( ( The ( centriole pairs ) ) ( ( serve ( as ( ( ( microtubule-organizing centers ) ( -LRB- ( centrosomes -RRB- ) ) ) ( ( around which ) ( ( the ( mitotic spindle ) ) forms ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (JJ centriole) (NNS pairs)) (VP (VBP serve) (PP (IN as) (NP (NP (JJ microtubule-organizing) (NNS centers)) (PRN (-LRB- -LRB-) (NP (NNS centrosomes)) (-RRB- -RRB-)) (SBAR (WHPP (IN around) (WHNP (WDT which))) (S (NP (DT the) (JJ mitotic) (NN spindle)) (VP (VBZ forms))))))) (. .)))
The centriole pairs serve as microtubule-organizing centers (centrosomes) around which the mitotic spindle forms.
(ROOT (S (NP (DT A) (JJ mitotic) (NN spindle)) (VP (VBZ forms) (PP (IN from) (NP (DT the) (NNS centrosomes)))) (. .)))
A mitotic spindle forms from the centrosomes.