A primary microcephaly-associatedsas-6mutation perturbs centrosome duplication, dendrite morphogenesis, and ciliogenesis inCaenorhabditis elegans

Abstract

The human SASS6(I62T) missense mutation has been linked with the incidence of primary microcephaly in a Pakistani family, although the mechanisms by which this mutation causes disease remain unclear. The SASS6(I62T) mutation corresponds to SAS-6(L69T) inC. elegans. Given that SAS-6 is highly conserved, we modeled this mutation inC. elegansand examinedsas-6(L69T)effect on centrosome duplication, ciliogenesis and dendrite morphogenesis. Our studies revealed that all the above processes are perturbed by thesas-6(L69T)mutation. Specifically,C. eleganscarrying thesas-6(L69T)mutation exhibit an increased failure of centrosome duplication in a sensitized genetic background. Further, worms carrying this mutation also display shortened phasmid cilia, an abnormal phasmid cilia morphology, shorter phasmid dendrites and chemotaxis defects. Our data show that the centrosome duplication defects caused by this mutation are only uncovered in a sensitized genetic background, indicating that these defects are mild. However, the ciliogenesis and dendritic defects caused by this mutation are evident in an otherwise wild-type background, indicating that they are stronger defects. Thus, our studies shed light on the novel mechanisms by which thesas-6(L69T)mutation could contribute to the incidence of primary microcephaly in humans.