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16.1A: The Process and Purpose of Gene Expression Regulation - Biology

16.1A: The Process and Purpose of Gene Expression Regulation - Biology



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Gene expression is a highly complex, regulated process that begins with DNA transcribed into RNA, which is then translated into protein.

Learning Objectives

  • Discuss how the genome and proteome contribute to the specialization of a cell

Key Points

  • Every cell within an organism shares the same genome (with exceptions, i.e. mature red blood cells), but has variation between its proteomes.
  • Gene expression involves the process of transcribing DNA into RNA and then translating RNA into proteins.
  • Gene expression is a highly complex and tightly-regulated process.

Key Terms

  • somatic: part of, or relating to the body of an organism
  • genome: the cell’s complete genetic information packaged as a double-stranded DNA molecule
  • proteome: the complete set of proteins encoded by a particular genome

Each somatic cell in the body generally contains the same DNA. A few exceptions include red blood cells, which contain no DNA in their mature state, and some immune system cells that rearrange their DNA while producing antibodies. In general, however, the genes that determine whether you have green eyes, brown hair, and how fast you metabolize food are the same in the cells in your eyes and your liver, even though these organs function quite differently. If each cell has the same DNA, how is it that cells or organs are different? Why do cells in the eye differ so dramatically from cells in the liver ?

Whereas each cell shares the same genome and DNA sequence, each cell does not turn on, or express, the same set of genes. Each cell type needs a different set of proteins to perform its function. Therefore, only a small subset of proteins is expressed in a cell that constitutes its proteome. For the proteins to be expressed, the DNA must be transcribed into RNA and the RNA must be translated into protein. In a given cell type, not all genes encoded in the DNA are transcribed into RNA or translated into protein because specific cells in our body have specific functions. Specialized proteins that make up the eye (iris, lens, and cornea) are only expressed in the eye, whereas the specialized proteins in the heart (pacemaker cells, heart muscle, and valves) are only expressed in the heart. At any given time, only a subset of all of the genes encoded by our DNA are expressed and translated into proteins. The expression of specific genes is a highly-regulated process with many levels and stages of control. This complexity ensures the proper expression in the proper cell at the proper time.

In this section, you will learn about the various methods of gene regulation and the mechanisms used to control gene expression, such as: epigenetic, transcriptional, post-transcriptional, translational, and post-translational controls in eukaryotic gene expression, and transcriptional control in prokaryotic gene expression.


Protein VP16

Transgenic overexpression of a constitutively active form of CREB (VP16-CREB) lowered the threshold for L-LTP. Gene expression analysis of this transgenic showed BDNF as a key molecule for the maintenance of LTP. However, excessive activation of CREB resulted in abnormalities, such as hippocampal neuronal loss and epileptic seizure, and thus L&M could not be assessed in this transgenic. On the other hand, viral overexpression of wild-type CREB was shown to enhance memory: viral expression in amygdala enhanced fear conditioning while expression in the hippocampus enhanced spatial memory.

The activity of CREB can be regulated by molecular interactions with other transcription regulators in the nucleus. In Aplysia, inhibiting a negative regulator of CREB, ApCREB2 was shown to lower the threshold for long-term synaptic plasticity. Recently, three different mice models show that manipulating CREB suppressors can also enhance synaptic plasticity and memory in mammalian brain. First, expression of a broad dominant-negative inhibitor (EGFP-AZIP) of the C/EBP family of transcription factors in mouse forebrain was found to suppress the repressor isoform of C/EBPβ and decrease the expression of the activating transcription factor 4 (ATF4). ATF4 is a negative regulator of CREB. Thus, EGFP-AZIP, by suppressing two different transcriptional repressors, shifts the balance toward transcriptional activators, in both the CREB and C/EBP families. Importantly, expression of EGFP-AZIP lowered the threshold for LTP and memory formation: a tetanus that induces only early stages of LTP (E-LTP) in controls can induce transcription-dependent later forms of LTP (L-LTP) in EGFP-AZIP mice. Behavioral analysis revealed enhanced learning in mutant mice trained with a weak protocol in the Morris water maze. Second, mice heterozygous for a point mutation that prevented phosphorylation of the eIF2α at serine 51 (eIF2α +/S51A ) showed decreased levels of ATF4 protein. Stimulation that induced E-LTP in controls was capable of inducing L-LTP in the eIF2α +/S51A mutants. Importantly, these mice showed improved L&M in a variety of behavioral tasks, including contextual and cued fear conditioning, conditioned taste aversion, and latent inhibition. Finally, deletion of GCN2, a conserved eIF2α kinase, reduced phosphorylation of eIF2α, subsequently suppressed the translation of ATF4 mRNA. Similar to the eIF2α +/S51A knock-in mutant, the threshold for L-LTP was lowered and spatial learning was enhanced in the GCN2 KO mice. These studies support the hypothesis that the transcriptional repressor ATF4 is an important negative regulator of synaptic plasticity and memory and suggest that translation may be an important regulatory node in plasticity and memory.

