In:
eLife, eLife Sciences Publications, Ltd, Vol. 3 ( 2014-04-29)
Abstract:
Most animals are symmetrical about an imaginary line that runs from the head to the tail. A family of genes called the Hox family ensures that the cells in an animal embryo develop into the correct body parts along this head-to-tail axis. Hox genes—which are found in animals as diverse as flies and humans—are often clustered on the chromosomes, and their order within a cluster affects when and where each Hox gene is ‘switched on’. In mammals, Hox genes at one end of a cluster are switched on first and along almost the entire length of the embryo. Hox genes near the other end of the cluster are expressed later and only towards the hind end of the animal. And Hox genes at the furthest end of the cluster are expressed last and in the very tip of the developing tail. The time when a Hox gene is expressed depends largely on its relative position within the gene cluster. However, it is not clear how the ordering of the genes within a cluster is translated into a schedule whereby the genes are sequentially switched on during development. Much of the DNA in a chromosome is wrapped around proteins to form a structure called chromatin; chromatin is normally tightly packed, but ‘unpacking’ it allows the genes to be accessed and switched on. Now, Noordermeer et al. have used a technique called ‘circular chromosome conformation capture’ to follow how the packing of the chromosomes that carry the Hox gene clusters changes during embryonic development. Harvesting cells from mouse embryos of different ages, and cross-linking the DNA to the proteins, allowed those genes that are packed in the chromatin to be distinguished from those that have been unpacked and activated. When the embryo is still just a ball of almost identical cells, all the Hox genes are switched off and packed into inactive chromatin. However, Noordermeer et al. found that, as the embryo develops and when each Hox gene is switched on in turn, the relevant region of DNA is also unpacked and moved into more active chromatin. This mechanism likely prevents Hox genes that direct the development of the hind end of the mouse from being switched on too early, and hence it avoids body parts being misidentified and developing incorrectly. Further, the patterns of active chromatin vs inactive chromatin can be fixed at each section along head-to-tail axis, such that it will be memorized in all daughter cells produced subsequently from each particular body section. Future challenges will be to uncover the trigger behind the step-wise transition of every Hox gene from inactive chromatin to active chromatin, and to crack the underlying ‘clock’ that controls the timing of this process.
Type of Medium:
Online Resource
ISSN:
2050-084X
DOI:
10.7554/eLife.02557.001
DOI:
10.7554/eLife.02557.002
DOI:
10.7554/eLife.02557.003
DOI:
10.7554/eLife.02557.004
DOI:
10.7554/eLife.02557.005
DOI:
10.7554/eLife.02557.006
DOI:
10.7554/eLife.02557.007
DOI:
10.7554/eLife.02557.008
DOI:
10.7554/eLife.02557.009
DOI:
10.7554/eLife.02557.010
DOI:
10.7554/eLife.02557.011
DOI:
10.7554/eLife.02557.012
DOI:
10.7554/eLife.02557.013
DOI:
10.7554/eLife.02557.014
DOI:
10.7554/eLife.02557.015
DOI:
10.7554/eLife.02557.016
DOI:
10.7554/eLife.02557.017
DOI:
10.7554/eLife.02557.018
DOI:
10.7554/eLife.02557.019
DOI:
10.7554/eLife.02557.020
DOI:
10.7554/eLife.02557.021
DOI:
10.7554/eLife.02557.022
DOI:
10.7554/eLife.02557.023
DOI:
10.7554/eLife.02557.024
Language:
English
Publisher:
eLife Sciences Publications, Ltd
Publication Date:
2014
detail.hit.zdb_id:
2687154-3
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