Chimera X Download ^HOT^
Jude Hargrave
The term "chimera" has come to describe any mythical or fictional creature with parts taken from various animals, to describe anything composed of disparate parts or perceived as wildly imaginative, implausible, or dazzling.
Some western scholars of Chinese art, starting with Victor Segalen, use the word "chimera" generically to refer to winged leonine or mixed species quadrupeds, such as bixie, tianlu, and even qilin.[22]
I have used Dada2 for the denoising step. As I know Dada2 also includes removing chimera. I am wondering that it is necessary to remove chimera with qiime vsearch uchime-denovo after denosing by Dada2 or not?
Recently, I have read the workflow of Qiime 2 I recognize that Denoise with Dada2 will generate the ASVs. Therefore, I am wondering if I like to get OTUs, it is necessary to do denoise with Dada2 or not. In case I do not use denoising with Dada2, do I need to perform other steps to remove and/or correct noisy reads and chimera? As you mentioned if I use Dada2, I do not need to do removing chimera. However, if I do not run Dada2 I still have to do removing chimera with vsearch uchime-denovo, is that right?
these files are analogous to those generated by qiime dada2 denoise-* and qiime deblur , except that no denoising, chimera removal, or other quality control has been applied in the dereplication process."
My sequence data is pre-quality checked so I dont use DADA2 or Deblur at this point. Where would I insert the chimera checking step into the pipeline? Any preference of which uchime method to use given my workflow?
Obviously, chimera check retains too many sequences with the default configuration. So, I have 2 questions: What could be a reason why I have so many declared chimeric sequences based on default? What parameters (--p-dn FLOAT,--p-mindiffs INTEGER RANGE,--p-mindiv FLOAT,--p-minh FLOAT,--p-xn FLOAT) can I tweak to soften the chimera-filtering and retain a higher proportion of my sequences?
Is there any recommendation for which database to use for uchime-ref for 16S primers targeting bacteria and archaea. In the literature I have seen the Silva Gold database (used by chimera slayer) and a database by the Broad Institute as part of their Microbiome Utilities package.
anything created by taking parts or aspects of different kinds of things and combining them: We are like an audio-art chimera, in that we act as part literary journal, part music showcase, and part storytelling podcast.
All animals develop from a single fertilised egg, so in theory every single cell in the body should have exactly the same genome. But chimeras can arise in several ways. The most dramatic is when two embryos that would normally develop into non-identical twins fuse in the womb. Parts of the resulting individual derive from one embryo and parts from another.
Several groups around the world are now trying to grow specific organs in another species, such as a human heart in a pig. The aim of this work is to provide organs for transplantation, but the creation of animal-human chimeras is controversial.
I was trying to do chimera removal using chimera.vsearch command but it does not detect any chimeras and does not create any count_table and fasta files. I got the following error message when the command got finished running.
(im an undergrad and a bit unexperienced with mothur so any help would be highly appreciated) (this is part of a mock test so I know that there should be chimeras that need to be removed)
All of the graphs except for the human population graph disappear, replaced by the graphs of a few dozen chimera species. Like demons, the graphs climb upward, all terminating in a single point, some higher, some lower.
One way to introduce xenogeneic stem cells into an embryo is by blastocyst injection, which refers to injecting stem cells into in vivo/vitro-cultured blastocyst cavities. Rat-mouse (6), human-mouse (7), and sheep-goat (8) chimeras with systemic chimerism are reported to be produced via blastocyst injection. However, blastocyst injection has failed to introduce stem cells into primate (such as rhesus monkey) embryos (9).
Chimeras may also result from the aggregation of two or more embryos either at equal or unequal stages. The quick and straightforward operation and low equipment cost make embryo aggregation an entry-level technique for chimera generation. Aggregation of rat-mouse (10), sheep-goat (11), and cattle-buffalo (12) embryos all form interspecies chimeras. Despite the lower survival rate of chimeric embryos produced by aggregation than by blastocyst injection, the chimerism rates have been observed to be higher (13,14). Considering that chimerism rates decide whether the human-animal chimeras can be an organ resource, aggregation is also a desirable choice when the embryo and stem cells are in a good growth condition.
The in utero transplanting of stem cells was an in utero treatment for congenital diseases at first (15). Now, it has become the most widely used experimental technique in human-animal chimera study. Human adult stem cells, including mesenchymal stem cells (MSCs) and hematopoietic stem cells (HSCs), can form chimeras in mouse, rat, pig, sheep or goat fetuses and contribute to multiple organs of the chimeras (16-21). In utero transplantation is reported to be the most efficient way to limit human cells in the target organ of human-animal chimera (22).
