Terms Of Cell Density Research Articles

Inter and intra-specific growth and domoic acid production in relation to nutrient ratios and concentrations in Pseudo-nitzschia: phosphate an important factor

The factors responsible for inducing the synthesis of toxins and responses from toxic phytoplankton blooms remain unclear. In this study we compare the influence of genotypic (at both the intra and interspecific levels) and environmental factors (nutrient concentration and ratio) on growth (in terms of cell densities) and domoic acid (DA) production in three Pseudo-nitzschia species: P. australis, P.pungens and P.fradulenta. A strong phosphate effect was detected. More precisely, a low initial concentration in phosphate, even at high initial nitrogen and silicate concentrations, induced the highest DA concentrations and the lowest cell densities in all strains/species studied. In contrast, a low initial concentration of nitrogen and silicate combined, with a higher phosphate concentration resulted in low cell densities, but without high DA production. Inter-species effects were also observed in DA production, where P. australis represented the most toxigenic species of all. Intra-specific variations were only moderate, except for a recently isolated P. australis strain, suggesting the influence of time since isolation on the physiology and DA production of Pseudo-nitzschia species. Overall, the lack of strong interaction between environmental and genotypic factors showed that the various genotypes investigated did not extensively diverge in their ability to respond (in terms of DA production and cell densities) to contrasting nutrient supply.

Regulation of membrane fixation and energy production/conversion for adaptation and recovery of ZnO nanoparticle impacted Nitrosomonas europaea.

The ZnO nanoparticle (NP) effects on typical ammonia-oxidizing bacteria, Nitrosomonas europaea in a chemostat bioreactor, and the cells' toxicity adaptation and recovery potentials were explored. Hardly any inhibition was observed when the NP concentration was high up to 10mg/L. The cells exposed to 50mg/L ZnO NPs displayed time-dependent impairment and recovery potentials in terms of cell density, membrane integrity, nitrite production rate, and ammonia monooxygenase activity. The 6-h NP stress impaired cells were nearly completely restored during a 12-h recovery incubation, while the longer exposure time would cause irretrievable cell damage. Microarray analysis further indicated the transcriptional adaptation of N. europaea to NP stress. The regulations of genes encoding for membrane permeability or osmoprotectant, membrane integrity preservation, and inorganic ion transport during NP exposure and cell recovery revealed the importance of membrane fixation and the associated metabolisms for cells' self-protection and the following recovery from NP stress. The oxidative phosphorylation, carbon assimilation, and tricarboxylic acid (TCA) cycling pathways involved in the cells' antitoxicity activities and would promote the energy production/conversion efficiency for cell recovery. The heavy metal resistance, histidine metabolism, toxin-antitoxin defense, glycolysis, and sulfate reduction pathways were also suggested to participate in the cell detoxication and recovery processes. All these findings provided valuable insights into the mechanisms of cell-mediated ZnO NP cytotoxicity and their potential impacts on wastewater nitrogen removal system.

Rapid Neuronal Differentiation of Induced Pluripotent Stem Cells for Measuring Network Activity on Micro-electrode Arrays.

Neurons derived from human induced Pluripotent Stem Cells (hiPSCs) provide a promising new tool for studying neurological disorders. In the past decade, many protocols for differentiating hiPSCs into neurons have been developed. However, these protocols are often slow with high variability, low reproducibility, and low efficiency. In addition, the neurons obtained with these protocols are often immature and lack adequate functional activity both at the single-cell and network levels unless the neurons are cultured for several months. Partially due to these limitations, the functional properties of hiPSC-derived neuronal networks are still not well characterized. Here, we adapt a recently published protocol that describes production of human neurons from hiPSCs by forced expression of the transcription factor neurogenin-212. This protocol is rapid (yielding mature neurons within 3 weeks) and efficient, with nearly 100% conversion efficiency of transduced cells (>95% of DAPI-positive cells are MAP2 positive). Furthermore, the protocol yields a homogeneous population of excitatory neurons that would allow the investigation of cell-type specific contributions to neurological disorders. We modified the original protocol by generating stably transduced hiPSC cells, giving us explicit control over the total number of neurons. These cells are then used to generate hiPSC-derived neuronal networks on micro-electrode arrays. In this way, the spontaneous electrophysiological activity of hiPSC-derived neuronal networks can be measured and characterized, while retaining interexperimental consistency in terms of cell density. The presented protocol is broadly applicable, especially for mechanistic and pharmacological studies on human neuronal networks.

