体軸上で、四肢の出る位置はどのようにして決まるのか？

 

 

 

Patterning mechanisms controlling vertebrate limb development. J. Capdevila, J. C. I. Belmonte · 2001　脊椎動物の四肢芽では、シグナル伝達経路間の複雑な相互作用により、四肢の位置決め、成長、パターン形成が制御されます。　https://www.annualreviews.org/content/journals/10.1146/annurev.cellbio.17.1.87　本文有料 総説論文

 

Analysis of Hox gene expression in the chick limb bud. C. Nelson, Bruce A. Morgan, Ann C. Burke+7 more · 1996年5月1日　肢芽における Hox 遺伝子の発現は、肢の近位遠位節 (上腕、下腕、手) の指定とパターン形成に関連して、最大 3 つの独立した段階で制御されます。https://journals.biologists.com/dev/article/122/5/1449/39007/Analysis-of-Hox-gene-expression-in-the-chick-limb　Expression of the Hoxa genes during normal chick limb development. Whole mount in situ hybridizations to wings (upper row) and legs (lower row) for the genes: Hoxa-9 (A), Hoxa-10 (B), Hoxa-11 (C) and Hoxa-13 (D). Approximate stages are: stage 19/20, stage 23, stage 25 and stage 28 (from left to right). All panels are dorsal views with anterior to the top and distal to the right. (A) Hoxa-9 is expressed uniformly in limb mesenchyme at the earliest stages of limb bud outgrowth. By stage 19, there is a region in the anterior/proximal region of the wing bud that does not express Hoxa-9. This region, which does not express Hoxa-9, persists and expands through subsequent stages of development. Expression throughout the rest of the bud is strong through stage 23 and then fades slowly throughout the limb bud. By stage 25, only low levels of transcript are detected. By stage 28 expression is no longer detected in the limb. In the leg bud, Hoxa-9 expression parallels that in the wing, but there is no region of non-expressing tissue in the anterior/proximal region. (B) By stage 19 Hoxa-10 is expressed in the wing bud, but it is largely excluded from the marginal mesenchyme. By stage 22 Hoxa-10 is expressed at moderate levels throughout the wing mesenchyme with the exception of a region in the anterior/proximal portion of the wing. In the leg bud Hoxa-10 is expressed uniformly by stage 19 and never appears to be excluded from the anterior/proximal region seen in the wing. As development proceeds, progressively lower levels of transcript are detected throughout both limbs. At late stages, Hoxa-10 expression is still detectable in the upper arm/leg and lower arm/leg, but is largely absent from the hand/foot. (C) At early stages a region of expression is detected in the medial region of the wing bud, where scattered punctate staining is also observed. In late stage 19, a separate domain of expression along the distal margin of the wing is also observed. At stage 22, Hoxa-11 expression is observed in the distal half of the wing bud across the A/P axis of the limb. By stage 25, expression is restricted to the presumptive lower arm and is largely absent from the upper arm and hand. This pattern of expression persists through stage 28. By stage 19 Hoxa-11 expression in the distal margin of the leg bud is strong and uniform. Expression is also detected in more proximal regions, but in a less uniform, punctate pattern with higher levels observed in the posterior two thirds of the limb. By stage 22, expression is strong and uniform through most of the leg bud, although Hoxa-11 is not expressed in the proximal anterior region. At later stages, expression persists in the lower leg but is greatly reduced or absent in the upper leg and foot. This pattern persists through stage 28. Like many of the Hox genes, Hoxa-11 expression becomes excluded from regions of condensing cartilage. (D) Hoxa-13 is first expressed in the hind limb at stage 19 in the posterior distal mesenchyme. Expression in the fore limb begins shortly thereafter at the posterior distal margin (data not shown). Later, Hoxa-13 is expressed at high levels in a crescent along the distal margin of both limbs. By stage 25 expression is strong throughout the hand/foot with no obvious bias in expression level along the anterior/posterior axis; no Hoxa-13 expression is detected in the proximal segments of the limb. High levels of expression persist in the hand/foot through at least stage 28.