Studies on the PII-PipX-NtcA Regulatory Axis of Cyanobacteria Provide Novel Insights into the Advantages and Limitations of Two-Hybrid Systems for Protein Interactions.

Yeast two-hybrid approaches, which are based on fusion proteins that must co-localise to the nucleus to reconstitute the transcriptional activity of GAL4, have greatly contributed to our understanding of the nitrogen interaction network of cyanobacteria, the main hubs of which are the trimeric PII and the monomeric PipX regulators. The bacterial two-hybrid system, based on the reconstitution in the cytoplasm of the adenylate cyclase of , should provide a relatively faster and presumably more physiological assay for cyanobacterial proteins than the yeast system. Here, we used the bacterial two-hybrid system to gain additional insights into the cyanobacterial PipX interaction network while simultaneously assessing the advantages and limitations of the two most popular two-hybrid systems.

The Signal Transduction Protein PII Controls the Levels of the Cyanobacterial Protein PipX.

Cyanobacteria, microorganisms performing oxygenic photosynthesis, must adapt their metabolic processes to environmental challenges such as day and night changes. PipX, a unique regulatory protein from cyanobacteria, provides a mechanistic link between the signalling protein PII, a widely conserved (in bacteria and plants) transducer of carbon/nitrogen/energy richness, and the transcriptional regulator NtcA, which controls a large regulon involved in nitrogen assimilation. PipX is also involved in translational regulation through interaction with the ribosome-assembly GTPase EngA.

The ribosome assembly GTPase EngA is involved in redox signaling in cyanobacteria.

Photosynthetic organisms must cope with environmental challenges, like those imposed by the succession of days and nights or by sudden changes in light intensities, that trigger global changes in gene expression and metabolism. The photosynthesis machinery is particularly susceptible to environmental changes and adaptation to them often involves redox-sensing proteins that are the targets of reactive oxygen species generated by photosynthesis activity. Here we show that EngA, an essential GTPase and ribosome-assembly protein involved in ribosome biogenesis in bacteria and chloroplasts, also plays a role in acclimatization to environmentally relevant stress in PCC7942 and that PipX, a promiscuous regulatory protein that binds to EngA, appears to fine-tune EngA activity.

Regulatory Connections Between the Cyanobacterial Factor PipX and the Ribosome Assembly GTPase EngA.

Cyanobacteria, phototrophic organisms performing oxygenic photosynthesis, must adapt their metabolic processes to important environmental challenges, like those imposed by the succession of days and nights. Not surprisingly, certain regulatory proteins are found exclusively in this phylum. One of these unique proteins, PipX, provides a mechanistic link between signals of carbon/nitrogen and of energy, transduced by the signaling protein PII, and the control of gene expression by the global nitrogen regulator NtcA.

Distinctive Features of PipX, a Unique Signaling Protein of Cyanobacteria.

PipX is a unique cyanobacterial protein identified by its ability to bind to PII and NtcA, two key regulators involved in the integration of signals of the nitrogen/carbon and energy status, with a tremendous impact on nitrogen assimilation and gene expression in cyanobacteria. PipX provides a mechanistic link between PII, the most widely distributed signaling protein, and NtcA, a global transcriptional regulator of cyanobacteria. PII, required for cell survival unless PipX is inactivated or down-regulated, functions by protein-protein interactions with transcriptional regulators, transporters, and enzymes.

The nitrogen regulator PipX acts in cis to prevent operon polarity.

Cyanobacteria, phototrophic organisms performing oxygenic photosynthesis, must adapt their metabolic processes to important environmental challenges, like those imposed by the succession of days and nights. Not surprisingly, certain regulatory proteins are found exclusively in this phylum. One of these unique factors, PipX, provides a mechanistic link between signals of carbon/nitrogen and of energy, transduced by the signalling protein PII, and the control of gene expression by the global nitrogen regulator NtcA.

Energy drives the dynamic localization of cyanobacterial nitrogen regulators during diurnal cycles.

Cyanobacteria, phototrophic organisms performing oxygenic photosynthesis, must adapt their metabolic processes to the challenges imposed by the succession of days and nights. Two conserved cyanobacterial proteins, PII and PipX, function as hubs of the nitrogen interaction network, forming complexes with a variety of diverse targets. While PII proteins are found in all three domains of life as integrators of signals of the nitrogen and carbon balance, PipX proteins are unique to cyanobacteria, where they provide a mechanistic link between PII signalling and the control of gene expression by the global nitrogen regulator NtcA.

PipY, a Member of the Conserved COG0325 Family of PLP-Binding Proteins, Expands the Cyanobacterial Nitrogen Regulatory Network.

PCC 7942 is a paradigmatic model organism for nitrogen regulation in cyanobacteria. Expression of genes involved in nitrogen assimilation is positively regulated by the 2-oxoglutarate receptor and global transcriptional regulator NtcA. Maximal activation requires the subsequent binding of the co-activator PipX.

