Figure 1

Axial Patterning Can Occur in the Absence of Yolk

(A–K) Explants of early embryonic blastomeres taken at the (A) 256-cell stage demonstrate elongation and mesendodermal induction visualized through expression of a (B–F) Tbx16::GFP reporter (n = 4/8; heterozygous in-cross) and (G–K) tbxta mRNA (n = 1 hpc 4/4; 2 hpc 5/6; 3 hpc 5/6; 5 hpc 6/8; 7 hpc 6/6).

(L and M) At the opposite pole to tbxta expression at 7 hpc, (L) bmp4 expression is observed at the opposing end of the aggregate to tbxta expression with (M) sox32 expression found in the center of some aggregates, but those without sox32 expression are able to elongate (n = 3/8; sox32 positive explants/assayed elongating explants).

(N) In the high bmp4 domain at 7 hpc, gata4 expression is observed (n = 8/9), with protocadherin8 (n = 8/9) expression more posteriorly and noto furthest posterior from the bmp4 expression domain (n = 7/9).

(O) Germ cell markers (O and O’) nanos and vasa are also observed coexpressed in cells within the core of the aggregates in the sox32-positive domain (n = 5/5) at 7 hpc.

Elongation is further quantified and shown to occur in a range of media in Figure S1. Time-lapse data of bright-field and Tbx16::GFP explants can be found in Video S1. Slice views, 3D views and surface renderings of in situ HCR data are available in Video S2. n = expression observed/total imaged. Scale bars represent 50 μm (A–K’) and 70 μm (L–O’).