Jackson Lab Research Interests / RNA-binding Proteins and Clock Output

We have been interested for many years in the molecular genetic dissection of clock output (signaling) pathways that mediate the circadian regulation of defined behaviors: adult eclosion (the emergence of adult insects from the pupal case) and locomotor activity.  We have shown, for example, that the abundance of a Drosophila neuronal RNA-binding protein called LARK is regulated by the circadian clock and that this protein is required for normal behavioral rhythmicity (Newby and Jackson, 1993; Newby and Jackson, 1996; McNeil et al., 1998; Zhang et al., 2000; Schroeder et al., 2003). Flies that express abnormally high or low levels of LARK in known circadian clock neurons, generated by over expression or RNA interference-mediated knockdown of the protein, are weakly rhythmic or arrhythmic. Given that the molecular oscillator is apparently intact in LARK over expressing flies (Schroeder et al., 2003), we postulate that LARK serves as a component of an intracellular signaling pathway that regulates synaptic output of clock neurons (Jackson et al., 2005). We are currently using genetic techniques to identify additional components of this pathway. We have recently identified target RNAs regulated by LARK, using a microarray-based molecular approach, and many of the targets encode functions relevant for synaptic transmission or signaling. In other studies, we are trying to define the mechanisms that regulate circadian changes in LARK abundance, in order to connect this output pathway to the clock mechanism. Interestingly, the lark gene has mouse and human orthologs (Jackson et al., 1997), with postulated roles in splicing, transcriptional regulation and translational control. Recent unpublished studies by another group, for example, indicate that mammalian LARK regulates the translation of the Per1 clock gene within the suprachiasmatic nuclei (the anatomical location of the mammalian circadian pacemaker).

In related work, we are continuing to study the Drosophila homolog of the human Fragile X Mental Retardation Protein (FMRP), a RNA-binding protein of the KH/RGG class. This work is being carried out in collaboration with Dr. Bassem Hassan (Flanders Interuniversity Institute of Biotechnology, Belgium) and it has shown that Drosophila Fragile X gene (dfmr1) mutants have altered circadian rhythmicity (Joannella et al., 2002). More recent work has identified RNA targets of the fly FMRP protein (Reeve et al., 2005). One of the targets is Profilin, an actin cytoskeletal regulatory protein, and genetic analyses have demonstrated that FMRP regulates axonal outgrowth and neurite extension via Profilin. We remain interested in defining the FMRP target RNAs that are relevant for behavioral rhythmicity. With David Nelson (Baylor), we are looking at functional interactions between FMRP and LARK as the two proteins interact in yeast two-hybrid assays and in in vivo (Sofola et al., 2007).