Moreover alteration of the human serotoninergic system seem to correlate to neuropsichiatric disorders, as alimentary disorders, aggressiveness and depression.

ABSTRACT

In vertebrate hindbrain the serotoninergic neurons are organized in nuclei (Raphe Nuclei) located in the reticular system. The Raphe Nuclei innervate a great number of regions of the brain and the spinal cord.

Moreover alteration of the human serotoninergic system seem to correlate to neuropsichiatric disorders, as alimentary disorders, aggressiveness and depression.

At the present day, the genetic mechanisms that control the specification and differentiation of serotoninergic neurons during embryonic development are not well clarified.

During the central nervous system development, neurons that produce serotonin (5-HT) originate from the ventral portion of the hindbrain. It has been shown that diffusible molecules such as Shh, FGF8, FGF4 activate some transcriptional factors as Mash1, Nkx2.2, Nkx6.1, GATA2, GATA3 important for serotoninergic precursor specification.

Recently the gene Pet-1 has been identified in mouse: it is a transcription factor that contains an ETS domain and that is expressed in serotoninergic precursors one day after the initial synthesis of serotonin. Knockout experiments in mouse have demonstrated the Pet-1 is needed for terminal differentiation and, presumably, phenotipic determination of serotoninergic neurons and serotonin synthesis in the CNS.

To give a contribution in understanding the molecular mechanism involved in the development of serotoninergic neurons, my thesis work focused on the study of the functional role of Pet-1 gene in an experimental animal model as Xenopus laevis . First, I screened a cDNA library to isolate the mouse Pet-1 homolog in Xenopus laevis.

Then, I have studied the XPet-1 expression pattern during embryonic development and adult stage by in situ hybridation. The results indicate that, in Xenopus, XPet-1 is expressed only in serotoninergic ________________________________________________________________________

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neurons that originate in the hindbrain Raphe Nuclei. To identify the precise spatio-temporal window in which XPet-1 expression occurs, I have performed double in situ hybridation experiments with XPet-1 and with XEn which is expressed in mid-hindbrain boundary and with XKrox20 which is specifically expressed in rombomers ( r ) 3 and 5.

The expression of XPet-1 is detected after stage 24 (tailbud) in the ventral region of the neural tube near the mid-hindbrain boundary. In subsequent stages the XPet-1 expression extended also in a region posterior to the hindbrain.

Thank to the possibility to perform microinjection experiments in embryos, Xenopus laevis is particulary indicated for studying specific gene functional roles. To study XPet-1 function during Xenopus embryonic development, I have performed overexpression experiments by XPet-1 mRNA microinjection. The analisis of the injected embryos demonstrated that XPet-1 is not able to produce ectopical serotoninergic neurons.

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