Reversal of anchorage-independent multicellular spheroid into a monolayer mimics a metastatic model.

Lack of an in vitro model of metastasis has been a major impediment in understanding the molecular regulation of metastatic processes, and identification of specific therapeutic targets. We have established an in vitro model which displayed the signatures of metastatic phenotype such as migration, invasiveness, chemoresistance and expression of cancer stem-cell markers. This in vitro model was developed by the induction of reversal of multicellular spheroids that were generated by anchorage-independent growth.

Mitotic chromosome size scaling in Xenopus.

As rapid divisions without growth generate progressively smaller cells within an embryo, mitotic chromosomes must also decrease in size to permit their proper segregation, but this scaling phenomenon is poorly understood. We demonstrated previously that nuclear and spindle size scale between egg extracts of the related frog species Xenopus tropicalis and Xenopus laevis, but show here that dimensions of isolated mitotic sperm chromosomes do not differ. This is consistent with the hypothesis that chromosome scaling does not occur in early embryonic development when cell and spindles sizes are large and anaphase B segregates chromosomes long distances.

A role for central spindle proteins in cilia structure and function.

Cytokinesis and ciliogenesis are fundamental cellular processes that require strict coordination of microtubule organization and directed membrane trafficking. These processes have been intensely studied, but there has been little indication that regulatory machinery might be extensively shared between them. Here, we show that several central spindle/midbody proteins (PRC1, MKLP-1, INCENP, centriolin) also localize in specific patterns at the basal body complex in vertebrate ciliated epithelial cells.

High-magnification in vivo imaging of Xenopus embryos for cell and developmental biology.

Embryos of the frog Xenopus laevis are an ideal model system for in vivo imaging of dynamic biological processes, from the inner workings of individual cells to the reshaping of tissues during embryogenesis. Their externally developing embryos are more amenable to in vivo analysis than internally developing mammalian embryos, and the large size of the embryos make them particularly suitable for time-lapse analysis of tissue-level morphogenetic events. In addition, individual cells in Xenopus embryos are larger than those in other vertebrate models, making them ideal for imaging cell behavior and subcellular processes (e.

In vivo imaging reveals a role for Cdc42 in spindle positioning and planar orientation of cell divisions during vertebrate neural tube closure.

Specialization of the cell-division process is a common feature of developing embryos, but most studies on vertebrate cell division have focused on cells dividing in culture. Here, we used in vivo four-dimensional confocal microscopy to explore the role of Cdc42 in governing cell division in the developing neural epithelium of Xenopus laevis. We find that Cdc42 is crucial for stable positioning of the metaphase spindle in these cells, but was not required for spindle positioning in epidermal epithelial cells.

Developmental regulation of central spindle assembly and cytokinesis during vertebrate embryogenesis.

Mitosis and cytokinesis not only ensure the proper segregation of genetic information but also contribute importantly to morphogenesis in embryos. Cytokinesis is controlled by the central spindle, a microtubule-based structure containing numerous microtubule motors and microtubule-binding proteins, including PRC1. We show here that central spindle assembly and function differ dramatically between two related populations of epithelial cells in developing vertebrate embryos examined in vivo.

Whole-mount fluorescence immunocytochemistry on Xenopus embryos.

INTRODUCTIONImmunocytochemistry (ICC) is widely exploited in studying mammalian systems, but is underutilized among Xenopus developmental biologists. This stems, in part, from the relatively small number of Xenopus antibodies available for use in research. Common misconceptions about ICC in Xenopus embryos also prevail, discouraging researchers from trying the procedure.