Rapid Neuronal Differentiation of Induced Pluripotent Stem Cells for Measuring Network Activity on Micro-electrode Arrays

Neurons derived from human induced Pluripotent Stem Cells (hiPSCs) provide a promising new tool for studying neurological disorders. In the past decade, many protocols for differentiating hiPSCs into neurons have been developed. However, these protocols are often slow with high variability, low reproducibility, and low efficiency. In addition, the neurons obtained with these protocols are often immature and lack adequate functional activity both at the single-cell and network levels unless the neurons are cultured for several months. Partially due to these limitations, the functional properties of hiPSC-derived neuronal networks are still not well characterized. Here, we adapt a recently published protocol that describes production of human neurons from hiPSCs by forced expression of the transcription factor neurogenin-212. This protocol is rapid (yielding mature neurons within 3 weeks) and efficient, with nearly 100% conversion efficiency of transduced cells (>95% of DAPI-positive cells are MAP2 positive). Furthermore, the protocol yields a homogeneous population of excitatory neurons that would allow the investigation of cell-type specific contributions to neurological disorders. We modified the original protocol by generating stably transduced hiPSC cells, giving us explicit control over the total number of neurons. These cells are then used to generate hiPSC-derived neuronal networks on micro-electrode arrays. In this way, the spontaneous electrophysiological activity of hiPSC-derived neuronal networks can be measured and characterized, while retaining interexperimental consistency in terms of cell density. The presented protocol is broadly applicable, especially for mechanistic and pharmacological studies on human neuronal networks.

The Growth Behavior of Chlorella vulgaris in Bisphenol a under different Cultural Conditions

The effects of different initial concentrations of bisphenol A (BPA) on Chlorella vulgaris and removal capacity of BPA by Chlorella vulgaris were investigated under the light and the dark cultural conditions. Experiments were performed in 250 mL flasks under light and dark conditions with different BPA concentrations. Results showed that 0-20 mg·L-1 BPA concentration under the light condition and 0-10 mg·L-1 BPA concentration under dark condition plays a promoting role on the growth of Chlorella vulgaris in terms of cell density. The effect of BPA removal under light condition was obviously better than that under the dark condition. The maximum BPA removal rates were 3.425 ± 0.145 mg (L·d)-1 and 1.530 ± 0.025 mg (L·d)-1 under two conditions and were observed during 2-4 d and 0-2 d, respectively. The largest removal amounts of BPA under two conditions were all investigated in L-BPA50 and D-BPA50 groups. Both superoxide dismutase (SOD) and catalase (CAT) activities were promoted in all the treatments, which proved that C. vulgaris showed a positive response to the BPA stress condition. SOD activity showed sensitive and responsive to the new medium since it was promoted immediately on the incubation day. CAT activity was supposed to be more tightly controlled in response to BPA because its level was related to the BPA removal.

Inhibition effect of engineered silver nanoparticles to bloom forming cyanobacteria

Silver nanoparticle (AgNP) has a wide range antibacterial effect and is extensively used in different aspects of medicine, food storage, household products, disinfectants, biomonitoring and environmental remediation etc. In the present study, we examined the growth inhibition effect of engineered silver nanoparticles against bloom forming cyanobacterial M. aeruginosa strain. AgNPs were synthesized by a chemical reduction method at room temperature and UV–Vis spectroscopy, scanning electron microscopy (SEM), transmission electron microscope (TEM) showed that they presented a maximum absorption at 410 nm and size range between 10 and 18 nm. M. aeruginosa cells exposed during 10 d to AgNPs to a range of concentrations from 0 to 1 mg l−1. The changes in cell density and morphology were used to measure the responses of the M. aeruginosa to AgNPs. The control and treatment units had a significant difference in terms of cell density and growth inhibition (p < 0.05). Increasing the concentration of AgNPs, a reduction of the cell growths in all treatment was observed. The inhibition efficiency was reached 98.7% at higher concentration of AgNPs nanoparticles. The term half maximal effective concentration (EC50) based on the cell growth measured by absorbance at 680 nm (A680) was 0.0075 mg l−1. The inhibition efficiency was 98.7% at high concentration of AgNPs (1 mg l−1). Image of SEM and TEM reflected a shrunk and damaged cell wall indicating toxicity of silver nanoparticles toward M. aeruginosa.

An improved microtiter plate assay to monitor the oxidative burst in monocot and dicot plant cell suspension cultures.

