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The regulatory landscape controlling Hoxd gene expression in tetrapod digit development was probably co-opted from a pre-existing cloacal regulatory mechanism, as evidenced by the effects of genetic deletion experiments in zebrafish fin, cloaca and mouse urogenital development.

The organization of Hox clusters in several different reptiles is investigated, showing that the Hox clusters in squamates — lizards and snakes — have unexpectedly accumulated transposable elements, reflecting extensive genomic rearrangements of coding and non coding regulatory regions. Comparative expression analyses between two species showing different axial skeletons, the corn snake and the whiptail lizard, revealed major alterations in Hox13 and Hox10 expression features during snake somitogenesis, in line with the expansion of both caudal and thoracic regions.

Cultures grown from small aggregates of mouse embryonic stem cells can be induced to organize spatial and temporal patterns of gene expression that parallel those of the early embryo, offering a potentially useful system for studying early development.

Temporal activation of Hox genes in mouse pseudo-embryos in vitro initiates at the anterior part of the cluster and is accompanied by asymmetric loading of cohesin. Posterior CTCF sites then successively act as transient insulators, regulating the timed transcription of more posterior-located genes.

Hoxd genes are needed for the formation of sphincters to subdivide the developing gut.

Here the authors show that a strong enhancer sequence can be controlled by the chromatin environment provided by a topologically associated domain (TAD) located nearby. An enhancer relocated by homologous recombination takes all the hallmarks of its new neighboring enhancers located in the recipient TAD.

Mesomelic dysplasia, a severe shortening and bending of the limb, has been linked to rearrangements in the HoxD cluster in humans and mice. Here the authors engineer a 1 Mb inversion including the HoxD gene cluster and use this model to provide a mechanistic framework to understand and unify the molecular origins of human mesomelic dysplasia associated with 2q31.

What is the developmental mechanism that makes our upper arms different from our forearms or fingers? Two new papers challenge an influential and popular model, and propose an alternative view.

MicroRNAs are important in the development of worms, flies and plants. A new study shows how the temporal and spatial expression patterns of such RNAs can be determined in mouse embryos, providing insights into the emerging role of microRNAs in Hox gene regulation.

The Hox gene family contains 39 related genes that are crucial for development in mammals. By swapping the protein-coding regions of Hox genes around, it has been shown that the function of a Hox gene may depend not on which protein it produces, but on where, when and how strongly it is expressed.

Homeobox genes have some quirky features: they huddle together and tend to be expressed in the order that they appear in their cluster. A new cluster, specific to reproductive development, has now been discovered.

The basic five-digit limb of tetrapods has been altered many times during evolution, usually by the progressive loss of digits — this study tracks the molecular underpinnings of this change, showing that in comparison to mouse, the polarized gene expression in the bovine limb bud is progressively lost due to evolutionary alteration of the cis-regulatory sequences that control Ptch1 expression in response to SHH signalling in the digit-forming handplate.

The European Mouse Mutagenesis Consortium is the European initiative contributing to the international effort on functional annotation of the mouse genome. Its objectives are to establish and integrate mutagenesis platforms, gene expression resources, phenotyping units, storage and distribution centers and bioinformatics resources. The combined efforts will accelerate our understanding of gene function and of human health and disease.

There are now myriad variations on techniques to reprogramme somatic cells into pluripotent stem cells, but which options should researchers choose? This Review sets out the choices, focusing on how the desired downstream application should guide the reprogramming strategy.

How are the complex and varied roles of retinoic acid orchestrated at multiple developmental stages? Recent studies have highlighted the importance of tightly regulating its distribution, of switching the activities of its nuclear receptors, and of interactions with other key developmental signalling molecules.

How left–right asymmetries are established in vertebrate embryos has fascinated developmental biologists for decades. Recent evidence from a range of species provides insights into the genetic and epigenetic mechanisms that are involved, particularly in the early stages of generating left–right asymmetry.