Experimental analysis of the emergence of left-right asymmetry of the body axis in early postimplantation mouse embryos.
The lateral asymmetry of the body axis of mouse embryo is revealed first by the asymmetric expression of genes such as nodal, lefty2 and Pitx2 in the lateral plate mesoderm of the neurulating embryo and subsequently by the looping of the heart tube, the rotation of the body axis and situ solitus of specific visceral organs. Analysis of gene expression in the early gastrula shows that there is a transient asymmetric localization of the transcripts of Cerrl, Fgf8, Hesx1 and Hnf3beta gene in the anterior visceral endoderm, Otx2 and Sox2 in the epiblast and Lim1 in the nascent mesoderm. However, the asymmetric expression is not consistent and varies among the embryos, which may be reflecting the lability of the mechanism for specifying the laterality of the body axis during gastrulation. The plasticity of the process that determines laterality is further manifested by the ability to randomise the expression of the Pitx2 gene in the lateral plate mesoderm in embryos that are grown in vitro. The expression of laterality requires the presence of the node and its axial mesodermal derivatives. In mutant embryos that lack the node and in node-ablated embryos, the loss of the axial notochord is associated with isomerism of the body axis, which is revealed either by the expression of the Pitx2 gene in the lateral plate mesoderm of both sides of the body or the complete absence of expression. Our results are therefore consistent with the concept that the specification of the laterality of the body axis goes through a dynamic phase during gastrulation and the activity of the node and its derivatives is instrumental in the conferment of left-right identity of the embryonic tissues.
Tsang
T E
TE
Embryology Unit, Children's Medical Research Institute, Wentworthville, NSW, Australia.
Kinder
S J
SJ
Tam
P P
PP
D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins; D019521:Body Patterning / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000235:genetics; D004622:Embryo, Mammalian / Q000002:abnormalities / Q000502:physiology*; D047108:Embryonic Development; D005260:Female; D005326:Fetal Proteins; D051524:Fibroblast Growth Factor 8; D005346:Fibroblast Growth Factors / Q000235:genetics; D007839:Functional Laterality; D005775:Gastrula / Q000502:physiology; D018507:Gene Expression Regulation, Developmental; D051956:Goosecoid Protein; D024002:HMGB Proteins; D051542:Hepatocyte Nuclear Factor 3-beta; D018398:Homeodomain Proteins / Q000235:genetics; D060850:LIM-Homeodomain Proteins; D051379:Mice; D008815:Mice, Inbred Strains; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000235:genetics; D009687:Nuclear Proteins / Q000235:genetics; D009924:Organ Culture Techniques / Q000379:methods; D051857:Otx Transcription Factors; D051761:Paired Box Transcription Factors; D011247:Pregnancy; D012097:Repressor Proteins; D055748:SOXB1 Transcription Factors; D020825:T-Box Domain Proteins / Q000235:genetics; D015534:Trans-Activators / Q000235:genetics; D000072056:Transcription Factor HES-1; D014157:Transcription Factors / Q000235:genetics; D051879:Twist-Related Protein 1; D000097577:Homeobox Protein PITX2; D000098908:Brachyury Protein
D051792:Basic Helix-Loop-Helix Proteins; D004268:DNA-Binding Proteins; D005326:Fetal Proteins; D051524:Fibroblast Growth Factor 8; D005346:Fibroblast Growth Factors; D051956:Goosecoid Protein; D024002:HMGB Proteins; D051542:Hepatocyte Nuclear Factor 3-beta; D018398:Homeodomain Proteins; D060850:LIM-Homeodomain Proteins; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D051857:Otx Transcription Factors; D051761:Paired Box Transcription Factors; D012097:Repressor Proteins; D055748:SOXB1 Transcription Factors; D020825:T-Box Domain Proteins; D015534:Trans-Activators; D000072056:Transcription Factor HES-1; D014157:Transcription Factors; D051879:Twist-Related Protein 1; D000097577:Homeobox Protein PITX2; D000098908:Brachyury Protein; C496457:Fgf8 protein, mouse; C496503:Foxa2 protein, mouse; C497993:Gsc protein, mouse; C489736:HESX1 protein, human; C489734:Hes1 protein, mouse; C489733:Hesx1 protein, mouse; C499523:Lhx1 protein, mouse; C497660:Otx2 protein, mouse; C527783:Sox2 protein, mouse; C101485:homeobox protein PITX1; C433629:homeobox protein PITX3