Health Sciences, University of California, Los Angeles, California 90095, USA.
Abstract:
Treatment of pregnant mice at the egg cylinder stage with retinoic acid (RA) has caused ectopic hindlimbs in the offspring. Proposed causes of ectopic hindlimbs include homeotic transformation or multiple axis formation. Two mouse strains were determined to be divergent in susceptibility to this malformation (C57BL/6N, highly sensitive; SWV/Fnn, less sensitive). Ectopic limbs were hindlimbs (expressing Pitx1 and Tbx4 but not Tbx5), yet they also expressed the predominantly forelimb Hoxb8. Ectopic body axis formation was indicated by gene expression for ectopic primitive streaks, notochords, and nodes, as well as inhibition of anterior visceral endoderm and mesodermal migration. The earlier in development that embryos were examined, the higher the rate of ectopic hindlimb development and axis formation. Ectopic axis formation and cell migration inhibition had the same strain susceptibility as the dysmorphogenesis. We propose that all extra hindlimbs were derived from ectopic axis formation, perturbation of which is genetic background dependent.
Insights
Retinoic acid (RA) exposure during early pregnancy can cause extra hindlimbs in offspring. This malformation is linked to ectopic body axis formation, with susceptibility varying by mouse strain.
Area of Science:
- Developmental Biology
- Teratology
- Genetics
Background:
- Retinoic acid (RA) is crucial for embryonic development.
- Exposure to RA during the egg cylinder stage can induce developmental abnormalities.
- Ectopic hindlimb formation is a known teratogenic effect of RA, with proposed mechanisms including homeotic transformation or multiple axis formation.
Purpose of the Study:
- To investigate the underlying mechanisms of retinoic acid-induced ectopic hindlimb formation in mice.
- To determine the role of ectopic axis formation in this developmental malformation.
- To explore genetic background-dependent susceptibility to RA-induced teratogenesis.
Main Methods:
- Treatment of pregnant mice (C57BL/6N and SWV/Fnn strains) with retinoic acid at the egg cylinder stage.
- Analysis of offspring for ectopic hindlimb development.
- Gene expression analysis (Pitx1, Tbx4, Tbx5, Hoxb8) to characterize ectopic limbs.
- Examination of embryonic development for indicators of ectopic axis formation (primitive streaks, notochords, nodes, anterior visceral endoderm, mesodermal migration).
Main Results:
- Retinoic acid treatment induced ectopic hindlimbs in offspring, with varying susceptibility between mouse strains (C57BL/6N > SWV/Fnn).
- Ectopic hindlimbs expressed hindlimb markers (Pitx1, Tbx4) but also a forelimb marker (Hoxb8).
- Evidence of ectopic body axis formation, including primitive streaks, notochords, and nodes, was observed, alongside inhibited anterior visceral endoderm and mesodermal migration.
- The rate of ectopic hindlimb and axis formation increased with earlier embryonic examination.
- Strain susceptibility for ectopic axis formation and cell migration inhibition mirrored that of hindlimb development.
Conclusions:
- Ectopic hindlimb formation induced by retinoic acid is primarily caused by ectopic axis formation, not homeotic transformation.
- Perturbation of ectopic axis formation and subsequent cell migration is dependent on the genetic background of the mouse strain.
- This study highlights the critical role of early embryonic patterning and genetic factors in teratogenic responses.