BackgroundA screening method for elicitor and priming agents does not only allow detecting new bioactive substances, it can also be used to understand structure–function relationships of known agents by testing different derivatives of them. This can not only provide new lead compounds for the development of novel, more environment-benign, bio-based agro-chemicals, it may eventually also lead to a better understanding of defense mechanisms in plants. Reactive oxygen species (ROS) are sensitive indicators of these mechanisms but current assay formats are not suitable for multiplex screening, in particularly not in the case of monocot systems.ResultsHere we describe continuous monitoring of ROS in 96-well microtiter plates using the chemiluminescent probe L012, a luminol derivative producing chemiluminescence when oxidised by ROS like hydrogen peroxide, superoxide, or hydroxyl radical that can thus be used as an indicator for these ROS. We were able to measure ROS in both monocot (Oryza sativa) and dicot (Medicago truncatula) cell suspension cultures and record dose dependencies for the carbohydrate elicitors and priming agents ulvan and chitosan at low substrate concentrations (0.3–2.5 µg/ml). The method was optimized in terms of cell density, L012 concentration, and pre-incubation time. In contrast to the single peak observed using a cuvette luminometer, the improved method revealed a double burst in both cell systems during the 90-min measuring period, probably due to the detection of multiple ROS rather than only H2O2.ConclusionWe provide a medium throughput screening method for monocot and dicot suspension-cultured cells that enables direct comparison of monocot and dicot plant systems regarding their reaction to different signaling molecules.Electronic supplementary materialThe online version of this article (doi:10.1186/s13007-016-0110-1) contains supplementary material, which is available to authorized users.

Neuroplasticity Changes of Rat Brain by Musical Stimuli during Fetal Period.

Fetal development of the central nervous system is an important and sensitive stage which is affected by many external and internal stimuli. This study aimed to investigate effect of musical stimuli on fetal rat brain. In this experimental study, twelve female Wistar rats were selected and evenly assigned to control and musical groups. The females were mated with a male rat of the same genotype. Musical group was exposed to classic music with 60 dB power for 90 minutes twice per day from 2(nd) to 20(th) day of gestation. The control rats were handled similar to the musical group, but were not exposed to music. Before parturition, all the dams were anesthetized, and their blood samples were obtained and used for corticosterone (COS) measurement. They were transcardially perfused by electron microscope (EM) fixative agent. The fetal brains were extracted intact and used for slice preparation. Horizontal slices were made for electron microscope preparation, and images were taken and analyzed in terms of cell density and morphological changes. EM observation indicated significant morphological difference in cellular and intercellular spaces between the two groups. Music-treated fetuses had significantly higher cell density in parietal cortex and music-treated dams had lower COS level. It was concluded that prenatal music would have a great impact on neuroplasticity of fetal rat brain, at least indirectly. Although the rat fetuses cannot hear until birth, music-induced reduction in COS blood level of dams might be the reason for neuroplasticity of fetal brain.

Age- and degeneration-related variations in cell density and glycosaminoglycan content in the human cervical intervertebral disc and its endplates.

The first aim of this study was to quantify cell density in cervical intervertebral discs (IVDs) and endplates of varying age and degeneration grade. The second aim was to analyze glycosaminoglycan (GAG) content in cervical IVDs and their endplates. Sixty cervical IVDs were excised from 30 human cadavers, not later than 24 hours post-mortem. Each sample underwent sectioning. Half of each sample underwent GAG content analysis using the dimethylmethylene blue binding assay. The other half underwent histological processing, histological degeneration grading, and cell density assessment using the Abercrombie method. The nucleus pulposus (NP) (4218 ± 417 cells/mm³) had significantly higher cell density than the anterior annulus fibrosus (AF) (3283 ± 438 cells/mm³; p < 0.0001), and similar cell density (4464 ± 551 cells/mm³; p = 0.36) to the posterior AF. Cell density was similar throughout the different regions of the endplate. The NP (619 ± 178 µg/mg dry weight) had a significantly higher GAG content than both the anterior (428 ± 199 µg/mg dry weight; p < 0.0001) and posterior AF (524 ± 218 µg/mg dry weight; p < 0.0001). In conclusion, this study introduces detailed 3D maps of cervical IVD and endplate cell density and GAG content. Furthermore, it shows that cervical IVDs and their endplates only slightly differ, in terms of cell density and GAG content, from lumbar IVDs.

