Centrosomes act as microtubule organizing centers, and are critical for cell division and cell polarity. Identifying the regulators and components of centrosomes is an important step in understanding cell division. To this end, our lab has completed genome-wide modifier screens to identify genes that, when reduced in function using feeding RNAi, can suppress lethality in three conditional centrosome-defective mutants:
spd-2(
or183ts),
spd-5(
or213ts) and
zyg-1(
or278ts). The
spd-2 gene encodes a coiled-coil protein essential for centrosome duplicaion and maturation;
zyg-1 encodes a kinase required for daughter centriole formation; and
spd-5 encodes a coiled-coil protein required for centrosome maturation. We have isolated 9 non-essential genes and one essential gene that specifically suppress the embryonic-lethality associated with one or more of the three mutants. We are currently investigating these 10 genes for their roles in regulating microtubule dynamics and mitotic spindle assembly and positioning. One gene, H37N21.1/hpo-11, strongly and specifically suppresses the lethality of
spd-5 after RNAi knockdown. When we use RNAi to knock down H37N21.1/hpo-11 in wild-type embryos, we observe a substantial delay in rotation of the first mitotic spindle and a highly penetrant loss of spindle rocking during anaphase at the one-cell stage. These results suggest there may be abnormalities in microtubule dynamics in embryos lacking H37N21.1. Interestingly, H37N21.1 is conserved, with a mammalian ortholog called MADM (Mlf-1 adaptor molecule). MADM encodes a kinase-like protein localizes to centrosomes, and physically associates with the Mlf1 oncoprotein, which is involved in acute myeloid leukemia. However, the role of MADM at centrosome and in leukemia is little understood. We are investigating the cellular localization and function of H37N21.1, and of the other suppressors, to understand how they influence centrosome fuction and suppress lethality.