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Fig. 8. Alternative deployment of the micromere-PMC GRN by NSM cells.
(A) An expanded view of the PMC GRN [modified, with permission, from
Oliveri et al. (Oliveri et al.,
2008)]. Many regulatory components of the micromere-PMC GRN are
normally deployed in NSM cells (black ovals). One key regulator not expressed
by these cells is alx1 (dark blue box). alx1 controls a
subcircuit that activates biomineralization and morphoregulatory genes via
intermediaries such as dri, foxB (light blue boxes) and
snail (not shown). (B-D) Ectopic deployment of alx1
during NSM transfating (L. variegatus). (B) An embryo at the
mesenchyme blastula stage. alx1 mRNA expression (dark purple) is
restricted to PMCs. (C) A mesenchyme blastula stage embryo immediately after
the microsurgical removal of PMCs. (D) An embryo 6 hours after the
microsurgical removal of PMCs. alx1 is expressed ectopically (dark
purple) by NSM cells at the tip of the archenteron. Activation of
alx1 in NSM cells occurs by a novel, pmar1-independent
mechanism. (E) Expression of alx1 is sufficient to trigger NSM
transfating. Co-injection of alx1 mRNA and a lineage tracer (green
nuclear label) into one macromere at the 16-cell stage induces descendants of
the labeled cell to adopt the PMC fate, as shown by immunostaining using a
monoclonal antibody that recognizes MSP130 proteins, a family of PMC-specific
cell surface proteins (red). White arrows mark transfated cells. Figure
modified, with permission, from Ettensohn et al.
(Ettensohn et al., 2007).
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