Abstract
One of the most common cell shape changes driving morphogenesis in diverse animals is the constriction of the apical cell surface. Apical constriction depends on contraction of an actomyosin network in the apical cell cortex, but such actomyosin networks have been shown to undergo continual, conveyor belt-like contractions even before the shrinking of an apical surface begins. This finding suggests that apical constriction is not necessarily triggered by the contraction of actomyosin networks, but rather by unidentified, temporally-regulated mechanical links between actomyosin and junctions. Here, we used C. elegans gastrulation as a model to identify proteins that contribute to such linkage. We found that α-catenin and β-catenin initially failed to move centripetally with contracting cortical actomyosin networks, suggesting that linkage is regulated between cadherin-catenin complexes and actomyosin. We used a proteomic approach to identify AFD-1/afadin and transcriptomics to identify ZYX-1/zyxin as contributors to C. elegans gastrulation. We found that a zyxin family of LIM domain proteins have transcripts that become enriched in multiple cells just before they undergo apical constriction. Using a new, semi-automated image analysis tool, we found that AFD-1/afadin and ZYX-1/zyxin both contribute to cell-cell junctions’ centripetal movement in concert with contracting actomyosin networks. These results identify two key proteins as important for actomyosin networks to effectively pull cell-cell junctions inward during apical constriction. The transcriptional upregulation of zyxin/ZYX-1 in specific cells points to one way that developmental patterning spatiotemporally regulates cell biological mechanisms in vivo. Because afadin- and zyxin-family proteins contribute to membrane-cytoskeleton linkage in other systems, we anticipate that their roles in regulating apical constriction in this manner may be conserved.
Author summary Animals take shape during development in large part by the bending of tissues, and failures in this process are common causes of human birth defects. Such tissue bending is driven primarily by individual cells changing shape: in many examples, one side of a cell shrinks, pulling on junctions that connect the cell to neighboring cells. But the networks that drive one side of a cell to shrink are not always connected to junctions. As a result, focus has turned to understanding how connections between such networks and junctions are dynamically regulated to trigger cell shape change. We sought to identify genes that contribute to these critical connections. Here, we describe proteomic and transcriptomic methods that we used to identify two proteins that contribute to cell shape change. We developed a new image analysis tool and used it to reveal that loss of these two genes results in networks moving without efficiently pulling in junctions. Our results pinpoint two key genes whose products might contribute to dynamically connecting networks to junctions to trigger tissue shape changes in other organisms.
Competing Interest Statement
The authors have declared no competing interest.