Level-specific role of paraxial mesoderm in regulation of Tbx5/Tbx4 expression and limb initiation.
Tetrapod limbs, forelimbs and hindlimbs, emerge as limb buds during development from appropriate positions along the rostro-caudal axis of the main body. In this study, tissue interactions by which rostro-caudal level-specific limb initiation is established were analyzed. The limb bud originates from the lateral plate located laterally to the paraxial mesoderm, and we obtained evidence that level-specific tissue interactions between the paraxial mesoderm and the lateral plate mesoderm are important for the determination of the limb-type-specific gene expression and limb outgrowth. When the wing-level paraxial mesoderm was transplanted into the presumptive leg region, the wing-level paraxial mesoderm upregulated the expression of Tbx5, a wing marker gene, and down regulated the expression of Tbx4 and Pitx1, leg marker genes, in the leg-level lateral plate. The wing-level paraxial mesoderm relocated into the leg level also inhibited outgrowth of the hindlimb bud and down regulated Fgf10 and Fgf8 expression, demonstrating that the wing-level paraxial mesoderm cannot substitute for the function of the leg-level paraxial mesoderm in initiation and outgrowth of the hindlimb. The paraxial mesoderm taken from the neck- and flank-level regions also had effects on Tbx5/Tbx4 expression with different efficiencies. These findings suggest that the paraxial mesoderm has level-specific abilities along the rostro-caudal axis in the limb-type-specific mechanism for limb initiation.
Department of Developmental Biology and Neurosciences, Graduate School of Life Sciences, Tohoku University, Aobayama Aoba-ku, Sendai 980-8578, Japan.
Daisuke
D
Saito
Sayuri
S
Yonei-Tamura
Yoshiko
Y
Takahashi
Koji
K
Tamura
D000818:Animals; D030161:Avian Proteins / Q000096:biosynthesis* / Q000235:genetics; D002642:Chick Embryo; D015536:Down-Regulation / Q000235:genetics; D051526:Fibroblast Growth Factor 10 / Q000037:antagonists & inhibitors / Q000235:genetics; D051524:Fibroblast Growth Factor 8 / Q000037:antagonists & inhibitors / Q000235:genetics; D006614:Hindlimb / Q000196:embryology / Q000254:growth & development; D035002:Lower Extremity / Q000196:embryology* / Q000254:growth & development; D008648:Mesoderm / Q000502:physiology* / Q000637:transplantation; D009924:Organ Culture Techniques; D051761:Paired Box Transcription Factors / Q000037:antagonists & inhibitors / Q000235:genetics; D020825:T-Box Domain Proteins / Q000096:biosynthesis* / Q000235:genetics; D014921:Wings, Animal / Q000196:embryology* / Q000254:growth & development
D030161:Avian Proteins; D051526:Fibroblast Growth Factor 10; D051761:Paired Box Transcription Factors; D020825:T-Box Domain Proteins; C103172:T-box transcription factor 5; C491196:TBX4 protein, Gallus gallus; C101485:homeobox protein PITX1; D051524:Fibroblast Growth Factor 8