Responses of Planktothrix agardhii and Pseudokirchneriella subcapitata to Copper Sulfate (CuSO4 · 5H2O) and a Chelated Copper Compound (Cutrine®-Ultra)

Reliable viability measures are needed to predict responses of algae to phytotoxic exposures. Non-axenic laboratory cultures of Planktothrix agardhii and Pseudokirchneriella subcapitata were exposed to a series of concentrations of CuSO4 · 5H2O (0.1–0.5 and 1.0–8.0 mg Cu/L) and a chelated copper compound with an adjuvant, Cutrine®-Ultra (0.05–0.25 and 1.0–8.0 mg Cu/L) in 7-day static laboratory experiments. Algal viability measures in terms of cell density, uptake of mortal stain (erythrosin b), chlorophyll a concentration, pheophytin a concentration, and respiration (measured as 2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyl tetrazolium formazan absorbance (INT)) were discerned daily. The time and concentration required to achieve algal control, 96-h EC50s, potency slopes, and doubling times were calculated from algal responses if algal viability measures were accurate and precise. Cell densities and erythrosin b-stained cells had sufficient accuracy and precision to differentiate responses of P. agardhii and P. subcapitata from resident algae while chlorophyll a concentrations and INT formazan absorbances did not discriminate. In this study, pheophytin a concentrations lack precision and accuracy. P. agardhii was an order of magnitude more sensitive than P. subcapitata, and Cutrine®-Ultra was more than twice as potent as CuSO4 · 5H2O. This laboratory study corroborates previous laboratory and field studies suggesting that chelated copper-based algaecides when applied in the field can selectively control specific target algae at a lower copper concentration than CuSO4 · 5H2O. Individual algal viability measures such as cell density and erythrosin b staining can measure the relevant change in algal assemblage as a result of exposure.

Biofouling on microfiltration membranes in MBRs: Role of membrane type and microbial community

Cross-flow filtration experiments were performed using three model biofoulants with increasing complexity: a monospecies assay using Pseudomonas aeruginosa or Escherichia coli, a duospecies assay using both microorganisms, and finally a multispecies assay using activated sludge spiked with P. aeruginosa. Three different microfiltration membranes were tested: polyvinyldifluoride, polyethylene and polysulfone. The biofouling was characterized in terms of cell density, community composition and relative permeability decrease caused by the different biofoulants. The data show that a good biofilm pioneer, like P. aeruginosa, was able to bind to any kind of membrane. However, when activated sludge spiked with P. aeruginosa was used, an enhanced biofouling behavior by the activated sludge members was found on the polyvinyldifluoride membrane. This paper highlights the importance of the kind of species, the microbial interactions and the community composition during the biofouling development.

Comparison of two sampling methods when studying periphyton colonization in Lam Tsuen River, Hong Kong, China

We used standard periphyton samplers to examine the colonization pattern of periphytic algae on artificial substrates (glass slides) in Lam Tsuen River, Hong Kong, in dry (winter) and wet (summer) seasons. In each season, six replicated slides were retrieved randomly and replaced by new slides at weekly intervals over a period of 6 weeks. We thus obtained two batches of slides, both with a series of different exposure times (1 to 6 weeks): one batch was set up at the same time (start of the sampling) and the other was harvested at the same time (end of the sampling). Changes in taxonomic composition, species diversity (Shannon-Wiener diversity index), standing crop (in terms of cell density and cell biovolume), and abundance of the abundant algal species were monitored and compared between the two batches of slides. The succession patterns of the periphytic algae were similar between the two batches in each season, while more remarkable differences were observed between the two seasons, suggesting that either batch would be suitable for a colonization study of periphytic algae. The cell density was dominated by diatoms in both seasons, while the cell biovolume was dominated by diatoms in winter and by green algae in summer. The cell density and biovolume attributed to blue green algae was relatively small. Most of the diatom species exhibited similar colonization patterns throughout the experiment, while green algae showed different succession patterns in different seasons or sampling methods, indicating that diatoms are better bio-indicators than green algae for a periphyton colonization study. In general, the diversity indices and the standing crops reached their maximums at around week 4, and they were higher in summer than in winter.