Cross-talk and regulatory interactions between the essential response regulator RpaB and cyanobacterial circadian clock output.

The response regulator RpaB (regulator of phycobilisome associated B), part of an essential two-component system conserved in cyanobacteria that responds to multiple environmental signals, has recently been implicated in the control of cell dimensions and of circadian rhythms of gene expression in the model cyanobacterium Synechococcus elongatus PCC 7942. However, little is known of the molecular mechanisms that underlie RpaB functions. In this study we show that the regulation of phenotypes by RpaB is intimately connected with the activity of RpaA (regulator of phycobilisome associated A), the master regulator of circadian transcription patterns.

Are migrants health policies aimed at improving access to quality healthcare? An analysis of Spanish policies.

Although until April 2012, all Spanish citizens regardless of their origin, residence status and work situation were entitled to health care, available evidence suggested inadequate access for immigrants. Following the Aday and Andersen model, we conducted an analysis of policy elements that affect immigrants' access to health care in Spain, based on documentary analysis of national policies and selected regional policies related to migrant health care. Selected documents were (a) laws and plans in force at the time containing migrant health policies and (b) evaluations.

Environmental control of phosphorylation pathways in a branched two-component system.

NblS, the most conserved histidine kinase in cyanobacteria, regulates photosynthesis and acclimatization to a variety of environmental conditions. We used in silico, in vivo and in vitro approaches to identify RpaB and SrrA as the cognate response regulators of NblS and to characterize relevant interactions between components of this signalling system. While genetic analysis showed the importance of the NblS to RpaB phosphorylation branch for culture viability in Synechococcus elongatus PCC 7942, in vitro assays indicated a strong preference for NblS to phosphorylate SrrA.

The regulatory factor SipA provides a link between NblS and NblR signal transduction pathways in the cyanobacterium Synechococcus sp. PCC 7942.

Cyanobacteria respond to environmental stress conditions by adjusting its photosynthesis machinery. When subjected to nutrient and high light stress, Synechococcus sp. PCC 7942 and other non-diazotrophic cyanobacteria degrade their phycobilisome, the light-harvesting complexes for photosynthesis.

Morphologic and neurochemical abnormalities in the auditory brainstem of the genetically epilepsy-prone hamster (GPG/Vall).

Purpose: This study was performed to evaluate whether audiogenic seizures, in a strain of genetically epilepsy-prone hamsters (GPG/Vall), might be associated with morphologic alterations in the cochlea and auditory brainstem. In addition, we used parvalbumin as a marker of neurons with high levels of activity to examine changes within neurons.

Methods: Cochlear histology as well as parvalbumin immunohistochemistry were performed to assess possible abnormalities in the GPG/Vall hamster.

Gbx2 is required for the morphogenesis of the mouse inner ear: a downstream candidate of hindbrain signaling.

Gbx2 is a homeobox-containing transcription factor that is related to unplugged in Drosophila. In mice, Gbx2 and Otx2 negatively regulate each other to establish the mid-hindbrain boundary in the neural tube. Here, we show that Gbx2 is required for the development of the mouse inner ear.

Distribution of glycoconjugates during cochlea development in mice: light microscopic lectin study.

During development, different epithelial cells in the mouse cochlea express different cell surface glycoconjugates, which may reflect membrane specialization. Some of the lectins tested in this study (SBA, succ-WGA, and PSA) labeled the sensory cells of the cochlea around birth. Other lectins (WGA, Con A, RCA-II, and PHA-E) labeled surfaces of the sensory cells, particularly the stereocilia, from early stages of development (gestation day (GD) 16) through 21 days after birth.

Olivocochlear efferent innervation of the organ of corti in hypothyroid rats.

Congenital hypothyroidism induces developmental abnormalities in the auditory receptor, causing deafness due to a poor development of the outer hair cells (OHCs) and a lack of synaptogenesis between these cells and the olivocochlear axons. This efferent innervation is formed by two separate systems: the lateral system, which originates in the lateral superior olive (LSO) and reaches the inner hair cells; and the medial system, which originates in the ventral nucleus of the trapezoid body (VNTB) and innervates the OHCs. A previous study carried out in our laboratory showed that in congenitally hypothyroid animals, the neurons which give rise to the efferent system are normal in number and distribution, although smaller in size.

Hypothyroidism prevents developmental neuronal loss during auditory organ development.

The deficit of thyroid hormone leads to several structural and physiological modifications in the auditory receptor: the outer hair cells present an immature morphology, abnormal persistence of the afferent dendrites and incomplete development of the efferent terminals. The aim of this work was to perform a quantitative and morphometric study of the spiral ganglion neurons in control and hypothyroid animals. The cochleae from both experimental groups were processed in order to obtain plastic sections.