Generating retinoic acid gradients by local degradation during craniofacial development: One cell's cue is another cell's poison

Retinoic acid (RA) is a vital morphogen for early patterning and organogenesis in the developing embryo. RA is a diffusible, lipophilic molecule that signals via nuclear RA receptor heterodimeric units that regulate gene expression by interacting with RA response elements in promoters of a significant number of genes. For precise RA signaling, a robust gradient of the morphogen is required. The developing embryo contains regions that produce RA, and specific intracellular concentrations of RA are created through local degradation mediated by Cyp26 enzymes. In order to elucidate the mechanisms by which RA executes precise developmental programs, the kinetics of RA metabolism must be clearly understood. Recent advances in techniques for endogenous RA detection and quantification have paved the way for mechanistic studies to shed light on downstream gene expression regulation coordinated by RA. It is increasingly coming to light that RA signaling operates not only at precise concentrations but also employs mechanisms of degradation and feedback inhibition to self‐regulate its levels. A global gradient of RA throughout the embryo is often found concurrently with several local gradients, created by juxtaposed domains of RA synthesis and degradation. The existence of such local gradients has been found especially critical for the proper development of craniofacial structures that arise from the neural crest and the cranial placode populations. In this review, we summarize the current understanding of how local gradients of RA are established in the embryo and their impact on craniofacial development.     

Phytotoxicity of soilborne glyphosate residues is influenced by the method of phosphorus fertiliser application

Plant and Soil - Glyphosate use has increased in recent decades with the adoption of minimum tillage techniques and the emergence of glyphosate-tolerant crop cultivars. There is evidence that...     

Indole acetic acid overproduction transformants of the rhizobacterium <Emphasis Type="Italic">Pseudomonas</Emphasis> sp. UW4

The plant growth-promoting rhizobacterium Pseudomonas sp. UW4 was transformed to increase the biosynthesis of the auxin, indole-3-acetic acid (IAA). Four native IAA biosynthesis genes from strain UW4 were individually cloned into an expression vector and introduced back into the wild-type strain. Quantitative real-time polymerase chain reaction analysis revealed that the introduced genes ami, nit, nthAB and phe were all overexpressed in these transformants. A significant increase in the production of IAA was observed for all modified strains. Canola plants inoculated with the modified strains showed enhanced root elongation under gnotobiotic conditions. The growth rate and 1-aminocyclopropane-1-carboxylate deaminase activity of transformant strains was lower compared to the wild-type. The indoleacetic acid biosynthesis pathways and the role of this phytohormone in the mechanism of plant growth stimulation by Pseudomonas sp. UW4 is discussed.     

Honest advocacy for nature: presenting a persuasive narrative for conservation

Conservation scientists are increasingly recognising the value of communicating policy-relevant knowledge to policy-makers. Whilst considerable progress has been made in offering practical advice for scientists seeking to engage more closely with decision-makers, researchers have provided few tangible examples to learn from. This paper uses an English case study, but draws out important high-level messages relevant to conservation scientists worldwide. The case study looks at how the Lawton Review presented knowledge persuasively about the suitability of England’s ecological network to deal with future pressures. Through skilful framing of rigorous scientific knowledge it was able to make a significant impact on government policy. Impact was achieved through: (1) selecting politically salient frames through which to communicate; (2) using clear, accessible language, and; (3) conducting rigorous science using an authoritative team of experts. Although its publication coincided with a favourable policy window, the Lawton Review seized on this opportunity to communicate a rigorously argued, persuasive and practical conservation message; in other words, it performed ‘honest advocacy’. Thus, whilst it remains important to conduct scientific research with technical rigour, conservation scientists could also benefit from identifying salient frames for conservation and communicating clearly.     

Giant congenital melanocytic nevus with vascular malformation and epidermal cysts associated with a somatic activating mutation in BRAF

Giant congenital melanocytic nevi may be symptomatically isolated or syndromic. Associations with capillary malformations are exceptional, and development of epidermal cysts has not been described. A 71‐year‐old patient with a giant congenital melanocytic nevus (CMN) of the lower back, buttocks, and thighs was asymptomatic except for unexpected hemorrhage during partial surgical excision years before. Blunt trauma at age 64 initiated recurrent, severe pain under the nevus; multiple large epidermal cysts then developed within it. Imaging and biopsy showed a large, non‐pulsatile venous malformation intermingled with the deep nevus. A low‐abundance, heterozygous BRAF c.1799T>A (p.V600E) mutation was present in both gluteal and occipital congenital nevi; additional mutations in NRAS, GNAQ, GNA11, HRAS, or PIK3CA were undetectable. This is the first demonstration of a recurrent BRAF mutation in multiple large congenital nevi from the same individual, confirming that this malformation can have multiple genetic origins. Early constitutive activation of BRAF can therefore cause unusual associations of giant nevi with vascular malformations, indicating that both pigment and endothelial cell physiology may be affected by mosaic RASopathies.     

