ta/ta
Origin & History: Found in White Leghorn stock: Abbott,
UK et al. 1960 J Hered 51:194-202; received from Abbott in 1996.
Breed: Single Comb White Leghorn
Symbol: ta-2
Characteristics: Autosomal recessive, embryonic lethal
Description: Homozygotes have 9-10 syndactylous digits, none of which are recognizable as members of the normal digit complement; all long bones of the wing and leg are reduced with the most proximal being most affected..
ta/ta
Additional Information: ta-2
wing buds can be recognized at stage 18; leg buds at about stage 20.The
defect is localized in the mesoderm of the wing bud. (J Exp Zool 155:161-170,
1964) Normal asymmetry along the anteroposterior axis is never established
in ta-2 wing buds, and unlike normal wing buds, when the apex of
the ta-2 wing bud is excised and reattached in reverse A-P orientation,
duplicate wing tips do not form. Reciprocal exchanges between ta-2 and
normal wing buds show that ta-2 has functional polarizing regionand
that the ta-2 wing bud can respond to polarizing tissue from a normal wing
bud. (J Embryol exp Morph 31:735-746, 1974; Dev Dyn 193:40-48, 1992) In
normal limb buds, GHox-4.6 is expressed solely in the posterior
mesoderm, from which the digits and most of the other skeletal elements
arise; GHox-8, the anterior mesoderm which will not give rise to
skeletal elements. In ta-2 suppression of GHox-8 in the anterior
mesoderm and ectopic expression of GHox-4.6 precede formation
of extra digits in the preaxial tissue.Expression
of GHox-8 in the AER is not affected by ta-2.(Development
115:629-637, 1992) Consistent with the hypothesis that GHox-7 expression
is involved in the outgrowth-promoting effect of the AER, and may be required
for limb outgrowth to occur, ta-2 wing buds show Ghox-7 expression
throughout the expanded subridge mesoderm. (Differentiation 52:129-137,
1993)