While
cdk5 was originally identified in vertebrates based on its homology to the cell cycle regulated
cdc2, further study has demonstrated a function not in the cell cycle but instead in post-mitotic neurons. Mouse knockouts of
cdk5 and its activator,
p35, result in defects in the pattern of neuronal migration in the cortex (1,2). Studies in cultured rat neurons demonstrated that the
cdk5/p35 kinase activity can promote neurite outgrowth (3). At this point, however, little is known about the upstream activators and downstream targets of the
cdk5/p35 kinase. The Caenorhabditis elegans homolog of
cdk5 is 74% identical to mouse, and the
p35 homolog contains a 159 aa region that is 54% identical. Translational GFP reporter constructs for
cdk5 and
p35 are expressed in the cytoplasm of most neurons beginning around the two-fold stage of embryogenesis and continuing into adulthood. To produce a loss of function phenotype, we injected dsRNA for either
cdk5,
p35, or both into N2 worms. In each case, most of the progeny had no gross visible phenotype, although a few Dpy Unc worms were produced. To identify loss of function mutations in
cdk5 and
p35, we will also screen a deletion library by PCR. To generate an overexpression phenotype, DNA containing the
cdk5 or
p35 genomic region was injected into N2 worms to produce extrachromosomal arrays. Worms carrying a
cdk5 array (40 microg/ml) have no visible phenotype, and worms carrying a
p35 array (40 microg/ml) are occasionally slightly uncoordinated (Unc). Worms carrying an array with both
cdk5 and
p35, however, are strongly Unc. These worms have defects in fasciculation and axon pathfinding. Along with the expression pattern, this strongly suggests a role for
cdk5 and
p35 in neuronal development. We will screen for suppressors of this Unc phenotype to identify other genes that are acting in the
cdk5/p35 pathway. (1) Gilmore EC, Ohshima T, Goffinet AM, Kulkarni AB, Herrup K, J Neurosci, 18:6370-7 (1998) (2) Chae T, Kwon YT, Bronson R, Dikkes P, Li E, Tsai LH, Neuron, 18:29-42 (1997) (3) Nikolic M, Dudek H, Kwon YT, Ramos YF, Tsai LH, Genes Dev, 10:816-25 (1996)