Skip to main content
. Author manuscript; available in PMC: 2020 Nov 10.
Published in final edited form as: Cell Rep. 2020 Oct 27;33(4):108311. doi: 10.1016/j.celrep.2020.108311

Figure 4. sox2 Activation in the Absence of Wnt Signaling Results in Ectopic Spinal Cords in Transplanted Cells.

Figure 4.

(A) Wild-type-to-wild-type transplant (N = 16).

(B) HS:TCFΔC-to-wild-type transplant (N = 18).

(C) HS:sox2-to-wild-type transplant (N = 4).

(D–F) tbx16 MO-to-wild-type transplant (N = 35) (D–D”). (E–E”) HS.TCFΔC tbx16 MO-to-wild-type transplant (N = 43, 35 with ectopic spinal cords). (F–F”) HS: sox2 x HS.TCFΔC transplant (N = 17, all with ectopic spinal cords). All of the transplants were performed by injecting donor embryos with 2% fluorescein dextran (false colored magenta) and transferring donor cells to the margin of 30% epiboly wild-type host embryos. All of the transplants were heat shocked at 40°C for 30 min. The loss of tbx16 function causes donor cells that would normally form paraxial mesoderm to become fin mesenchyme (D’, blue arrowheads indicate the spinal cord; see also Video S1). Donor tbx16 morphant cells in which Wnt signaling has been inhibited can exit the tailbud into the paraxial mesoderm territory (E’, arrows), where they form an ectopic spinal cord with a neural canal (E”, arrowheads; see also Video S2). The same phenomenon occurs when sox2 is activated and Wnt signaling is inhibited, where transplanted cells leave the tailbud to form an ectopic spinal cord (F’, arrows) with a neural canal (F”, arrowheads; see also Video S3). (G–I) Ectopic spinal cords formed from the combined loss of tbx16 function and Wnt signaling have differentiated neurons (green) that form long axonal projections as revealed by the neurog1:mKate2 transgene (H, H’, arrowhead, compared to control G). See also Figure S2 for analysis of neurog1:mKate2 in whole embryos with loss of Wnt signaling and gain of Sox2 function. A model shows the normal progression of events as NMPs transition to paraxial mesoderm, as well as the conditions causing activation of the checkpoint (tbx16 loss of function) or checkpoint inhibited in which ectopic spinal cords form or when mesoderm formation is rescued (I). The genetic pathway shown in (I) is based on Figure 2 (Sox2 activation of tbxta and inhibition of tbx16), as well as previously published work showing a Tbxta/Wnt signaling autoregulatory loop (Martin and Kimelman, 2008), and the inhibition of tbxta and sox2 expression by Tbx16 (Bouldin et al., 2015). The solid lines indicate the known direct regulatory interactions.