~1000 cells

Sea Urchin

Primary Mesenchyme = PMC = skeletogenic mesenchymeSecondary Mesenchyme = Non-Skeletal Mesoderm = NSMLarval also called Easel stage (כן)Blastula before invagination of endoderm = mesenchyme blastula stage0

Sea Urchin

Figure 8.13 The Micromere Regulatory Network Proposed byDavidson and Colleagues (2002)

hh hh hh hh Two morphogens/ligands/organizers in adjacent cells

NoActive

The embryoNow has twoAdjacent organizersWhich release a

Morphogen

From syncitium withGradient of 1 (or 2)Morphogens, to seriesOf segments, each

With 2 morphogens

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Hedgehog signaling pathway

Walton, KD et al. (2009) Hh signaling specifies sea urchin mesoderm

In situ –Shh

Walton, KD et al. (2009) Hh signaling specifies sea urchin mesoderm

Morpholino oligos

(MASOs:morpholino

antisenseoligos)

Walton, KD et al. (2009) Hh signaling specifies sea urchin mesoderm

Walton, KD et al. (2009) Hh signaling specifies sea urchin mesoderm

Walton, KD et al. (2009) Hh signaling specifies sea urchin mesoderm

Walton, KD et al. (2009) Hh signaling specifies sea urchin mesoderm

Walton, KD et al. (2009) Hh signaling specifies sea urchin mesoderm

Walton, KD et al. (2009) Hh signaling specifies sea urchin mesoderm

Walton, KD et al. (2009) Hh signaling specifies sea urchin mesoderm

Sea Urchin

Walton, KD et al. (2009) Hh signaling specifies sea urchin mesoderm

Walton, KD et al. (2009) Hh signaling specifies sea urchin mesoderm

Walton, KD et al. (2009) Hh signaling specifies sea urchin mesoderm