Overexpression of CaMKIV in mouse forebrain led to an increase in the levels of CREB activity and to larger LTP in both hippocampus and anterior cingulate cortex. Moreover, these transgenics showed enhanced contextual fear and social recognition memory. Interestingly, CaMKIV overexpression rescued age-related decline in fear conditioning. Taken together, these studies showed that enhancing CREB activity either by suppressing its negative regulators or by activating its positive regulators can enhance synaptic plasticity and memory.


Background

Alternative splicing (AS) is a widespread mechanism of gene regulation that generates multiple mRNA isoforms from a single gene, dramatically diversifying the transcriptome (and proteome) of eukaryotic cells. Ninety-five percent of multi-exonic mammalian genes undergo AS, producing mRNA isoforms which often differ in coding capacity, stability, or translational efficiency and that can be translated into proteins with distinct structural and functional properties [1, 2]. AS contributes to the regulation of many biological processes in multicellular eukaryotes, including embryonic development and tissue specification (reviewed in [3]). During the last decade, progress has been made to understand the role of post-transcriptional regulation (including AS) in the maintenance of cellular pluripotency and cell fate decisions, discovering genes differentially spliced between stem cells and differentiated cells and splicing regulators that control these choices [4,5,6,7,8,9,10,11].

During reprogramming into induced pluripotent stem (iPS) cells, somatic cells revert to a pluripotent state after overexpression of the transcription factors OCT4, SOX2, KLF4, and MYC (OSKM) [12]. Substantial progress has been made to understand the process at the transcriptional and epigenetic level, such as by identifying numerous roadblocks and some facilitators, but comparatively little is known about how post-transcriptional regulation impacts cell fate decisions. Recent work has revealed the functional relevance and conservation of splicing regulation during reprogramming [7, 13,14,15,16]. A conserved functional splicing program associated with pluripotency and repressed in differentiated cells by the RNA-binding proteins MBNL1 and MBNL2 was previously reported [7]. This splicing program includes a mutually exclusive exon event in the transcription factor FOXP1: a switch in inclusion of Foxp1 exons 16/16b modulates the functions of the transcription factor between pluripotent and differentiated cells [6]. Illustrating the complexity of such splicing program, dynamic changes of AS during cell reprogramming of mouse embryonic fibroblasts (MEFs) revealed sequential waves of exon inclusion and skipping in reprogramming intermediates and the functional role of splicing regulators in modulating reprogramming, in particular during the initial mesenchymal-to-epithelial transition (MET) phase [17]. Given the limited efficiency of cell reprogramming in this system, subpopulations of reprogramming intermediates had to be isolated through the expression of a pluripotency marker, biasing studies to the most prevalent and dominant factors.

Here we took advantage of the rapid, highly efficient and largely synchronous reprogramming of pre-B cells (hereafter referred to as “B cell reprogramming”), obtained by a pulse of the transcription factor C/EBPα followed by induced OSKM expression [18, 19] to study the dynamics of AS during this transition. The essentially homogeneous reprogramming of the cells in this system allowed detailed temporal transcriptome analyses of the bulk population, without the need of selecting for reprogramming intermediates. We established clusters of temporal regulation and compared these changes with the ones differentially spliced in MEF reprogramming [17]. Analyzing the dynamic expression of RNA-binding proteins (RBPs) during reprogramming, we inferred potential AS regulators, of which three were studied in detail. Characterization of these factors, namely CPSF3, hnRNP UL1, and TIA1, by perturbation experiments demonstrated their role as AS regulators in the induction of pluripotency.


Materials and Methods

Primary B Cell Isolation and Culture.

