PhD Discussions: Ágata Mata and Lucas Pedraz

Role of secreted Sema3E in embryonic and adult hippocampal formation

Due to its implication in many cognitive processes like learning and memory, the hippocampal formation is a brain structure which has been widely studied over the years. Its simplified architecture, where principal cells are in a single cell layer and synaptic inputs are in well defined dendritic lamina, has enabled the study and establishment of the general principles of modern neuroscience. Behind this simplicity resides the action of numerous factors that regulate the correct development of the structure.

The principle entrance of information to the hippocampus is the entorhino-hippocampal (EH) pathway or perforant pathway, where axons arising from the entorhinal cortex enter the hippocampus proper and arrive to the outer molecular layer of the dentate gyrus. The development of this pathway is highly regulated and some of the molecules that intervene in this process are the class III Semaphorins.

Class III Semaphorins are soluble molecules initially known by its function in axonal guidance. It is known that some of these molecules and their receptors are involved in the development and maturation of the hippocampal connections, nevertheless, the participation of Sema3E and its receptor, PlexinD1, in the development of the entorhino-hippocampal connection has not been studied in detail. With this in mind, in the present study we focused on determining their role during development and adulthood.

Our results show that in absence of Sema3E/PlexinD1 signalling (i) there is an aberrant layering of the entorhinal axons in the hippocampus during development, and (ii) there are some alterations in the adult hippocampal formation such as misrouted ectopic mossy fibres and ectopic granule cells in the dentate gyrus due to a dysregulation in the proliferation of dentate gyrus progenitors.

Regulation of DNA synthesis in bacterial biofilms: An in vitro system for modelization of the oxygen gradients present in the chronic infections biofilms

Chronic infections represent one of the main threats to human health nowadays, being one of the main causes of death even in the developed countries. These infections are always associated with the developing of a biofilm, complex 3D structures where cells are encapsulated in an extracellular polymeric matrix, seeing increased their resistance to antibiotic therapies and physical stress. In biofilms, oxygen cannot diffuse freely throughout the structure, generating an oxygen concentration gradient and leading to the presence of microaerophilic and anaerobic environments.

Given the urgent need to develop new antimicrobial therapies, many aspects of bacterial physiology are being studied trying to understand better the underlying molecular mechanisms of their growing and virulence. However, one of the major factors affecting the differential behavior in the biofilm is the oxygen concentration, and, in most cases, studies have only been conducted using biofilms as a whole, or using fully aerobic or fully anaerobic liquid cultures; in real world conditions, transition from aerobiosis to anaerobiosis is never done in a single step, having always a spatial and/or temporal gradient of oxygen concentrations, and gene regulation during intermediate stages of this gradient, in microaerophilic environments or during dynamical oxygen concentration changes, has not been studied properly.

In our lab we have developed a method to monitor bacterial gene expression as determined by oxygen concentration, during a progressive change in oxygenation conditions, that can be implemented in any microbiology lab and that only relies on common laboratory equipment. The method is based on a chemostat-like bioreactor coupled to an oxygen tension continuous detection system that also allows for discontinuous sampling. Initially, this system is now being applied to the determination of the changes in ribonucleotide reductase gene expression profile determined by oxygen concentration in a Pseudomonas aeruginosa liquid culture.

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