miR-124-regulated RhoG reduces neuronal process complexity via ELMO/Dock180/Rac1 and Cdc42 signalling

Abstract

Little is known about the cellular physiology of Escherichia coli at high cell densities (e.g., greater than 50 g [dry cell weight] per liter), particularly in relation to the cellular response to different growth conditions. E. coli W3100 cultures were grown under identical physical and nutritional conditions, by using a computercontrolled fermentation system which maintains the glucose concentration at 0.5 g/liter, to high cell densities at pH values of 6.0, 6.5, 7.0, and 7.5. The data suggest a relationship between the pH of the environment and the amount of acetate excreted by the organism during growth. At pH values of 6.0 and 6.5, the acetate reached a concentration of 6 g/liter, whereas at pH 7.5, the acetate reached a concentration of 12 g/liter. Furthermore, at pH values of 6.0 to 7.0, the E. coli culture undergoes a dramatic metabolic switch in which oxygen and glucose consumption and CO2 evolution all temporarily decrease by 50 to 80%, with a concomitant initiation of acetate utilization. After a 30-min pause in which approximately 50% of the available acetate is consumed, the culture recovers and resumes consuming glucose and oxygen and producing acetate and CO2 at preswitch levels. During the switch period, the specific activity of isocitrate lyase typically increases approximately fourfold.It is well known that during rapid aerobic growth, strains of Escherichia coli produce acetic acid as a by-product (7, 9-14, 17, 19), although the amount of acetate produced is strain dependent (17). Luli and Strohl (17) found that more than a threefold difference in acetate concentrations may occur between different strains grown in batch fermentations under identical conditions. The growth rate of the culture and the composition of the medium also influence the amount of acetate produced during growth. In chemostat experiments, acetate is not produced until the growth rate reaches a threshold value that is dependent upon the type of growth medium (21). E. coli cultures will produce acetate at a lower growth rate when grown in a nutrient-rich medium than in a defined medium (9, 21), and the specific acetate production rate also changes with the growth rate (9).Acetate is produced when the uptake of the primary carbon source is greater than its conversion to biomass and CO2 (10). The rate-limiting aspect of metabolism contributing to acetic acid formation by E. coli has been attributed to the electron transport system (7), the tricarboxylic acid cycle (10), or a combination of both (19). In a batch culture growing on glucose, approximately 15% of the carbon input is typically excreted as acetate (10).The presence of acetate in the growth medium can influence the physiology of the cell in many ways. Elevated acetate concentrations inhibit the growth rate of the culture, the effect of which may be more pronounced in complex medium than in defined medium (23). It has been postulated that the protonated form of acetate can cross the cytoplasmic membrane and reduce the proton motive force by decreasing ApH (7, 17), a...

MicroRNAs in neural development: from master regulators to fine-tuners

“…In support of this, it has been reported that brain-derived neurotrophic factor (BDNF)-induced axonal branching in the developing mouse retina depends on increased levels of miR-132, which promotes axonal branching by inhibiting the translation of its known target Rho family GTPaseactivating protein, p250GAP (Arhgap32) (Marler et al, 2014). Increased levels of other miRNAs, such as miR-124 in hippocampal neurons (Franke et al, 2012) and miR-29a in cortical neurons (Li et al, 2014), can also induce axonal branching. miRNAs are also involved in the directional growth of axons, a process known as axon guidance.…”

BDNF Promotes Axon Branching of Retinal Ganglion Cells via miRNA-132 and p250GAP

“…Protein levels were investigated using Western blot analysis after 2 or 3 d, as described by Carvalho et al (2006). Figure 3 shows the results from a set of experiments using 10 g of DNA after 3 d in culture.…”

“…Chick and mouse primary retinal cultures were generated as described previously (Marler et al, 2008). In brief, for mouse cultures, embryonic day 15.5 (E15.5) to E16.5 mouse embryos from timed-mated CD-1 mice were used, with the day of the plug counted as E0.5.…”

“…In brief, for miRNA overexpression, a mature mouse miRNA-132 sequence was inserted downstream of the U6 RNA polymerase promoter into a vector coexpressing RFP downstream of a CAG promoter based on Liu et al (2010). A scrambled sequence was used to generate the control noncoding vector (Barkho et al, 2008).…”

Emerging roles for miRNA-based post-transcriptional regulation in neuronal morphogenesis and neurodevelopmental disorders

“…An elegant study by Sanuki et al showed that miR-124 regulates axon development by inhibiting LIM/homeobox protein 2 (Lhx2) expression in vivo [13] . Another report demonstrated that miR-124 controls axon growth by targeting mRNA of small GTPase RhoG [14] .…”