Spleens were isolated from 8- to 10-week-old C57BL˶J mice (The Jackson Laboratory). Splenic T cells were removed by incubating with monoclonal anti-Thy1.2 IgM (Sigma) followed by lysis with rabbit complement (Cedarlane Laboratories). At this step, the cells were typically 95% pure B220 + B cells by FACS analysis. To obtain highly pure naïve B cells for microarray studies, these cells were stained with a biotin-conjugated anti-CD43 antibody (PharMingen) followed by streptavidin-conjugated magnetic microbeads (Miltenyi Biotec, Auburn, CA) and passed through a depletion-type magnetic sorting column (Miltenyi Biotec). Unbound cells were collected as the purified resting B cell sample—over 98% pure B220 + B cells expressing low levels of activation markers such as ICAM-1, CD23, and B7.2 by FACS analysis (data not shown). B cells were cultured in RPMI media 1640 supplemented with 10% FBS, 50 μM β-mercaptoethanol, and 1% penicillin/streptomycin (Life Technologies, Rockville, MD) at 37ଌ under 10% CO2. Cells were stimulated with soluble CD8�L fusion at 300 ng/ml or lipopolysaccharide at 20 μg/ml unless otherwise indicated. Cells stimulated for microarray analysis were cultured at 2.5 × 10 6 cells/ml.

Measurement of Cellular Proliferation and Apoptosis.

For proliferation assays, B cells were stimulated at 5.0 × 10 5 cells/ml in 96-well plates for 42 h, pulsed with 0.5 㯌i 3 H-thymidine per well, incubated for an additional 6 h, and collected on a 96-well filtermat by using an automated harvester. Activity was measured in a 96-well format on a scintillation counter. Cell death was measured through FACS analysis after 24 h of culture by double staining with propidium iodide and FITC-conjugated anti-Annexin V antibody. The percentage of cells in the double-negative quadrant was recorded as the viable fraction.

Target Preparation and Microarray Analysis.

Primary B cells were flash frozen in liquid nitrogen after stimulation for 2 h with or without soluble CD40L in the presence of DMSO (0.1%), U0126 (10 μM), SB203580 (10 μM), or LY294002 (10 μM), or for variable lengths of time in the presence of CD40L (300 ng/ml) alone or lipopolysaccharide (20 μg/ml) alone or in media. Total and poly(A) + RNA were isolated by using commercially available kits (Qiagen, Chatsworth, CA) with a typical yield of 5� μg total and 0.5𠄱.0 μg of poly(A) + RNA per condition. Synthesis of cDNA was carried out by using a T7-oligo-dT primer (Gensent, La Jolla, CA) with Superscript-II RT and related reagents (GIBCO). In vitro transcription of biotin-labeled cRNA was carried out by using a commercially available kit (Enzo Diagnostics). Yield of cRNA typically ranged from 40 to 80 μg per condition.

Mu6500 expression probe arrays (Affymetrix) were used for expression screening. Hybridization was carried out at 45ଌ for 16 h under constant rotation. After washing and staining, chips were scanned by using an argon–ion laser scanner (Hewlett–Packard) at a wavelength of 570 nM. Gene expression results were captured, normalized through global scaling, and analyzed by using genechip analysis software (Affymetrix).

Hierarchical Clustering.

Determination of gene induction, inhibition, and pathway dependence was based on multiple genechip parameters, including fold change and average difference change, as explained in detail in the supporting information on the PNAS web site, www.pnas.org. Hierarchical clustering was performed by using publicly available software (http://rana.stanford.edu/software/). Single-axis clustering of average difference change values (Fig. ​ (Fig.2) 2 ) and bidirectional clustering of pathway dependence profiles (Fig. ​ (Fig.3) 3 ) were performed through average linkage clustering by using an uncentered Pearson's correlation coefficient as the similarity metric.

CD40-specific genes include numerous mediators of lymphoid trafficking and communication. (A) Hierarchical clustering was performed to distinguish stimulus-specific gene clusters. Shown are representative early (Top) and middle and late (Bottom) CD40-specific clusters. (B) Examples of CD40-specific genes with potential roles in immune cell trafficking and communication.

Differential requirements for various CD40-activated signaling pathways in gene induction and inhibition. Dependence of gene induction/inhibition on multiple pathways and on new protein synthesis (CHX) was determined as described in Materials and Methods, and the results were hierarchically clustered. Inhibited pathways: p50−/−:c-Rel−/−:p65−/+ (㮫 2.5-KO), ERK (U0126), p38 (SB203580), and PI-3K (LY294002). Closeups of representative clusters of (A) induced and (B) inhibited genes are shown. Gold squares represent genes whose induction/inhibition by CD40L is independent of a given pathway (e.g., not blocked by addition of drug). Blue squares represent genes that depend on a given pathway, and black squares represent genes that did not meet criteria for classification as either independent or dependent.


