Evolutionary modification of AGS protein contributes to formation of micromeres in sea urchins

Abstract

Evolution is proposed to result, in part, from acquisition of new developmental programs. One such example is the appearance of the micromeres in a sea urchin that form by an asymmetric cell division at the 4 th embryonic cleavage and function as a major signaling center in the embryo. Micromeres are not present in other echinoderms and thus are considered as a derived feature, yet its acquisition mechanism is unknown. Here, we report that the polarity factor AGS and its associated proteins are responsible for micromere formation. Evolutionary modifications of AGS protein seem to have provided the cortical recruitment and binding of AGS to the vegetal cortex, contributing to formation of micromeres in the sea urchins. Indeed, introduction of sea urchin AGS into the sea star embryo induces asymmetric cell divisions, suggesting that the molecular evolution of AGS protein is key in the transition of echinoderms to micromere formation and the current developmental style of sea urchins not seen in other echinoderms.

Evidence for BMP‐mediated specification of primordial germ cells in an indirect‐developing hemichordate

“…In addition to the aforementioned mechanisms, the enrichment of sea urchin Vasa is coupled to asymmetric cell division that results from the recruitment of AGS, a polarity factor, to the vegetal cortex (Poon et al, 2019). It has been postulated that acquisition of an additional GoLoco motif in the C‐terminus of the sea urchin AGS is important for the vegetal accumulation of the AGS‐Vasa complex (Poon et al, 2019). Using the sea urchin AGS sequence as a query, we identified a partial ags transcript in our P. flava transcriptome data.…”

A tumor suppressor Retinoblastoma1 is essential for embryonic development in the sea urchin

“…The exact location of each antigen sequence within SpRb1 is indicated in Table S3. Immunoblot was performed as described previously . Briefly, 2 μl each of embryonic lysate made from Day 2 embryos was run on a 10% polyacrylamide gel (Lonza, Rockland, ME) and transferred to nitrocellulose membranes for immunoblotting with rabbit polyclonal SpRb1 antibody #1–3 each or with mouse monoclonal β‐actin antibody (Cell Signaling Technology, #3700) at 1:2000 followed by HRP‐conjugated anti‐rabbit (Cell Signaling Technology, #7047) or anti‐mouse secondary antibody (Cell Signaling Technology, #7076), respectively.…”

“…Immunoblot was performed as described previously. 33 Briefly, 2 μl each of embryonic lysate made from Day 2 embryos was run on a 10% polyacrylamide gel (Lonza, Rockland, ME) and transferred to nitrocellulose membranes for immunoblotting with rabbit polyclonal SpRb1 antibody #1-3 each or with mouse monoclonal β-actin antibody (Cell Signaling Technology, #3700) at 1:2000 followed by HRP-conjugated anti-rabbit (Cell Signaling Technology, #7047) or anti-mouse secondary antibody (Cell Signaling Technology, #7076), respectively. The reacted proteins were detected by incubation in a chemiluminescence solution (1.25 mM luminol, 68 μM coumeric acid, 0.0093% hydrogen peroxide and 0.1 M Tris pH 8.6) for 1-10 minutes, exposed to film and developed.…”

Principles and mechanisms of asymmetric cell division

“…The polarity factor AGS is both necessary and sufficient to establish this physical and molecular ACD. Sea urchin AGS contains three GoLoco motifs, whereas sea star AGS lacks GoLoco motif #1, and it was recently shown that expressing sea urchin AGS in sea star embryos is sufficient to induce physical ACDs (Poon et al, 2019). It has also been shown that the core cortical force-generating machinery responsible for such cortical pulling forces is evolutionarily conserved and contains the Dynein-Dynactin complex, NuMA (Lin5 in C. elegans; Mud in Drosophila) and the Gαi complex (GOA-1, GPA-16 in C. elegans;…”