Many animals alter their reproductive strategies in response to environmental stress. Here we have investigated how L4 hermaphrodites of Caenorhabditis elegans respond to starvation. To induce ...starvation, we removed food at 2 h intervals from very early- to very late-stage L4 animals. The starved L4s molted into adulthood, initiated oogenesis, and began producing embryos; however, all three processes were severely delayed, and embryo viability was reduced. Most animals died via 'bagging,' because egg-laying was inhibited, and embryos hatched in utero, consuming their parent hermaphrodites from within. Some animals, however, avoided bagging and survived long term. Long-term survival did not rely on embryonic arrest but instead upon the failure of some animals to produce viable progeny during starvation. Regardless of the bagging fate, starved animals showed two major changes in germline morphology: All oogenic germlines were dramatically reduced in size, and these germlines formed only a single oocyte at a time, separated from the remainder of the germline by a tight constriction. Both changes in germline morphology were reversible: Upon re-feeding, the shrunken germlines regenerated, and multiple oocytes formed concurrently. The capacity for germline regeneration upon re-feeding was not limited to the small subset of animals that normally survive starvation: When bagging was prevented ectopically by par-2 RNAi, virtually all germlines still regenerated. In addition, germline shrinkage strongly correlated with oogenesis, suggesting that during starvation, germline shrinkage may provide material for oocyte production. Finally, germline shrinkage and regeneration did not depend upon crowding. Our study confirms previous findings that starvation uncouples germ cell proliferation from germline stem cell maintenance. Our study also suggests that when nutrients are limited, hermaphrodites scavenge material from their germlines to reproduce. We discuss our findings in light of the recently proposed state of dormancy, termed Adult Reproductive Diapause.
Bose-Einstein Condensation in Microgravity van Zoest, T; Gaaloul, N; Singh, Y ...
Science (American Association for the Advancement of Science),
06/2010, Letnik:
328, Številka:
5985
Journal Article
Recenzirano
Albert Einstein's insight that it is impossible to distinguish a local experiment in a "freely falling elevator" from one in free space led to the development of the theory of general relativity. The ...wave nature of matter manifests itself in a striking way in Bose-Einstein condensates, where millions of atoms lose their identity and can be described by a single macroscopic wave function. We combine these two topics and report the preparation and observation of a Bose-Einstein condensate during free fall in a 146-meter-tall evacuated drop tower. During the expansion over 1 second, the atoms form a giant coherent matter wave that is delocalized on a millimeter scale, which represents a promising source for matter-wave interferometry to test the universality of free fall with quantum matter.
Many types of adult stem cells exist in a state of cell-cycle quiescence, yet it has remained unclear whether quiescence plays a role in maintaining the stem cell fate. Here we establish the adult ...germline of Caenorhabditis elegans as a model for facultative stem cell quiescence. We find that mitotically dividing germ cells--including germline stem cells--become quiescent in the absence of food. This quiescence is characterized by a slowing of S phase, a block to M-phase entry, and the ability to re-enter M phase rapidly in response to re-feeding. Further, we demonstrate that cell-cycle quiescence alters the genetic requirements for stem cell maintenance: The signaling pathway required for stem cell maintenance under fed conditions--GLP-1/Notch signaling--becomes dispensable under conditions of quiescence. Thus, cell-cycle quiescence can itself maintain stem cells, independent of the signaling pathway otherwise essential for such maintenance.
We provide a summary of our results in three-dimensional, coordination-driven self-assembly based on the directional-bonding methodology, in which the stoichiometric mixing of complementary building ...blocks, with appropriate, predefined geometries, leads to targeted, nanoscopic cages. Using this motif, we have synthesized high-symmetry ensembles resembling the Platonic solids, such as dodecahedra, and the Archimedean solids, such as truncated tetrahedra and cuboctahedra, as well as other cages, like trigonal bipyramids, adamantanoids, and trigonal prisms. The synthesis and characterization of these compounds is discussed, as is some host-guest chemistry.
