Zinc homeostasis during brain cortico-genesis – ImaZinc

Zinc (Zn) is a vital element controlling a wide diversity of biological processes. It is, after iron, the most abundant trace metal of the human body. For instance, the brain is a zinc-rich organ. This metal is mainly bound to proteins where it plays structural and catalytic roles. However, some zinc ions can be displaced from their binding sites, like metallothioneins or mitochondria, and released intracellularly. Several pathophysiological conditions such as heavy metals, anoxic conditions, or oxidative insults can mobilize zinc from these pools which gives rise to fluctuations of the cytosolic concentration of free Zn. These events represent biological signals able to influence the activity of signaling molecules like enzymes (e.g. phosphatases) and transcription factors (e.g. MT-F1). Therefore, Zn is now regarded as second messenger controlling intracellular signaling pathways. Another important aspect of the biology of Zn is its storage into the synaptic vesicles of some neuronal cells of the central nervous system. These neurons accumulating Zn are mainly found in the cortex and hippocampus. This is an important feature because, in these brain areas, the release of the neurotransmitter is associated with a release of Zn into the synaptic cleft. Furthermore, the activity of many neurotransmitter receptors and ion channels is regulated by extracellular Zn ions. This alters synaptic transmission and its plasticity, making zinc an endogenous and physiological regulator of neuronal activity. But in addition to this, this metal is a key player in the formation, growth and survival of neural cells. However, the molecular actors controlling the homeostasis of Zn in the brain are poorly characterized as well as the roles played in its influx/efflux and intracellular storage. In addition, its quantitative spatial distribution is poorly documented. This is a key information in order to identify anterior-posterior and dorso-ventral gradients within brain structures. Besides these quantitative and spatial issues, even less is known about its temporal regulation.
Our proposal is based on a multidisciplinary approach gathering neurobiologists, chemists and physicists around highly complementary techniques with the aim to carry out a multi-scale analysis (from the sub-cellular to the organ level) of the distribution of Zn in the murine cortex. We will use common biochemical methods like extraction of mRNAs, proteins (for PCR and Western blotting) as well as state of the art high-resolution microscopic techniques: synchrotron-based chemical nanoimaging and laser-induced breakdown spectroscopy (LIBS). By defining the molecular actors participating in the transport of Zn as well as its 2D- and 3D-imaging, this project will provide an in depth understanding of the homeostasis of Zn during the formation of the cortex. In mice, the formation of the brain structure takes place between embryonic days E12/13 and E17/18. We will perform our experiments on cells and whole tissues collected at this 2 time points. Overall, this project will provide a detailed molecular, quantitative, spatial and temporal description of the homeostasis of Zn during the formation of the brain cortex. The highly innovative imaging techniques that will be used throughout this project will be of great help to study other brain regions or organs, in health and diseases states. It is now well recognized that technological advances, notably from the photonics filed, offer unprecedented opportunities for the understanding biological processes.