Effect of hexylene glycol‐altered microtubule distributions on cytokinesis and polar lobe formation in fertilized eggs of Ilyanassa obsoleta

Abstract

Some effects of gravity on early morphogenesis are correlated with microtubule locations within cells. During first cleavage in Ilyanassa obsoleta embryos, a transitory polar lobe constriction forms and then relaxes, allowing the polar lobe to merge with one daughter cell. If the polar lobe is equally divided or removed, morphogenesis is severely disrupted. To examine microtuble locations during early Ilyanassa development, eggs were fixed and stained for polymerized alpha-tubulin during first cleavage. The mitotic apparatus assembles at the animal pole. The cleavage furrow forms between the asters, constricting to a stabilized intercellular bridge encircling midbody-bound microtubules, whereas the polar lobe constriction forms below and parallel to the spindle, constricting to a transitory intercellular bridge encircling no detectable microtubules. At metaphase an alpha-tubulin epitope is distributed throughout the spindle, whereas a beta-tubulin epitope is present predominantly in the asters. Incubation in hexylene glycol, a drug that increases microtubule polymerization, during mitosis causes the polar lobe constriction to tighten around polymerized alpha-tubulin and remain stably constricted. If hexylene glycol is removed, alpha-tubulin staining disappears from the polar lobe constriction, which relaxes, whereas microtubules remain in the cleavage furrow, which remains constricted. These observations suggest that asymmetric distribution of microtubules affects early Ilyanassa cleavage patterns, and that continued presence of microtubules extending through an intercellular bridge is important for stabilization of the bridge constriction prior to completion of cytokinesis. These data provide the basis for further analysis of the role of microtubules in possible microgravity disruptions of Ilyanassa development.

Differential localization of cytoplasmic myosin ii isoforms a and b in avian interphase and dividing embryonic and immortalized cardiomyocytes and other cell types in vitro

“…With respect to distribution, in our study, interphase chick embryonic cardiac fibroblasts, in primary cell culture, that express both CMIIA and CMIIB localize these two isoforms together and in the same relative distributions in both of the cytoskeletal configurations typical of CMII, SFs, and networks. This may be contrasted with the cytoskeletal protein, filamin, whose isoforms are distributed differentially along SFs in embryonic chick cells [Pavalko et al, 19891, with some tropomyosin isoform distributions in chick embryonic fibroblasts and human bladder carcinoma cells [Lin et al, 19881, and with the cytoskeletal protein, tubulin, whose a, p, and y-isoforms are localized differentially within the mitotic apparatus of dividing cells [Conrad et al, 1994;Oka et al, 1990;Julian et al, 19931. Moreover, in transformed human cancer cell lines in long-term culture CMIIA and B are distributed together in centrally positioned SFs, but differentially in peripheral SFs, and in the interphase cell cortex [Maupin et al, 19941.…”

Single Cell in a Gravity Field

“…In the early embryogenesis of a shellfish under microgravity conditions, asymmetric distribution of microtubules is observed, which affects the patterns of cleavage during morphogenesis [ 29 ], which can lead to morphological developmental anomalies, but possibly not of all organs. Thus, in the larvae of the newt, after 15 days of exposure to space flight conditions (IML-2 mission), the dimensions of the labyrinth were comparable to those in the control [ 30 ].…”

Induction of Cytokinesis Is Independent of Precisely Regulated Microtubule Dynamics

“…Hexylene glycol (HG) has been reported to increases MT stability (Oka et al, 1991;Conrad et al, 1994;Tirnauer et al, 2004). We treated metaphase eggs with HG and then added a dose of nocodazole (NZ) sufficient to depolymerize the asters in control cells ( Figure 4A).…”