COMPLEX TRADE-OFFS AND THE EVOLUTION OF STARVATION RESISTANCE IN DROSOPHILA MELANOGASTER

The measurement of trade-offs may be complicated when selection exploits multiple avenues of adaptation or multiple life-cycle stages. We surveyed 10 populations of Drosophila melanogaster selected for increased resistance to starvation for 60 generations, their paired controls, and their mutual ancestors (a total of 30 outbred populations) for evidence of physiological and life-history trade-offs that span life-cycle stages. The directly selected lines showed an impressive response to starvation selection, with mature adult females resisting starvation death 4–6 times longer than unselected controls or ancestors—up to a maximum of almost 20 days. Starvation-selected flies are already 80% more resistant to starvation death than their controls immediately upon eclosion, suggesting that a significant portion of their selection response was owing to preadult growth and acquisition of metabolites relevant to the stress. These same lines exhibited significantly longer development and lower viability in the larval and pupal stages. Weight and lipid measurements on one of the starvation-selected treatments (SB_1–5), its control populations (CB_1–5), and their ancestor populations (B_1–5) revealed three important findings. First, starvation resistance and lipid content were linearly correlated; second, larval lipid acquisition played a major role in the evolution of adult starvation resistance; finally, increased larval growth rate and lipid acquisition had a fitness cost exacted in reduced viability and slower development. This study implicates multiple life-cycle stages in the response to selection for the stress resistance of only one stage. Our starvation-selected populations illustrate a case that may be common in nature. Patterns of genetic correlation may prove misleading unless multiple pleiotropic interconnections are resolved.     

Time-Dependent Increase in Release of Arachidonic Acid Following Passive Avoidance Training in the Day-Old Chick

Abstract: We have investigated the role of arachidonic acid, a putative retrograde messenger, in a one-trial aversive learning task in the day-old chick. The left and right intermediate medial hyperstriatum ventrale (IMHV) in the chick forebrain have previously been implicated in the formation of memory for this task. Using an ex vivo technique we have determined the concentrations of various fatty acids liberated from prisms prepared from these brain regions at different time points up to 24 h following passive avoidance training. At 30, 60, and 75 min post-training the concentration of arachidonic acid, but not of other fatty acids, in prisms prepared from the left IMHV, but not the right IMHV, was enhanced compared with that in chicks trained on a nonaversive water-coated bead. To test whether arachidonic acid liberation from the left IMHV was receptor-stimulated we showed that (a) liberation of endogenous arachidonic acid from homogenate prepared from the left and right IMHV of untrained chicks was stimulated by depolarization with KCl (50 m M ) and that (b) glutamate agonists of the NMDA and metabotropic subtypes of glutamate receptor stimulated release of preloaded [¹⁴C]arachidonic acid from prisms prepared from the left IMHV but not the right IMHV. These results indicate that arachidonic acid is liberated from the left IMHV following passive avoidance training in the day-old chick and may play a role as a retrograde messenger in this memory task.     

Volatile Semiochemicals Released from Undamaged Cotton Leaves (A Systemic Response of Living Plants to Caterpillar Damage)

Cotton plants (Gossypium hirsutum L.), attacked by herbivorous insects release volatile semiochemicals (chemical signals) that attract natural enemies of the herbivores to the damaged plants. We found chemical evidence that volatiles are released not only at the damaged site but from the entire cotton plant. The release of volatiles was detected from upper, undamaged leaves after 2 to 3 d of continuous larval damage on lower leaves of the same plant. Compounds released systemically were (Z)-3-hexenyl acetate, (E)-[beta]-ocimene, linalool, (E)-4,8-dimethyl-1,3,7-nonatriene, (E)-[beta]-farnesene, (E,E)-[alpha]-farnesene, and (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene. All systemically released compounds are known to be induced by caterpillar damage and are not released in significant amounts by undamaged plants. Other compounds, specifically indole, isomeric hexenyl butyrates, and 2-methylbutyrates, known to be released by cotton in response to caterpillar damage, were not released systemically. However, when upper, undamaged leaves of a caterpillar-damaged plant were damaged with a razor blade, they released isomeric hexenyl butyrates, 2-methylbutyrates, and large amounts of constitutive compounds in addition to the previously detected induced compounds. Control plants, damaged with a razor blade in the same way, did not release isomeric hexenyl butyrates or 2-methylbutyrates and released significantly smaller amounts of constitutive compounds. Indole was not released systemically, even after artificial damage.