EVIDENCE OF DIFFERENTIAL EXPRESSION RELATED TO THYROSINE HYDROXILASE GENES IN CHICK (GALLUS GALLUS) BRAIN STEM DURING EMBRYO DEVELOPMENT

By affecting efficiency of DOPA synthesis, tyrosine hydroxylase (TH) is the effective modulator of the limiting step of the biosynthetic pathways of catecholamines (dopamine, noradrenaline and adrenaline), highly conserved in vertebrate species. Catecholamines are involved in many physiological functions in the central and peripheral nervous systems as well as in the endocrine system, thus regulation of TH expression and activity are crucial for neuronal and hormonal functions that involve the entire dopaminergic, noradrenergic and adrenergic systems. THrelated expression is due to two non-allelic genes, called TH1 and TH2, reported in almost all vertebrates except placental mammalian, which have lost TH2 gene during evolution. THrelated genes have crucial ontogenetic roles, being linked to pathological onsets during embryo development. Here, we show the expression analysis of TH-related transcripts in brain stem of gallus gallus, as a key model of vertebrate central nervous system development. By real time RT-PCR assays, we assessed that TH1 and TH2 mRNAs show progressive increase during embryo development (from 8 to 21 days post fertilization) with differential trend. Moreover, a substantially different regulatory switch of expression was shown for the two genes when passing to the adult developmental phase. According to what stated in teleost fish, different expression patterns suggest different mechanism of transcriptional regulation related to potentially differing roles during development for TH1 and TH2 genes: based on our comparative results, TH1 mRNA expression in gallus gallus brain increases gradually during development reaching significantly high post-embryonic levels, whereas the TH2 mRNA seems to be more specifically linked to embryogenesis of vertebrate brain stem.