Nevertheless, several studies have demonstrated that human stem cells at asynchronous stages can also generate chimeras in animal embryos. Transplanting human adult stem cells (such as MSCs, neural stem cells and HSCs) into post-transplantation embryos of rat, sheep or goats (17,19,35), and into murine blastocysts can all generate chimeras (36). Moreover, compared to iPSCs, autologous adult stem cells have advantages such as easy accessibility, simple culture conditions, and less tumorigenicity (37).
Several recent studies also demonstrated that despite the equality of the developmental stage, the survival of injected stem cells is also crucial for chimerism. Both rat and human EpiSCs overexpressing anti-apoptotic genes (e.g., BCL2, BCL-XL, CRMA, BMI1, etc.) can form interspecies chimeras in mouse embryos (38-40). Meanwhile, adding anti-apoptotic reagent Y27632 (ROCK1 inhibitor) into culture medium also gives rise to chimerism of primate EpiSCs into morulae (41). Therefore, other proliferation-inducing and anti-apoptotic treatment, such as forced expression of SIRT1 (42), neurotrophin 3/4 (43) or Rho signaling pathway (44), might also impel chimera formation. Worryingly, however, apoptosis blockage in iPSCs might be more prone to tumorigenesis. In that case, more research is needed to assess the safety of increasing the chimerism rate through improving stem cell survival.
Apart from providing autologous organs, human-animal chimeras have additional benefits in clinical and experimental research. We might be able to produce therapeutic cells and functional proteins for clinical use. For instance, autologous HSCs in which pathogenic genes are edited might cure malignant hematological diseases with less immune rejection than allogeneic transplantation. Human cells overexpressing coagulation factor IX have been enriched in human-mouse chimeras, with the proteins being properly modified, secreted, and cleaved in vivo, thus being suitable for hemophilia B treatment (56). Although human-animal chimeras are still far away from clinical therapy, their application value in basic research has been undeniably proven in studies for human stem cell potency (20,21), cell fate during embryo early development and organogenesis (21), as well as in vivo models of human diseases (35) for drug metabolism study (57,58) and drug screening (48).
Recent advances in stem cells and gene engineering have paved the way for the generation of interspecies chimeras, such as animals bearing an organ from another species. The production of a rat pancreas by a mouse has demonstrated the feasibility of this approach. The next step will be the generation of larger chimeric animals, such as pigs bearing human organs. Because of the dramatic organ shortage for transplantation, the medical needs for such a transgressive practice are indisputable. However, there are serious technical barriers and complex ethical issues that must be discussed and solved before producing human organs in animals. The main ethical issues are the risks of consciousness and of human features in the chimeric animal due to a too high contribution of human cells to the brain, in the first case, or for instance to limbs, in the second. Another critical point concerns the production of human gametes by such chimeric animals. These worst-case scenarios are obviously unacceptable and must be strictly monitored by careful risk assessment, and, if necessary, technically prevented. The public must be associated with this ethical debate. Scientists and physicians have a critical role in explaining the medical needs, the advantages and limits of this potential medical procedure, and the ethical boundaries that must not be trespassed. If these prerequisites are met, acceptance of such a new, borderline medical procedure may prevail, as happened before for in-vitro fertilization or preimplantation genetic diagnosis.
One of the first embryological chimeras created by scientists was the result of landmark experiments carried out by Hans Spemann and Hilde Mangold, who grafted part of one amphibian (Triturus) embryo into another with a different degree of pigmentation [3]. Later, Nicole Le Douarin et al. [3] used chimeric embryos from chicken and quails for cell lineage tracking analyses during early vertebrate development. Alongside these man-made chimeras, natural chimeras have also been described. For instance, mothers might retain some of their fetus cells after pregnancy, a phenomenon called fetal microchimerism [4].
Concerning the production of chimeras, some ethical issues are closely tied to medical concerns. Indeed, one main worry is that the retroviruses integrated in the genome of animals could be transferred to humans. Indeed, the effects of these retroviruses might be known in animals, but there is no possibility of predicting what they could cause in humans. The fear is that human tissues produced in animals might be the source of new zoonoses, which brings up the ethical problems linked to the protection of human participants in clinical research to test the safety of such organs [21, 22]. Moreover, the impossibility to anticipate the potential risks associated with the transplantation of human organs grown in pigs calls for caution.
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