Coordination of mitosis and morphogenesis: role of a prolonged G2 phase during chordate neurulation

Abstract

SUMMARYChordates undergo a characteristic morphogenetic process during neurulation to form a dorsal hollow neural tube. Neurulation begins with the formation of the neural plate and ends when the left epidermis and right epidermis overlying the neural tube fuse to close the neural fold. During these processes, mitosis and the various morphogenetic movements need to be coordinated. In this study, we investigated the epidermal cell cycle in Ciona intestinalis embryos in vivo using a fluorescent ubiquitination-based cell cycle indicator (Fucci). Epidermal cells of Ciona undergo 11 divisions as the embryos progress from fertilization to the tadpole larval stage. We detected a long G2 phase between the tenth and eleventh cell divisions, during which fusion of the left and right epidermis occurred. Characteristic cell shape change and actin filament regulation were observed during the G2 phase. CDC25 is probably a key regulator of the cell cycle progression of epidermal cells. Artificially shortening this G2 phase by overexpressing CDC25 caused precocious cell division before or during neural tube closure, thereby disrupting the characteristic morphogenetic movement. Delaying the precocious cell division by prolonging the S phase with aphidicolin ameliorated the effects of CDC25. These results suggest that the long interphase during the eleventh epidermal cell cycle is required for neurulation.

Cycling through developmental decisions: how cell cycle dynamics control pluripotency, differentiation and reprogramming

“…The timing of mitotic entry and duration of G2 phase, during which cells are exposed to differentiation cues, therefore impacts Notch-mediated lateral inhibition and, consequently, cell fate decisions. Studies in zebrafish (Bouldin and Kimelman, 2014), sea squirts (Ogura et al, 2011), frogs and flies (Davidson et al, 2009) reinforce this concept. Together, these studies show that although there are variations to the central theme, the mechanistic coupling of the cell cycle to cell fate decisions is a strong recurring biological theme in multipotent cells from diverse origins.…”

Tissue-specific and ubiquitous gene knockouts by TALEN electroporation provide new approaches to investigating gene function inCiona

“…The TALEN targeting sites were identified using TALE-NT software (Doyle et al, 2012) (https://tale-nt.cac.cornell.edu/). CiEpi1>mCherry and Venus expression cassettes (Ogura et al, 2011) were ligated into a SacI site upstream of the TALEN gene and promoter.…”

Cdc25 and the importance of G2control

“…Just as the neural tube is rolling up, the proliferating epidermal cells prolong their G 2 phase by regulating Cdc25. 42 If Cdc25 is overexpressed specifically in the epidermal cells, the G 2 phase is shortened, and the neural tube fails to close. 42 During normal neural tube morphogenesis, the epidermal cells elongate in an actin-dependent manner, and this may provide the force that closes the neural tube (Fig.…”

“…42,49 One note of caution, it is important not to use promoters that express the Fucci at high levels, or cells will not degrade the fluorescent indicators or faithfully report the state of the cell cycle. Even with this caveat, Fucci promises the ability to identify new instances where cells are held in G 2 in different animal systems at all stages of development and in all tissues.…”