Bj. Cha et Dl. Gard, XMAP230 is required for the organization of cortical microtubules and patterning of the dorsoventral axis in fertilized Xenopus eggs, DEVELOP BIO, 205(2), 1999, pp. 275-286
The dorsoventral axis of Xenopus embryos is specified by a rotation of the
egg cortex relative to the underlying yolky cytoplasm. This cortical rotati
on, which occurs during the first cell cycle after fertilization, is depend
ent upon an array of parallel microtubules in the subcortical cytoplasm. We
have used confocal immunofluorescent microscopy and microinjection of affi
nity-purified anti-XMAP230 antibody to address the role of XMAP230, one of
three high-molecular-weight microtubule-associated proteins (MAPs) in Xenop
us eggs, in the assembly and organization of the cortical microtubule array
and specification of the dorsoventral axis. Confocal immunofluorescence mi
croscopy revealed that XMAP230 was associated with cortical microtubules sh
ortly after their appearance in the subcortical cytoplasm. XMAP230 staining
became more prominent as microtubules were aligned and bundled during the
cortical rotation. Loss of XMAP230 appeared to precede disassembly of corti
cal microtubules at the end of the first cell cycle. Deeper within the cyto
plasm, XMAP230 was associated with microtubules early in the assembly of th
e sperm aster. However, later in the first cell cycle, XMAP230 was associat
ed with microtubules (MTs) of the first mitotic spindle, spindle asters, an
d the cortical MTs, but not with microtubule remnants of the sperm aster. M
icroinjection of anti-XMAP230 antibody locally disrupted the assembly and o
rganization of microtubules in the cortex of activated or fertilized eggs a
nd resulted in defects in the dorsoventral patterning of embryos. These res
ults indicate that the assembly and/or organization of cortical microtubule
s in fertilized Xenopus eggs and subsequent specification of the dorsoventr
al axis are dependent upon XMAP230. (C) 1999 Academic Press.