Animals have evolved limb proportions adapted to different environments, but it is not yet clear to what extent these proportions are directly influenced by the environment during prenatal development. The developing skeleton experiences mechanical loading resulting from embryo movement. We tested the hypothesis that environmentally-induced changes in prenatal movement influence embryonic limb growth to alter proportions. We show that incubation temperature influences motility and limb bone growth in West African Dwarf crocodiles, producing altered limb proportions which may, influence post-hatching performance. Pharmacological immobilisation of embryonic chickens revealed that altered motility, independent of temperature, may underpin this growth regulation. Use of the chick also allowed us to merge histological, immunochemical and cell proliferation labelling studies to evaluate changes in growth plate organisation, and unbiased array profiling to identify specific cellular and transcriptional targets of embryo movement. This disclosed that movement alters limb proportions and regulates chondrocyte proliferation in only specific growth plates. This selective targeting is related to intrinsic mTOR (mechanistic target of rapamycin) pathway activity in individual growth plates. Our findings provide new insights into how environmental factors can be integrated to influence cellular activity in growing bones and ultimately gross limb morphology, to generate phenotypic variation during prenatal development.

Children and young adults with glioblastoma (GBM) have a median survival rate of only 12 to 15 months, and these GBMs are clinically and biologically distinct from histologically similar cancers in older adults. They are defined by highly specific mutations in the gene encoding the histone H3.3 variant H3F3A, occurring either at or close to key residues marked by methylation for regulation of transcription—K27 and G34. Here, we show that the cerebral hemisphere-specific G34 mutation drives a distinct expression signature through differential genomic binding of the K36 trimethylation mark (H3K36me3). The transcriptional program induced recapitulates that of the developing forebrain, and involves numerous markers of stem-cell maintenance, cell-fate decisions, and self-renewal. Critically, H3F3A G34 mutations cause profound upregulation of MYCN, a potent oncogene that is causative of GBMs when expressed in the correct developmental context. This driving aberration is selectively targetable in this patient population through inhibiting kinases responsible for stabilization of the protein. Significance: We provide the mechanistic explanation for how the first histone gene mutation in human disease biology acts to deliver MYCN, a potent tumorigenic initiator, into a stem-cell compartment of the developing forebrain, selectively giving rise to incurable cerebral hemispheric GBM. Using synthetic lethal approaches to these mutant tumor cells provides a rational way to develop novel and highly selective treatment strategies. Cancer Discov; 3(5); 512–19. ©2013 AACR. See related commentary by Huang and Weiss, p. 484 This article is highlighted in the In This Issue feature, p. 471