Materials and methods

Cloning

The 120 bp IE from the hamster Aprt gene [21] was inserted as a dimer bounded by two lox elements into an engineered PacI restriction site 40 bp upstream to the human γ A -globin gene transcription start site ( Figure 5 ). The HindIII/XhaI fragment was then cloned into the yeast integrative plasmid pRS306 that was then inserted by homologous recombination into the human β-globin YAC-harboring yeast cells A201F4.3 [18]. Colonies were subsequently screened for growth on plates lacking uracil. Correct integration was verified by Southern blot analysis. Plasmid sequences were removed by induction of “looping out” through growth on 5FOA and correct excision was verified by Southern blot analysis.

We made transgenic embryos (12.5 dpc) using either a plasmid that contains the normal promoter of the human γ A -globin gene (-IE), or a plasmid that contains the promoter of the human γ A -globin gene modified to harbor a dimer of the IE bounded by two lox elements (ʲIE) 40 bp upstream to the γ A transcription start site, and tested total founder embryonic DNA for methylation at specific restriction sites by southern blot analysis. This plasmid (ʲIE) was later used as a template for homologous recombination in the YAC (see methods).

The map indicates the restriction site locations according to PubMed accession number NG_00007.

Bold marked restriction enzymes are methylation sensitive. Total founder embryo DNA was digested with HindIII alone or together with CfoI, or alternatively with StuI/XbaI alone or together with HpaII, MspI or AvaI.

Southern-blot analysis was performed using probes 5′ or 3′ as labeled.

The sizes of expected bands are indicated on the autoradiogram. Data shown are representative of results obtained with several transgenic founder mice for each construct.

From this experiment, we conclude that a double IE is capable of inducing undermethylation over a distance of at least 500 bp in each direction.

Transgenic mice and methylation analysis

YAC DNA was purified from pulse-field gels according to standard protocols [44] and injected into fertilized mouse eggs that were transferred to foster mothers. Littermates were screened for the β-globin YAC transgene by PCR, and positive samples verified by Southern blot. All three transgenes (lines 47, 64, 113) used for analysis were found to be completely intact and present as a single copy. Founders were crossed with Cre [19] or Mx-Cre mice [20]. To remove the IE sequences after birth Mx-Cre X β-globin YAC F1 mice were injected 4 times with polyI-polyC (Sigma) on alternate days. MEFs (passage number 3𠄴) carrying a methylated γ A gene were prepared from Cre embryos. MEFs carrying an unmethylated γ A gene were prepared from Mx Cre mice and then transfected with a type 5-cytomegalovirus Cre vector [45] to remove the IE element. Methylation patterns in non erythroid cells were analyzed either by Southern blot or bisulfite methylation analysis as described [46]. Following treatment, the DNA was amplified using the PCR primers forward -1 (5′-TTGTTTGAAAGGGTTTTTGGTTAAATTTTATTT-3′) and reverse-1 (5′-TCCTAATCACCAAAACCTACCTTCCCAAAA-3′) and subsequently with the nested primers forward -2 (5′-TTTTGGTTAAATTTTATTTATGGGTTGGTTAGTT-3′) and reverse-2 (5′-AACTTATAATAATAACCTTATCCTCCTCTATAAAATA-3′). The resulting products were cloned using the pGEM-T Easy Vector System I kit (Promega) and individual colonies then sequenced. Methylation patterns in purified erythroid cells were analyzed by digestion with methylation sensitive restriction enzyme followed by amplification by PCR.

Semiquantitative RT-PCR

Erythroblasts from fetal liver and adult spleen of Cre or Mx-cre crossed transgenic mice were isolated by MACS (Magnetic Activated Cell Sorter) with biotinilated α-ter119 antibodies (PharMingen). Mouse embryonic fibroblasts (MEFs) were derived from Cre or Mx-cre crossed 12.5 dpc transgenic embryos. RNA was extracted with TriPure Isolation reagent (Roche), treated (250 ng) with DNaseI (Promega) and converted to cDNA using the Molony murine leukemia virus reverse transcriptase (Promega) and random hexanucleotide pd(N)6 primers (Pharmacia) in a reaction volume of 50 µl under conditions recommended by the manufacturer. 1 or 3 µl of the cDNA was used for PCR reactions (95ଌ for 1 min, 58ଌ for 1 min, 72ଌ for 1 min) in the presence of 32 P𻇜TP (Amersham) using appropriate primer pairs [47]. These primers were designed to span intron-exon junctions in order to distinguish between cDNA and genomic DNA. RT-PCR fragments were separated on 5% or 7% polyacrylamide gels and exposed for autoradiography. The relative amount of γ A and γ G cDNA was defined by digestion with the restriction enzyme PstI that cuts only the γ A PCR product. The level of γ and β-globin transcription was measured by phosphor-imager analysis of diluted samples after normalizing for Aprt.

