Neurogenesis in the brain of the Marbled crayfish

Abstract

The main aim of the project was to study the formation of the main brain scaffold and the mechanisms underlying this process. The brain forms during embryogenesis from an initial thin layer of cells (neuroectoderm) that unfolds into a three dimensional complex structure. This process involves both an intense mitotic activity of progenitor cells (neuroblasts) and a series of morphogenetic movements that lead to a mature and functioning structure of the brain. Analyses were based on immunohistochemical techniques, use of proliferation markers (e.g. 5-bromo-2-deoxyuridine and 5-ethynyl-2’-deoxyuridine) and confocal laser-scan microscopy. Moreover, the use of a specific monoclonal antibody against the protein expressed by engrailed (a segment polarity gene) identified single neuronal cells that were compared with data available for Insecta. In this way, both information on the neurobiology of the Marbled crayfish and on its phylogeny were acquired. One important feature of the crayfish brain is the high plasticity that it shows not only during embryogenesis but throughout its life span. The brain in fact does not stop to develop and after embryogenesis the central olfactory pathway receives newly born olfactory local interneurons and projection neurons that replace old neurons or simply are added to the previous neuronal population. These neurons are provided by a specific post-embryonic structure, the neurogenic niche. By monitoring the activity of NBs, it was possible to discover when and how the niche starts forming and functioning. The topic of adult neurogenesis is a fascinating field of research which involves stem cells biology and regulatory mechanisms that are just now started to be explored. This challenging field of research holds many future perspectives, because some of the main characteristics of the adult neurogenesis in crustaceans are shared with vertebrates, in particular with mammals.