[
International Worm Meeting,
2021]
Apico-basolateral polarization is essential for epithelial cells to function as selective barriers and transporters and to provide mechanical resiliency to organs. Different epithelia use divergent mechanisms to establish polarity, which are only beginning to be understood. Here, we use the C. elegans embryonic intestine to investigate how epithelial cells establish apico-basolateral polarity in vivo. PAR-3 was previously identified as the most upstream polarity regulator in this organ (Achilleos et al 2010), but worms arrested in embryonic stages due to the essential role of PAR-3 in other tissues, precluding study of the role of intestinal PAR-3 for later developmental stages. Therefore, we depleted PAR-3 specifically from the embryonic intestine (PAR-3gut(-)) without affecting the function of PAR-3 in other tissues. PAR-3gut(-) worms all arrested at the L1 larval stage, with edematous intestines that lacked continuous lumens. Consistent with prior work, we found that PAR-3 is required for the localization of the apical kinase, PKC-3, in the intestine. However, proteins associated with the apical actin brush border still localize in discreet patches in PAR-3gut(-) embryos. Adherens junction proteins (HMR-1, AFD-1) organize into rings in PAR-3gut(-) embryonic intestines, and the septate-like junctional protein, DLG-1, formed similar rings slightly later in embryogenesis. Junctional proteins often encircled the actin-associated patches, indicating that some aspects of apical-basolateral polarity are established in the absence of PAR-3. Additionally, while PAR-3 is required for the localization of the basolateral protein, LGL-1, the basolateral protein, LET-413/Scribble is still excluded from specific regions of the cell membrane in PAR-3gut(-) intestines. Together, these data are consistent with the existence of a PAR-3 independent apical-basolateral establishment pathway. In other tissues, adherens junction proteins play upstream roles in apico-basolateral polarity establishment. To determine if junctional proteins act in parallel with PAR-3, we are currently depleting adherens junction proteins specifically from the intestine alone or in combination with PAR-3 depletion. While aspects of apico-basolateral polarity are established in PAR-3gut(-) worms, a continuous apical surface is never established, suggesting that PAR-3 is required for coordinating polarity establishment across the intestinal tissue.