Home About us Contact
|
Home About us Contact | ||
|
|
||
Knockout Experiments (knockout + experiment)
Selected AbstractsMolecular insights into insulin action and secretionEUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 2002C. J. Rhodes Abstract Tightly co-ordinated control of both insulin action and secretion is required in order to maintain glucose homeostasis. Gene knockout experiments have helped to define key signalling molecules that affect insulin action, including insulin and insulin-like growth factor-1 (IGF-1) receptors, insulin receptor substrate (IRS) proteins and various downstream effector proteins. ,-cell function is also a tightly regulated process, with numerous factors (including certain signalling molecules) having an impact on insulin production, insulin secretion and ,-cell mass. While signalling molecules play important roles in insulin action and secretion under normal circumstances, abnormal insulin signalling in muscle, adipose tissue, liver and pancreas leads to insulin resistance and ,-cell dysfunction. In particular, the signalling protein IRS-2 may have a central role in linking these abnormalities, although other factors are likely to be involved. [source] Genetic evidence for Dnmt3a-dependent imprinting during oocyte growth obtained by conditional knockout with Zp3 -Cre and complete exclusion of Dnmt3b by chimera formationGENES TO CELLS, Issue 3 2010Masahiro Kaneda In the male and female germ-lines of mice, both of the two de novo DNA methyltransferases Dnmt3a and Dnmt3b are expressed. By the conditional knockout experiments using the Tnap -Cre gene, we previously showed that deletion of Dnmt3a in primordial germ cells disrupts paternal and maternal imprinting, however, Dnmt3b mutants did not show any defect. Here, we have knocked out Dnmt3a after birth in growing oocytes by using the Zp3 -Cre gene and obtained genetic evidence that de novo methylation by Dnmt3a during the oocyte growth stage is indispensable for maternal imprinting. We also carried out DNA methylation analysis in the mutant oocytes and embryos and found that hypomethylation of imprinted genes in Dnmt3a -deficient oocytes was directly inherited to the embryos, but repetitive elements were re-methylated during development. Furthermore, we show that Dnmt3b -deficient cells can contribute to the male and female germ-lines in chimeric mice and can produce normal progeny, establishing that Dnmt3b is dispensable for mouse gametogenesis and imprinting. Finally, Dnmt3-related protein Dnmt3L is not only essential for methylation of imprinted genes but also enhances de novo methylation of repetitive elements in growing oocytes. [source] Interpretation of knockout experiments: the congenic footprintGENES, BRAIN AND BEHAVIOR, Issue 3 2007L. C. Schalkwyk In gene targeting experiments, the importance of genetic background is now widely appreciated, and knockout alleles are routinely backcrossed onto a standard inbred background. This produces a congenic strain with a substantial segment of embryonic stem (ES)-cell-derived chromosome still flanking the knockout allele, a phenomenon often neglected in knockout studies. In cholecystokynin 2 (Cckbr) knockout mice backcrossed with C57BL/6, we have found a clear ,congenic footprint' of expression differences in at least 10 genes across 40 Mb sequence flanking the Cckbr locus, each of which is potentially responsible for aspects of the ,knockout' phenotype. The expression differences are overwhelmingly in the knockout-low direction, which may point to a general phenomenon of background dependence. This finding emphasizes the need for caution in using gene knockouts to attribute phenotypic effects to genes. This is especially the case when the gene is of unknown function or the phenotype is unexpected, and is a particular concern for large-scale knockout and phenotypic screening programmes. However, the impact of genetic background should not be simply viewed as a potential confound, but as a unique opportunity to study the broader responses of a system to a specific (genetic) perturbation. [source] Regulation, necessity, and the misinterpretation of knockoutsBIOESSAYS, Issue 8 2009Jamie Davies Abstract Much contemporary biology consists of identifying the molecular components that associate to perform biological functions, then discovering how these functions are controlled. The concept of control is key to biological understanding, at least of the physiological kind; identifying regulators of processes underpins ideas of causality and allows complicated, multicomponent systems to be summarized in relatively simple diagrams and models. Unfortunately, as this article demonstrates by drawing on published articles, there is a growing tendency for authors to claim that a molecule is a ,regulator' of something on evidence that cannot support the conclusion. In particular, gene knockout experiments, which can demonstrate only that a molecule is necessary for a process, are all too frequently being misinterpreted as revealing regulation. This logical error threatens to blur the important distinction between regulation and mere necessity and therefore to weaken one of our strongest tools for comprehending how organisms work. [source] | ||||||||||