Non-centrosomal epidermal microtubules act in parallel to LET-502/ROCK to promote C. elegans elongation

Abstract

There was an error in Development (2016Development ( ) 143, 160-173 (doi: 10.1242).The first name of the second author was spelled incorrectly. The online version has now been corrected. The authors apologise to readers for this mistake. C. elegans embryonic elongation is a morphogenetic event driven by actomyosin contractility and muscle-induced tension transmitted through hemidesmosomes. A role for the microtubule cytoskeleton has also been proposed, but its contribution remains poorly characterized. Here, we investigate the organization of the noncentrosomal microtubule arrays present in the epidermis and assess their function in elongation. We show that the microtubule regulators γ-tubulin and NOCA-1 are recruited to hemidesmosomes and adherens junctions early in elongation. Several parallel approaches suggest that microtubule nucleation occurs from these sites. Disrupting the epidermal microtubule array by overexpressing the microtubulesevering protein Spastin or by inhibiting the C. elegans ninein homolog NOCA-1 in the epidermis mildly affected elongation. However, microtubules were essential for elongation when hemidesmosomes or the activity of the Rho kinase LET-502/ROCK were partially compromised. Imaging of junctional components and genetic analyses suggest that epidermal microtubules function together with Rho kinase to promote the transport of E-cadherin to adherens junctions and myotactin to hemidesmosomes. Our results indicate that the role of LET-502 in junctional remodeling is likely to be independent of its established function as a myosin II activator, but requires a microtubule-dependent pathway involving the syntaxin SYX-5. Hence, we propose that non-centrosomal microtubules organized by epidermal junctions contribute to elongation by transporting junction remodeling factors, rather than having a mechanical role.

Noncentrosomal microtubules in C. elegans epithelia

“…In the embryonic epidermis, g-tubulin switches from a dotty centrosomal signal to a noncentrosomal location at the cell surface, along hemidesmosome-like junctions (which anchor epidermal cells to the extracellular matrix that separates them from the underlying muscles), or along cell-cell junctions (Fig. 1A-F) Quintin et al, 2016;Wang et al, 2015). In the embryonic intestine, g-tubulin and several proteins of the PCM (ZYG-9, TAC-1, AIR-1 and GIP-1, also known as CeGrip-1) re-localize in a two-step mechanism to the apical surface; these proteins subsequently decorate the intestinal lumen, coincidently with a nuclear movement from the cell center to its apex ( Fig.…”

“…While their functions have mainly been characterized in early embryos and neurons, at least TBA-2, TBA-4, TBA-7, TBB-2, TBB-6, and TBG-1 are known to be expressed in epithelia (Feldman and Priess, 2012;Fukushige et al, 1993;Hunt-Newbury et al, 2007;Quintin et al, 2016;Shaye and Greenwald, 2015;Wang et al, 2015).…”

“…Originally described in the zygote as a proxy for MT polymerization (Srayko et al, 2005), the plus-end binding protein EBP-2 has been observed is several epithelia, among which the epidermis (Green et al, 2011;Quintin et al, 2016;Wang et al, 2015) and the intestine .…”

“…One paper has addressed the role of the cytosolic CCT/TRiC chaperonin in the intestine (Saegusa et al, 2014); other chaperonins of the CCT and prefoldin families have been showed to affect MTs in the epidermis (Quintin et al, 2016).…”

“…The following fusion proteins with tubulin or MT-binding domains have been used: TBA-2::GFP (Quintin et al, 2016), VAB-10B(MTBD)::GFP (Kim et al, 2011), ensconsin-MTBD::3xGFP (Shaye and Greenwald, 2015), TBG-1::GFP and GIP-2::GFP (Feldman and Priess, 2012;Quintin et al, 2016;Wang et al, 2015). Tracking MT minus ends has mostly been achieved using TBG-1::GFP and GIP-2::GFP (Feldman and Priess, 2012;Quintin et al, 2016;Wang et al, 2015), and the 1TIP marker EBP-2::GFP has been used as a reporter of MT dynamics (Quintin et al, 2016;Shaye andGreenwald, 2015, Wang et al, 2015) which was initially developed in the early embryo by (Srayko et al, 2005).…”