[
International Worm Meeting,
2019]
Polarization of epithelial cells into apical and basolateral domains is essential for the functioning of epithelia as selectively permeable barriers. The basolateral Scribble group proteins (Scrib, Lgl, Dlg) were originally identified as tumor suppressors in D. melanogaster and were later shown to play key roles in the establishment and maintenance of polarity in a broad range of cell types. In addition to promoting basolateral identity, Scribble group proteins regulate diverse processes including tissue growth, differentiation and directed cell migration, and therefore are major regulators of tissue development and homeostasis. In C. elegans, loss of LET-413/Scrib and DLG-1/Dlg results in defects in epithelial polarization and junction formation during embryonic development, resulting in embryonic lethality. However, their importance in larval epithelia is less well understood. To study the role of LET-413 in larval epithelia, we generated an allele that allows inducible protein degradation using the auxin-inducible system recently developed for C. elegans (1). We find that ubiquitous degradation of LET-413 in larval tissues results in a developmental arrest. Tissue-specific degradation of LET-413 in the larval intestine does not cause defects in development. In contrast, degradation of LET-413 in the seam cells and hypodermis mimics the developmental arrest seen upon ubiquitous LET-413 degradation. Live-cell imaging of seam cells shows a severe effect on outgrowth and reattachment following the L1 asymmetric division. In addition, we observed that loss of LET-413 results in punctate and discontinuous localization pattern of DLG-1, similar to previous observations in C. elegans embryos. We are currently following the effects of LET-413 inactivation on cell recognition and migration pathways to understand the outgrowth defects of the seam cells. (1) Zhang L, Ward JD, Cheng Z, Dernburg AF. Development. 2015 Dec 15;142(24):4374-84.
Pires, Helena, Van den Heuvel, Sander, Boxem, Mike, de Groot, Hanna, Riga, Amalia, Cravo, Janine
[
International Worm Meeting,
2019]
Cell-cell contacts are critical for epithelial polarity, proliferation control, and tissue organization. While cell junctions contribute to contact inhibition and cell division orientation in some epithelia, it remains unclear whether and how such roles exist in other systems. Here, we investigate the contribution of junctional contacts in the reproducible pattern of C. elegans seam cell divisions. Seam cells reside within two lateral epithelia, are connected through apical junctions, show apical-basal as well as anterior-posterior polarity, and undergo asymmetric cell divisions dependent on Wnt/beta-catenin asymmetry signaling. We sought to specifically disrupt seam-cell junctions, in order to investigate whether these contacts guide anterior-posterior tissue polarity and cell proliferation control. Hereto, we used tissue-specific gene knockout and protein degradation of the HMR-1 E-cadherin homolog. This resulted in gaps in the seam cell row, and occasionally fully detached seam cells at later larval stages. The detached cells were most prominent near the head and tail. They showed apparently normal division timing and occasional defects in spindle orientation. However, based on APR-1 localization and cell fusion events, the detached cells showed frequent reversal or loss of Wnt/beta-catenin asymmetry and cell fate, in later development. Combined inactivation of HMR-1 and an additional junctional component, SAX-7, resulted in full seam cell detachment in early development. We will use this double knockout to further characterize the contribution of adhesive contacts and cellular shape in the control of tissue polarity and proliferation, and will present our latest results at the meeting.