hoxb genes determine the timing of cell ingression by regulating cell surface fluctuations during zebrafish gastrulation

During embryonic development, cell behaviors need to be tightly regulated in time and space. Yet, how the temporal and spatial regulations of cell behaviors are interconnected during embryonic development remains elusive. To address this, we turned to zebrafish gastrulation, the process where dynamic cell behaviors generate the three principal germ layers of the early embryo. Here, we show that hoxb cluster genes are expressed in a temporally collinear manner at the blastoderm margin of the embryo to regulate the timing of mesoderm and endoderm (mesendoderm) cell ingression. Under- or over-expression of hoxb genes perturb the timing of mesendoderm cell ingression and, consequently, the positioning of these cells along the forming anterior-posterior body axis. Finally, we found that hoxb genes control the timing of mesendoderm ingression by regulating cell surface fluctuations. Thus, hoxb genes interconnect the temporal and spatial pattern of cell behavior in the early embryo by controlling cell surface fluctuations. HighlightsO_LIhoxb gene expression shows temporal collinearity at the blastoderm margin during zebrafish gastrulation. C_LIO_LITemporal collinear expression of hoxb genes at the blastoderm margin regulates the timing of cell ingression and delineates spatial collinearity after gastrulation. C_LIO_LIhoxb genes regulate cell surface fluctuations and bleb formation at the blastoderm margin during cell ingression C_LI Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=149 SRC="FIGDIR/small/579056v1_ufig1.gif" ALT="Figure 1"> View larger version (37K): org.highwire.dtl.DTLVardef@3a8517org.highwire.dtl.DTLVardef@1f7bda3org.highwire.dtl.DTLVardef@1c325a6org.highwire.dtl.DTLVardef@dce24d_HPS_FORMAT_FIGEXP M_FIG C_FIG hoxb genes are expressed at the blastoderm margin in a temporally collinear manner and determine the timing of mesendoderm ingression by triggering dynamic cell surface fluctuations and cell blebbing. This results in a spatial collinearity of mesendoderm cell positioning along the anterior-posterior extent of the forming body axis with early ingressing cells being positioned more anteriorly than late ingressing cells.