How to be at the right place at the right time: The importance of spindle positioning in embryos

Abstract

SUMMARYSpindle positioning is an imperative cellular process that regulates a number of different developmental events throughout embryogenesis. The spindle must be properly positioned in embryos not only for the segregation of chromosomes, but also to segregate developmental determinants into different daughter blastomeres. In this review, the role of spindle positioning is explored in several different developmental model systems, which have revealed the diversity of factors that regulate spindle positioning. The C. elegans embryo, the Drosophila neuroblast, and ascidian embryos have all been utilized for the study of polarity-dependent spindle positioning, and exploration of the proteins that are required for asymmetric cell division. Work in the sea urchin embryo has examined the influence of cell shape and factors that affect secondary furrow formation. The issue of size scaling in extremely large cells, as well as the requirement for spindle positioning in developmental fate decisions in vertebrates, has been addressed by work in the Xenopus embryo. Further work in mouse oocytes has examined the roles of actin and myosin in spindle positioning. The data generated from these model organisms have made unique contributions to our knowledge of spindle positioning. Future work will address how all of these different factors work together to regulate the position of the spindle. Spindles play an important role in embryos as their location within the cell has a significant impact on subsequent development.

Animal Female Meiosis: The Challenges of Eliminating Centrosomes

“…The defined orientation of the spindle is a structural basis for cell differentiation in early embryos. Hence, centrosomes need to establish interactions of the spindle with the cortex and the plasma membrane via their cytoplasmic (“astral”) microtubules [ 35 , 36 , 37 ]. Additionally, spindle formation ought to be extremely fast during the short cell cycles in early embryos.…”

Physical association between a novel plasma-membrane structure and centrosome orients cell division

“…The orientation of the mitotic division axis has been proposed to control tissue morphogenesis as well as cell fate determination, thus playing an important role in shaping embryonic forms ( Lu and Johnston, 2013 ; Moorhouse and Burgess, 2014 ; Siller and Doe, 2009 ). The mechanism determining the orientation of the mitotic spindle has been extensively studied in both cultured and embryonic cells and precise molecular processes are well understood ( Bell et al, 2015 ; Cao et al, 2010 ; Delaval et al, 2011 ; Kiyomitsu and Cheeseman, 2012 ; Woolner and Papalopulu, 2012 ; Zheng et al, 2010 ).…”

Mechanisms of spindle assembly and size control

“…Even though astral MTs were shown to be important for spindle orientation and asymmetric cell division [Siller and Doe, 2009], they are absent or not long enough to extend from pole to cell membrane in cells without centrosomes or in very large embryonic cells, respectively. In such cases, other players, such as for instance acentriolar MT organising centres or the actin network, function to position the spindle [Moorhouse and Burgess, 2014; Bennabi et al., 2016; Mogessie et al., 2018]. Bundles of MTs, called k‐fibres, connect the spindle to the chromosomes through a macromolecular complex termed the kinetochore [Cheeseman and Desai, 2008], which assembles at the centromere of each sister chromatid at the onset of mitosis.…”