Biomechanics and the thermotolerance of development

Successful completion of development requires coordination of patterning events with morphogenetic movements. Environmental variability challenges this coordination. For example, developing organisms encounter varying environmental temperatures that can strongly influence developmental rates. We hypothesized that the mechanics of morphogenesis would have to be finely adjusted to allow for normal morphogenesis across a wide range of developmental rates. We formulated our hypothesis as a simple model incorporating time-dependent application of force to a viscoelastic tissue. This model suggested that the capacity to maintain normal morphogenesis across a range of temperatures would depend on how both tissue viscoelasticity and the forces that drive deformation vary with temperature. To test this model we investigated how the mechanical behavior of embryonic tissue (Xenopus laevis) changed with temperature; we used a combination of micropipette aspiration to measure viscoelasticity, electrically induced contractions to measure cellular force generation, and confocal microscopy to measure endogenous contractility. Contrary to expectations, the viscoelasticity of the tissues and peak contractile tension proved invariant with temperature even as rates of force generation and gastrulation movements varied three-fold. Furthermore, the relative rates of different gastrulation movements varied with temperature: the speed of blastopore closure increased more slowly with temperature than the speed of the dorsal-to-ventral progression of involution. The changes in the relative rates of different tissue movements can be explained by the viscoelastic deformation model given observed viscoelastic properties, but only if morphogenetic forces increase slowly rather than all at once. © 2014 von Dassow et al

Implications for dorsoventral axis determination from the zebrafish mutation janus

THE mechanisms underlying the formation of dorsoventral polarity in the zebrafish Danio rerio are unknown. Here we describe the zebrafish recessive maternal-effect mutation janusm55. The mutant phenotype is a division of the blastoderm along the first cleavage plane into two detached half-sized blastoderms. Partial-axis bifurcation occurs in a subset of mutants. Analysis of goosecoid expression in the mutant embryos indicates that only one organizer region is present in each embryo. Furthermore, the position of this organizer region is random with respect to the first cleavage plane bisecting the two blastoderms. Finally, cell tracing in wild-type embryos demonstrates that there is no strict correlation of the dorsoventral axis with early cleavage planes in zebrafish. These findings support the notion that the establishment of the dorsoventral axis and the first cleavage planes are determined by separate mechanisms in the zebrafish embryo

DNA methyltransferases and stress-related genes expression in zebrafish larvae after exposure to heat and copper during reprogramming of DNA methylation

DNA methylation, a well-studied epigenetic mark, is important for gene regulation in adulthood and for development. Using genetic and epigenetic approaches, the present study aimed at evaluating the effects of heat stress and copper exposure during zebrafish early embryogenesis when patterns of DNA methylation are being established, a process called reprogramming. Embryos were exposed to 325 μg Cu/L from fertilization (&lt;1 h post fertilization-hpf) to 4 hpf at either 26.5 °C or 34 °C, followed by incubation in clean water at 26.5 °C till 96 hpf. Significant increased mortality rates and delayed hatching were observed following exposure to combined high temperature and Cu. Secondly, both stressors, alone or in combination, significantly upregulated the expression of de novo DNA methyltransferase genes (dnmt3) along with no differences in global cytosine methylation level. Finally, Cu exposure significantly increased the expression of metallothionein (mt2) and heat shock protein (hsp70), the latter being also increased following exposure to high temperature. These results highlighted the sensitivity of early embryogenesis and more precisely of the reprogramming period to environmental challenges, in a realistic situation of combined stressors.</p

Morphological and molecular data from Madeira support the persistence of an ancient lineage of Taxus baccata

Macaronesia is an important biodiversity hotspot in the Mediterranean bioclimatic region, hosting a number of endemics, and encompassing outstanding refugia for ancient Tertiary plant lineages. We investig past occurrence and present distribution of yew (Taxus baccata L.) in the Madeiran archipelago, providing preliminary morphological and genetic descriptions and addressing conservation issues. Fifty-eight individuals presently occur in 19 micro-populations, as probable survivors of the continued yew exploitation across the centuries. Plants were characterized and compared with Euro-Mediterranean provenances by leaf morphology, anatomy, nuclear ITS (Internal Trascribed Spacer) and plastid trnS-trnQ DNA markers. The Madeiran provenance showed peculiar leaf size and morpho-anatomical characters. DNA sequences revealed a basal position of Madeiran yew in the Baccata phylogenetic clades along with the Azorean provenance. Gathered data suggest the survival of a lineage of T. baccata different from those on the continent, and with a possible closer derivation from the species' ancestors. Such evidences provide a base for identifying a great phylo- and phytogeographical interest of the Macaronesian provenance, and confirm the role of the archipelagos to preserve relict flora and lineages. The risk of extinction of Madeiran yew also calls for conservation strategies and restoration programs for a prompt species rescue. © 2013 Copyright Dipartimento di Biologia Evoluzionistica, Università di Firenze.s