Chromatin Immunoprecipitation (ChIP)

Nuclei were prepared from cell culture or purified mouse spleen erythroblasts, treated with an HDAC inhibitor (PMSF) and digested by MNase (micrococcal nuclease) to generate mono-nucleosomes that were separated on a sucrose gradient [48]. Immunoprecipitation (IP) was carried out using anti-acetylated histone H4 or anti me-H3(Lys4) antibodies (Upstate Biotechnologies), and the bound fraction purified by protein A-Sepharose chromatography (Sigma). Input and Bound DNA fractions were analyzed by semiquantitative PCR using two concentrations. Primer sequences are available upon request.

In vivo footprinting

In vivo Dimethyl Sulfate (DMS) footprinting and ligation-mediated PCR (LMPCR) was performed as described earlier [49], [50], except that the in vivo DMS treatment was done on erythroid cells in cell suspension. In a 50 ml conical tube, 10� million cells were suspended in 10 ml of culture medium without bovine serum. DMS was added to a final concentration of 0.2%, and the cells were incubated at room temperature for 5 min. 40 ml of ice-cold PBS was added to stop the DMS reaction and the cells were centrifuged quickly (250 g, 3 min), washed two times with 30 ml of ice-cold PBS before DNA preparation. For the LMPCR experiment we designed the first primers in such way that they distinguished between the γ G and lox-P inserted γ A promoters. Primer extension was then carried out with either L1n: 5′-GCGTCTGGACTAGGAGCTTTTAAT-3′ or L1: 5′-AAGTAACGCATTTGCT GGAAG-3′ (which includes the IE element). Primer, L2: 5′-TTAATCTCAGACGTTCCAGAAGCGAGTGTG-3′ and LP25 linker primer were used for amplification. The run off hybridization probe was made on PCR fragment L3: 5′-CAGAAGCGAGTGTGTGGAACTGCTGAA-3′ – U: 5′-AAAAAAATTAAGCAGCAGTATCCTCTTGGG-3′ with the L3 primer.


Affiliations

Department of Chemistry, University of California, Riverside, Riverside, CA, USA

Lin Li, Preston Williams, Michelle Y. Wang, Zi Gao, Weili Miao & Yinsheng Wang

Department of Biochemistry, University of California, Riverside, Riverside, CA, USA

Environmental Toxicology Graduate Program, University of California, Riverside, Riverside, CA, USA

Ming Huang & Yinsheng Wang

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Contributions

L.L. and Y.W. conceived the project. P.W., W.M. and M.H. performed the G-quadruplex pull-down experiments and analyzed the mass spectrometry data. L.L., M.Y.W., Z.G. and W.M. performed the plasmid construction and cell culture experiments. L.L. and Z.G. performed the in vitro binding assay. L.L. performed the ChIP–seq, HiChIP–seq, RNA-seq and relevant data analysis. W.R. and J.S. assisted with the protein expression and purification. L.L. and P.W. analyzed the data. L.L. and Y.W. wrote the manuscript, which was reviewed and commented by all co-authors.

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For more information about gene regulation:

The National Human Genome Research Institute provides a definition of gene regulation in their Talking Glossary of Genetic Terms.

The Genetic Science Learning Center at the University of Utah offers an explanation of gene expression as it relates to disease risk.

Additional information about gene expression is available from yourgenome.org, a service of the Wellcome Trust.

The Khan Academy has an educational unit on gene regulation, including videos about gene regulation in bacteria and eukaryotes.


Synthetic biology in various cellular and molecular fields: applications, limitations, and perspective

Synthetic biology breakthroughs have facilitated genetic circuit engineering to program cells through novel biological functions, dynamic gene expressions, as well as logic controls. SynBio can also participate in the rapid development of new treatments required for the human lifestyle. Moreover, these technologies are applied in the development of innovative therapeutic, diagnostic, as well as discovery-related methods within a wide range of cellular and molecular applications. In the present review study, SynBio applications in various cellular and molecular fields such as novel strategies for cancer therapy, biosensing, metabolic engineering, protein engineering, and tissue engineering were highlighted and summarized. The major safety and regulatory concerns about synthetic biology will be the environmental release, legal concerns, and risks of the engineered organisms. The final sections focused on limitations to SynBio.


