Tankyrase-1 polymerization of poly(ADP-ribose) is required for spindle structure and function

Poly(ADP-ribose) (PAR) is a large, negatively charged posttranslational modification that is produced by polymerization of NAD+ by PAR polymerases (PARPs)(1). There are at least 18 PARPs in the human genome, several of which have functions that are unknown(1). PAR modifications are dynamic; PAR structure depends on the balance between synthesis and hydrolysis by PAR glycohydrolase(2). We previously found that PAR is enriched in vertebrate somatic-cell mitotic spindles and demonstrated a requirement for PAR in the assembly of Xenopus egg extract spindles(3). Here, we knockdown all characterized PARPs using RNA interference (RNAi), and identify tankyrase-1 as the PARP that is required for mitosis. Tankyrase-1 localizes to mitotic spindle poles, to telomeres(4) and to the Golgi apparatus(5). Tankyrase-1 RNAi was recently shown to result in mitotic arrest, with abnormal chromosome distributions and spindle morphology observed - data that is interpreted as evidence of post-anaphase arrest induced by failure of telomere separation(6). We show that tankyrase-1 RNAi results in pre-anaphase arrest, with intact sister-chromatid cohesion. We also demonstrate a requirement for tankyrase-1 in the assembly of bipolar spindles, and identify the spindle-pole protein NuMA(7) as a substrate for covalent modification by tankyrase-1.