Results of Confocal Microscopy Examinations after Collagen Cross-Linking with Riboflavin and UVA Light in Patients with Progressive Keratoconus

Purpose: Keratoconus is a predominantly bilateral form of corneal degeneration that is associated with central thinning and cone-shaped bulging of the cornea usually accompanied by a progressive reduction in visual acuity. A recent therapeutic option is cross-linking, a procedure designed to prevent the progression of keratoconus by the photochemical cross-linkage of collagen fibers. Patients and Methods: Eight eyes in 8 patients with progressive keratoconus were treated by the photochemical cross-linking method using riboflavin and UVA light. In addition to the usual ophthalmological examinations, patients were examined pre- and postoperatively by confocal in vivo laser scanning microscopy. Follow-up examinations were performed at 2 weeks and at 2, 4, 6 and 12 months postoperatively. Results: Complete regeneration of corneal epithelium was detected by 2 weeks after therapy at the latest. The sub-basal nerve plexus could not be visualized by confocal microscopy after treatment. Immediately after treatment, the anterior corneal stroma had a honeycombed appearance but without the typical hyperreflective keratocyte nuclei. At about 6 months postoperatively, the corneal stroma had virtually regained its normal configuration. After therapy, confocal microscopy revealed that corneal endothelium was normal in terms of cell density and morphology at every time point. Conclusions: Confocal in vivo laser scanning microscopy is an investigative technique that permits reproducible visualization of structural changes in the cornea (epithelium, stroma and endothelium) following collagen cross-linking with riboflavin and UVA light. Once epithelial healing is complete, the epithelium and endothelium appear to be unaffected by the treatment. The most noteworthy structural changes, which are detected on confocal microscopy shortly after treatment, involve the anterior and middle corneal stroma. Over the course of time, up to 12 months postoperatively, these changes show a definite tendency to regress.

Effects of heat treatment and concentration of fish serum on cell growth in adhesion culture of Chinese hamster ovary cells

The effects of heat treatment and concentration of fish serum (FS) on cell growth and human granulocyte-macrophage colony-stimulating factor (hGM-CSF) production in an adhesion culture of recombinant Chinese hamster ovary (CHO) cells, DR1000L4N, were investigated. The addition of heat treated FS instead of non-heat-treated FS improved cell growth in terms of cell density, which reached 60% that in 10% fetal calf serum (FCS)-containing medium (FCS medium). A decrease in FS concentration from 10 to 1.25% markedly increased cell density, which was 79% that in 10% FCS medium. The combination of heat treatment at 56 degrees C and the addition of FS at a low concentration (1.25%) showed an additive effect on cell growth and resulted in the same cell density as that in 10% FCS medium, whereas the hGM-CSF concentration in the culture using FS-containing medium (FS medium) was approximately 50% that in 10% FCS medium. The total lipid concentration in FS was more than three fold that in FCS. The effect of decreasing FS concentration on cell growth may be due to the low lipid concentration in FS medium, because addition of the lipids extracted from FS to 10% FCS and 1.25% FS media markedly decreased cell density. Consequently, the addition of heat-treated FS at low concentrations to medium may be useful for the growth of CHO cells without FCS.

Optimization of PAM Scaffolds for Neural Tissue Engineering: Preliminary Study on an SH-SY5Y Cell Line

Engineering neural tissue is one of the most challenging goals of tissue engineering. Neural tissue is highly complex and possesses an organized three-dimensional (3D) distribution that is essential for tissue function. An optimal scaffold for tissue engineering has to provide this distribution until the cells are able to activate their normal functions and develop neural connections with the host tissue. Different strategies such as gene therapy and cell transplantation particularly in retinal tissue have been tested, but so far they have only induced retinal degeneration in animals. The objective of this work was to study neural cell assembly as a function of scaffold features and surface chemistry for application in retinal tissue engineering using microfabricated patterns with a well-defined geometry. Because retinal neurons are known to be arranged in hexagonal arrays, hexagonal scaffolds of poly(DL-lactide-co-glycolide) acid were fabricated using a pressure-assisted microsyringe (PAM) system. The behavior of a model cell, neuroblastoma originating from human retina (SH-SY5Y), was analyzed after seeding on the scaffolds, measuring cell density as a function of line width and length of the scaffold to identify the optimal hexagonal geometry. We also evaluated the influence of scaffold on cell metabolism using the methyl thiazolyl tetrazolium assay and on neurite extension. As far as two-dimensional scaffolds are concerned, the results show that although metabolic activity per cell remains constant, hexagons with sides of 500 microm and line widths of 20 +/- 5 microm are optimum for neural cell adhesion in terms of cell density. On 3D scaffolds, cell metabolism is about three times higher than controls, and the optimum number of layers in the scaffold is three or four.