Acknowledgements

HEK293T p300 knockout cells were provided by X. Li. We thank S. Khochbin for brainstorming and critical reading of this manuscript. We thank K. Delaney and all other members of the Zhao and Becker laboratories for discussions and technical support. This work was supported by the University of Chicago, Nancy and Leonard Florsheim family fund (Y.Z.), NIH grants R01GM115961, R01DK118266 (Y.Z.), R01DK102960, R01HL137998 (L.B.), R01CA129325, R01DK071900 (R.G.R.), and NSF1808087 (Y.G.Z.).


Supplementary boxes 1 and 2

The forced expression of a particular gene in a cell type in which the gene is usually not expressed at a desired level.

The persistent production of a target protein by any cell that contains the encoding gene.

Any natural or synthetic system (for example, a promoter, an RNA molecule or a signalling pathway) that allows initiation, interruption or termination of target gene expression.

Chimeric regulatory proteins consisting of a trafficking domain (controls translocation to target DNA, RNA or protein destination) and a regulatory domain (specifies target-specific activity).

Carriers of coding genes that are not part of the endogenous chromosome, such as plasmid DNA, mini-circles or replicon RNA.

(gRNAs). Synthetic RNA molecules that bind and guide a specific Cas protein (CRISPR-associated protein) towards a gRNA-specific DNA or RNA target sequence through complementary base pairing also known as single-guide RNAs (sgRNAs).

A single-stranded RNA or DNA sequence forming a secondary structure that undergoes a considerable conformational change upon binding to a specific chemical ligand (small molecules, ions or proteins) with high affinity.

Mutually orthogonal trans-regulators

A set of trans-regulators operating at parallel genetic targets that do not show cross-interaction in terms of direct binding or potential influence on each other’s downstream targets.

Regulatory segments within an mRNA that bind to specific metabolites and modify the expression of the protein product of the riboswitch-containing mRNAs.

Products of a chimeric fusion between an aptamer and a (self-cleaving) ribozyme in which the ligand-dependent conformational change of the aptamer is also propagated to affect the activity of the ribozyme.

Proteins in which an active or inactive conformation is reversibly triggered by ligand binding or other stimuli (such as light).

(CRY2). A protein derived from Arabidopsis thaliana that undergoes reversible oligomerization or heterodimerization with CIBN (amino-terminal domain of cryptochrome-interacting basic helix–loop–helix) upon exposure to blue light.

A type I topoisomerase from bacteriophage P1 that catalyses site-specific recombination (inversion or deletion) of DNA between loxP sites

Transient memory devices with a finite capacity for storing cellular information that ensure unperturbed functionality of a regulated subsystem when sufficiently charged.

Non-homologous end joining

(NHEJ). An error-prone endogenous DNA repair mechanism for double-stranded breaks that is usually initiated when a correct DNA template is not provided.

Synthetic (bio)computing devices that convert multiple input signals into a smaller number of outputs according to a defined logic algorithm.

A cell–cell communication mechanism evolved in many bacterial species that allows specific (sub)populations to measure their local density (by production, release, accumulation and detection of a signalling molecule) and subsequently coordinate gene expression.

A protein motif that is irreversibly excised from a larger protein structure when specific peptide domains are brought into close proximity.

A type of resettable memory of living cells that is based on inheritable post-translational protein modifications and DNA conformations rather than a change in nucleotide sequences.

Delivery of foreign gene elements into host cells through episomal vectors that do not permanently integrate into the genome and therefore reside in the cells for only a few rounds of cell division.

Simplified replicates of biological targets created outside of their natural environment that retain all basic molecular functionalities important for (high-throughput) drug screening and development.

Biological targets that should not be activated by a potential drug candidate.

Sessile communities of virulent bacteria encased in an extracellular matrix adhering to a solid surface and showing increased survival compared with free-floating bacteria.

Systems that enable biased inheritance of a genetic element so that offspring within a population have a >50% chance of inheritance of a given trait.

Medical complications related to the immunological adverse effects in a patient (host) caused by implanted or infused therapeutics (graft).

An adipocyte-derived protein hormone that increases insulin sensitivity in target tissues, such as fat, muscle or liver.

An autoimmune disorder characterized by hyperthyroidism in which autoantibodies constitutively trigger thyroid hormone production from the thyroid gland.