Function of tyrosine phosphorylation of BIT in photic entrainment of the circadian clock in rats

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Circadian rhythms of mammals are generated by a circadian oscillation of master pacemaker genes in the suprachiasmatic nucleus of the hypothalamus (SCN), and entrained by environmental factors such as 24-h light-dark cycles. We have previously shown that light exposure during the dark period enhanced tyrosine phosphorylation of brain immunoglobulin-like molecule with tyrosine-based activation motifs (BIT) in the rat SCN. Our major findings from last year were as follows, (1) BIT was tyrosine phosphorylated in response to light in the retina, (2) BIT was tyrosine phosphorylated on cold exposure in various nuclei of the hypothalamus, (3) BIT was associated with pl37GPI-anchored protein and clathrin heavy chain, (4) BIT was internalized by endocytosis and this process might be regulated by its tyrosine phosphorylation.