Khor JM , Ettensohn CA .

Figure 1. Molecular phylogeny of Alx proteins (adapted from McGonnell et al., 2011; Koga et al., 2016). Branch lengths are arbitrary. Sk, Saccoglossus kowalevskii (acorn worm); Lv, Lytechinus variegatus (euechinoid sea urchin); Hp, Hemicentrotus pulcherrimus (euechinoid sea urchin); Sp, Strongylocentrotus purpuratus (euechinoid sea urchin); Mr, Metacrinus rotundus (sea lily); Ak, Amphipholis kochii (brittle star); Pm, Patiria miniata (sea star); Ppc, Patiria pectinifera (sea star); Bf, Branchiostoma floridae (lancelet); Dr, Danio rerio (zebrafish); Xt, Xenopus tropicalis (frog); Ac, Anolis carolinensis (lizard); Hs, Homo sapiens (human); Mm, Mus musculus (mouse).

Figure 2. Activation of Alx1 in euechinoids (S. purpuratus) and regulatory inputs into primary mesenchyme cell (PMC) effector genes. Only a small number of more than 420 effector genes differentially expressed in PMCs (Rafiq et al., 2014) is shown here. A large subset of effector genes receives regulatory inputs from both Ets1 and Alx1 (Rafiq et al., 2014). Positive regulatory inputs by Ets1 and Alx1 into msp130, sm50, and vegf-Ig-10 are described in (Oliveri et al., 2008). Direct targets of the sea urchin Alx1 (Khor et al., 2019) define a genetic subcircuit that impinges on almost all aspect of PMC morphogenesis, including directional cell migration, extracellular matrix (ECM) remodeling, cell-cell fusion, and biomineralization. Dashed arrows indicate interactions that may be indirect. For additional information regarding the developmental functions of the specific effector genes shown here, see Shashikant et al. (2018) and references therein.

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