Most of the research efforts involving the bovine gastrointestinal microbiota have focused on cattle's forestomach, particularly the rumen, so information concerning the bovine fecal microbiota is ...more scarce, especially in young beef cattle. The present study was performed to evaluate the ruminal and fecal microbiotas of beef calves as they reached the end of their nursing phase. A total of 18 Angus cow/calf pairs were selected and assigned to one of two treatment groups for the last 92 days of the calves' nursing period, as follows: 1) calves were supplemented with concentrate in a creep feeding system; or 2) control group with no supplementation of calves. After 92 days, ruminal and fecal samples were individually obtained from calves in both groups, and their microbiotas were evaluated using 16S rRNA gene sequencing. Ruminal samples were predominated by Prevotella (18 to 23% of the total bacterial abundance), regardless if calves received supplementation or not; however, in the feces, Prevotella was only the seventh most abundant genus (0.6 to 2.1% of total bacterial abundance). Both the rumen (P = 0.01) and the feces (P = 0.05) of calves that received supplementation had greater abundance of Firmicutes. In addition, calves that were supplemented had lower abundance of Fibrobacteres (P = 0.03) in their rumens. Regardless if the calves were supplemented or not, Faith's Phylogenetic Diversity index (P ≤ 0.007) and total concentration of short chain fatty acids (P < 0.001) were both greater in the rumen than in the feces of calves. In summary, the ruminal and fecal microbiotas of weanling beef calves were considerably distinct. Additionally, supplementation with creep feed caused some significant changes in the composition of the gastrointestinal microbiota of the calves, especially in the rumen, where supplementation caused an increase in Firmicutes and a decrease in abundance of Fibrobacteres.
Many chemotherapeutic drugs are differentially effective from one patient to the next. Understanding the causes of this variability is a critical step towards the development of personalized ...treatments and improvements to existing medications. Here, we investigate sensitivity to a group of anti-neoplastic drugs that target topoisomerase II using the model organism Caenorhabditis elegans. We show that wild strains of C. elegans vary in their sensitivity to these drugs, and we use an unbiased genetic approach to demonstrate that this natural variation is explained by a methionine-to-glutamine substitution in topoisomerase II (TOP-2). The presence of a non-polar methionine at this residue increases hydrophobic interactions between TOP-2 and its poison etoposide, as compared to a polar glutamine. We hypothesize that this stabilizing interaction results in increased genomic instability in strains that contain a methionine residue. The residue affected by this substitution is conserved from yeast to humans and is one of the few differences between the two human topoisomerase II isoforms (methionine in hTOPIIα and glutamine in hTOPIIβ). We go on to show that this amino acid difference between the two human topoisomerase isoforms influences cytotoxicity of topoisomerase II poisons in human cell lines. These results explain why hTOPIIα and hTOPIIβ are differentially affected by various poisons and demonstrate the utility of C. elegans in understanding the genetics of drug responses.
Abstract
In this work, a Q-learning based supply temperature control approach for a demonstrator building is proposed. The purpose is to improve the temperature behaviour inside the building and to ...tackle comfort problems such as overheating and undercooling which cannot be coped with by the standard heating curve. The Q-learning controller considers predicted future weather data as system states. This can be shown to be superior to Q-learning controllers without weather prediction. Furthermore, in order for the controller to capture different thermal effects of different time constants, a cascaded control structure is designed: An inner Q-learning based controller deals with thermal effects of smaller time constants. It is wrapped by an outer slower Q-learning controller which can tackle effects of larger time constants. Therewith, further improvement of comfort can be achieved.
Due to consumer demand and changing welfare standards on health, ecology, equity, and safety concepts, poultry production has changed markedly over the past 20 y. One of the greatest changes to ...poultry production standards is now offering poultry limited access to the outdoors in alternative and organic poultry production operations. Although operations allowing access to the outdoors are still only a small portion of commercial poultry production, it may impact the gastrointestinal (GIT) health of the bird in different ways than birds raised under conventional management systems. The present review describes current research results in alternative systems by identifying how different poultry production operations (diet, environmental disruptive factors, diseases) impact the ecology and health of the GIT. Various research efforts will be discussed that illustrate the nutritional value of free-range forages and how forages could be beneficial to animal health and production of both meat and eggs. The review also highlights the need for potential interventions to limit diseases without using antibiotics. These alternatives could enhance both economics and sustainability in organic and free-range poultry production.
Diffuse invasion of the surrounding brain parenchyma is a major obstacle in the treatment of gliomas with various therapeutics, including anti-angiogenic agents. Here we identify the epi-/genetic and ...microenvironmental downregulation of ephrinB2 as a crucial step that promotes tumour invasion by abrogation of repulsive signals. We demonstrate that ephrinB2 is downregulated in human gliomas as a consequence of promoter hypermethylation and gene deletion. Consistently, genetic deletion of ephrinB2 in a murine high-grade glioma model increases invasion. Importantly, ephrinB2 gene silencing is complemented by a hypoxia-induced transcriptional repression. Mechanistically, hypoxia-inducible factor (HIF)-1α induces the EMT repressor ZEB2, which directly downregulates ephrinB2 through promoter binding to enhance tumour invasiveness. This mechanism is activated following anti-angiogenic treatment of gliomas and is efficiently blocked by disrupting ZEB2 activity. Taken together, our results identify ZEB2 as an attractive therapeutic target to inhibit tumour invasion and counteract tumour resistance mechanisms induced by anti-angiogenic treatment strategies.
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