Axis-inducing activities and cell fates of the zebrafish organizer

Abstract

We have investigated axis-inducing activities and cellular fates of the zebrafish organizer using a new method of transplantation that allows the transfer of both deep and superficial organizer tissues. Previous studies have demonstrated that the zebrafish embryonic shield possesses classically defined dorsal organizer activity. When we remove the morphologically defined embryonic shield, embryos recover and are completely normal by 24 hours post-fertilization. We find that removal of the morphological shield does not remove all goosecoid- and floating head-expressing cells, suggesting that the morphological shield does not comprise the entire organizer region. Complete removal of the embryonic shield and adjacent marginal tissue, however, leads to a loss of both prechordal plate and notochord. In addition, these embryos are cyclopean, show a significant loss of floor plate and primary motorneurons and display disrupted somite patterning. Motivated by apparent discrepancies in the literature we sought to test the axis-inducing activity of the embryonic shield. A previous study suggested that the shield is capable of only partial axis induction, specifically being unable to induce the most anterior neural tissues. Contrary to this study, we find shields can induce complete secondary axes when transplanted into host ventral germ-ring. In induced secondary axes donor tissue contributes to notochord, prechordal plate and floor plate. When explanted shields are divided into deep and superficial fragments and separately transplanted we find that deep tissue is able to induce the formation of ectopic axes with heads but lacking posterior tissues. We conclude that the deep tissue included in our transplants is important for proper head formation.

Multiple stable steady states of a reaction-diffusion model on zebrafish dorsal-ventral patterning

“…Organizer size. The system is robust with respect to the change of the organizer size, which is consistent with the biological experiments [7]. In our simulations, we assume that the organizer is located at the right end, just as the wild type case [13].…”

“…In [13], a nonlinear reaction-diffusion model on both three-dimensional and a simplified one-dimensional spatial domains was developed for computational analysis of BMP morphogen gradient formation in dorsal-ventral patterning of the zebrafish embryo. The model predicts that the dorsal organizer of the zebrafish embryo plays a key role in forming a stable non-homogeneous morphogen gradient, and the prediction agrees well with the existing biological experiments [7]. We briefly describe the model in the following paragraphs.…”

The tandem–random transition of cellular patterning: Roles of N-cadherin-based orientational cell adhesions in the development, maintenance, and degeneration of the nucleus pulposus

“…The involvement of N-cadherin in the notochord formation may also depend on the surrounding tissues because interactions between the notochord and surrounding tissues in uence their development (Placzek, 1995;Saude et al, 2000). For example, the neural tube and the notochord are known to in uence each other's development (Corallo et al, 2015;Stemple, 2005).…”

“…The anteroposteriorly elongated, rigid, and yet exible notochord is composed of cells cohered in a tandem fashion as rod-shaped tissue; it supports embryos' structural integrity and locomotion (Corallo et al, 2015;Stemple, 2005). In addition, the notochord is an organizer that secretes signals to orchestrate the development of many surrounding tissues (Placzek, 1995;Saude et al, 2000).…”

BMP Signaling: Lighting up the Way for Embryonic Dorsoventral Patterning

“…Waddington discovered that secondary tissues could also be induced by transplanting the primitive node of donor duck embryos to the epiblast of the host chick embryo ( Waddington, 1933 ; Waddington and Schmidt, 1933 ). About 60 years later, scientists Koshida S and Saude L found that the chicken Hensen’s node and the zebrafish shield induced formation of a secondary axes in zebrafish embryos ( Koshida et al, 1998 ; Saude et al, 2000 ). Contemporary, developmental biologists showed that transplanting the mouse node of a 7-days mouse embryo to the posterolateral side of the host also induced formation of a secondary axis ( Varlet et al, 1997 ; Koshida et al, 1998 ; Joubin and Stern, 1999 ).…”