Jeans type analysis of chemotactic collapse

We perform a linear dynamical stability analysis of a general hydrodynamic model of chemotactic aggregation [P.H. Chavanis, C. Sire, Physica A 384 (2007) 199]. Specifically, we study the stability of an infinite and homogeneous distribution of cells against “chemotactic collapse”. We discuss the analogy between the chemotactic collapse of biological populations and the gravitational collapse (Jeans instability) of self-gravitating systems. Our hydrodynamic model involves a pressure force which can take into account several effects like anomalous diffusion or the fact that the organisms cannot interpenetrate. We also take into account the degradation of the chemical which leads to a shielding of the interaction like for a Yukawa potential. Finally, our hydrodynamic model involves a friction force which quantifies the importance of inertial effects. In the strong friction limit, we obtain a generalized Keller–Segel model similar to the generalized Smoluchowski–Poisson system describing self-gravitating Langevin particles. For small frictions, we obtain a hydrodynamic model of chemotaxis similar to the Euler–Poisson system describing a self-gravitating barotropic gas. We show that an infinite and homogeneous distribution of cells is unstable against chemotactic collapse when the “velocity of sound” in the medium is smaller than a critical value. We study in detail the linear development of the instability and determine the range of unstable wavelengths, the growth rate of unstable modes and the damping rate, or the pulsation frequency, of the stable modes as a function of the friction parameter and shielding length. For specific equations of state, we express the stability criterion in terms of cell density.

Development of a Three‐Stage System for Wastewater Toxicity Monitoring: A Design and Feasibility Study

A three-stage system was developed to automate a batchwise toxicity testing protocol designed for assessing wastewater toxicity to activated sludge. The three-stage system used the luminescent bacterium Shkl. The three stages were cell storage, cell activation, and continuous toxicity testing. Shkl cells were stored in a bioreactor at 4 degrees C when the system was not in use and activated in another bioreactor for use in toxicity tests conducted in a continuous manner. The system could quickly be switched between the "off" and "on" modes, and operation of the system was easy. The stability of the system, in terms of cell density and bioluminescence in the storage and activation bioreactors, and the response of the activated cells to a metal and an organic toxicant were studied. The feasibility of the system design was demonstrated by simulating zinc toxicity episodes in synthetic wastewater. The needs for further modifications and improvements of the system were discussed.

The multiscale nature of diesel particulate filter simulation

Widespread market application of diesel particulate filters (DPFs) has been accompanied by the introduction of new filter materials and configurations in terms of cell density, wall thickness, pore size, porosity, catalyst coatings etc. Given this state-of-affairs, materials development, DPF design, system integration, regeneration control strategy optimisation and ash ageing assessment, based on a traditional design of experiments approach, become very time consuming and costly, due to the high number of tests required. This provides a privileged window of opportunity for the application of simulation tools. DPF behaviour depends strongly on the coupling of phenomena occurring over widely disparate spatial and temporal scales and the simulation approach must recognise and exploit these facts.

Topography of pig retinal ganglion cells

In the present work we analyzed the distribution of retinal ganglion cells (RGCs) in the pig retina. RGCs were retrogradely labeled in vivo by injecting Fluoro-Gold into the optic nerve. RGC density and the distribution of RGCs in terms of soma size were analyzed. Different regions of the porcine retina were identified following analysis of the distribution of RGCs in terms of cell density and soma size: in the central retina, we found a high-density horizontal RGC band lying dorsal to the optic disc. Moreover, in this region, a high proportion of RCGs with small soma size was observed. From the central to the more peripheral retina, we observed a decrease in RGC density, together with a greater presence of RGCs with larger somas. The results of this study should prove to be useful as a foundation for future studies with the porcine retina as a model in ophthalmic research. The study also highlights the necessity to label the RGC population specifically with retrograde tracers in order to quantify precisely alterations in the cell population associated with experimental treatments.

Programmed population control by cell-cell communication and regulated killing.

De novo engineering of gene circuits inside cells is extremely difficult, and efforts to realize predictable and robust performance must deal with noise in gene expression and variation in phenotypes between cells. Here we demonstrate that by coupling gene expression to cell survival and death using cell-cell communication, we can programme the dynamics of a population despite variability in the behaviour of individual cells. Specifically, we have built and characterized a 'population control' circuit that autonomously regulates the density of an Escherichia coli population. The cell density is broadcasted and detected by elements from a bacterial quorum-sensing system, which in turn regulate the death rate. As predicted by a simple mathematical model, the circuit can set a stable steady state in terms of cell density and gene expression that is easily tunable by varying the stability of the cell-cell communication signal. This circuit incorporates a mechanism for programmed death in response to changes in the environment, and allows us to probe the design principles of its more complex natural counterparts.