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Limb mesenchymal cells, when dissociated and grown in culture or reintroduced within ectodermal "hulls" can recapitulate essential aspects of pattern formation, morphogenesis and differentiation. [36] [37] Peculiarities of the limb skeletal pattern in the mouse Doublefoot mutant are predicted outcomes of a Turing-type mechanism. [38]
Patterning along the limb bud requires signals from many sources. Specifically, proteins called transcription factors (TF) help control the rate at which a gene is transcribed. The limb bud expresses a TF called ALX4 at the anterior part of the mesoderm, with the TF HOXB8 being expressed at the posterior portion. The Alx4 region, the medial ...
A sagittal plane (also known as anteroposterior plane) is perpendicular to the ground, separating left from right. The median (or midsagittal) plane is the sagittal plane in the middle of the body; it passes through midline structures such as the navel and the spine .
Signals that control anteroposterior neural development include FGF and retinoic acid, which act in the hindbrain and spinal cord. [16] The hindbrain, for example, is patterned by Hox genes , which are expressed in overlapping domains along the anteroposterior axis under the control of retinoic acid.
The pattern of Hox gene expression can be divided up into three phases throughout limb bud development, which corresponds to three key boundaries in proximal-distal limb development. The transition from the first phase to the second phase is marked by the introduction of Shh signals from the ZPA . [ 19 ]
The discovery of the homeobox in Drosophila flies and its conservation in other animals has led to advancements in understanding the anterior/posterior patterning. Most of the Hox genes in mammals show an expression pattern that parallels the homeotic genes in flies. In mammals, there are four copies of the Hox genes.
Wnt signaling is implicated in the formation of the anteroposterior and dorsoventral (DV) axes. Wnt signaling activity in anterior-posterior development can be seen in mammals, fish and frogs. In mammals, the primitive streak and other surrounding tissues produce the morphogenic compounds Wnts, BMPs , FGFs , Nodal and retinoic acid to establish ...
In anteroposterior (AP) views, the positions of the x-ray source and detector are reversed: the x-ray beam enters through the anterior aspect and exits through the posterior aspect of the chest. AP chest x-rays are harder to read than PA x-rays and are therefore generally reserved for situations where it is difficult for the patient to get an ...