Skip to content
Login Register

#forelimb development

3 public questions tagged with this topic.

Limb Development -ll

Which gene acts downstream of TBX5 in forelimb formation?

Forelimb developmental cascade begins with axial retinoic acid and Hox signals inducing TBX5 in rostral lateral plate mesoderm. TBX5 directly binds Tbx5-responsive enhancer of FGF10 to activate transcription and trigger budding via MAPK. FGF10 then induces FGF8 in AER, linking specification to outgrowth feedback loop involving Wnt3a. Therefore FGF10 functions genetically downstream of TBX5; TBX5 mutants fail to express FGF10 in forelimb field and forelimbs absent. FGF8 lies downstream of FGF10, SHH downstream later for AP pattern, BMP4 later for apoptosis. Thus molecular hierarchy is TBX5 then FGF10 then FGF8.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 20: TBX5 to FGF10 pathway in forelimb.

View Details
Tetrapod

Which molecule regulates limb identity by distinguishing forelimbs from hindlimbs?

Morphological distinction between forelimb and hindlimb including muscle, tendon, bone patterns is orchestrated by Pitx1 homeodomain factor restricted to posterior lateral plate mesoderm and hindlimb buds. Pitx1 directly activates Tbx4, Hoxc10, and influences cell adhesion, cartilage nodule organization. Transgenic misexpression of Pitx1 in forelimb induces hindlimb-like musculature and skeletal transformations, upregulates hindlimb markers, whereas Tbx4 misexpression alone insufficient for full conversion. Pitx1 knockout causes hindlimb to acquire forelimb-like features including patella loss. Thus Pitx1 functions as master determinant distinguishing hindlimb identity.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 19: Pitx1 as determinant of hindlimb morphological identity.

View Details
Tetrapod

Which transcription factor is responsible for forelimb development in tetrapods?

Forelimb determination depends on T-box transcription factor TBX5 expressed in anterior lateral plate mesoderm rostral to hindlimb region. TBX5 directly activates Fgf10 transcription in forelimb field progenitors, triggering downstream Wnt3a and Fgf8 in ectoderm and establishing self-sustaining outgrowth loop. TBX5 loss-of-function mutations cause Holt-Oram syndrome featuring thumb and radial defects plus cardiac septal anomalies reflecting cardiac co-expression. Homozygous mouse knockout eliminates forelimb bud induction completely while hindlimbs remain normal, proving specific requirement. Ectopic TBX5 can induce additional wing-like bud in interlimb region experimentally.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 19: TBX5 in forelimb specification and Holt-Oram syndrome.

View Details