The Caenorhabditis elegans homolog of the Opitz syndrome gene, madd-2/Mid1, regulates anchor cell invasion during vulval development

Abstract

Mutations in the human Mid1 gene cause Opitz G/BBB syndrome, which is characterized by various midline closure defects. The Caenorhabditis elegans homolog of Mid1, madd-2, positively regulates signaling by the unc-40 Netrin receptor during the extension of muscle arms to the midline and in axon guidance and branching. During uterine development, a specialized cell called anchor cell (AC) breaches the basal laminae separating the uterus from the epidermis and invades the underlying vulval tissue. AC invasion is guided by an UNC-6 Netrin signal from the ventral nerve cord and an unknown guidance signal from the vulval cells. Using genetic epistasis analysis, we show that madd-2 regulates AC invasion downstream of or in parallel with the Netrin signaling pathway. Measurements of AC shape, polarity and dynamics indicate that MADD-2 prevents the formation of ectopic AC protrusions in the absence of guidance signals. We propose that MADD-2 represses the intrinsic invasive capacity of the AC, while the Netrin and vulval guidance cues locally overcome this inhibitory activity of MADD-2 to guide the AC ventrally into the vulval tissue. Therefore, developmental cell invasion depends on a precise balance between pro- and anti-invasive factors.

B-LINK: A Hemicentin, Plakin, and Integrin-Dependent Adhesion System that Links Tissues by Connecting Adjacent Basement Membranes

“…Notably, hemicentin did not accumulate intracellularly, indicating that integrin is not required for hemicentin secretion (n=10/10 animals observed; Figure 5A). Furthermore, hemicentin was not deposited inappropriately along the lateral membrane of the AC, which occurs when AC polarity is disrupted (Morf et al, 2013; Ziel et al, 2009). Increased levels of hemicentin, however, were found diffusely in the surrounding BM under the AC (Figure 5A, 5B and S5).…”

UNC-6 (netrin) stabilizes oscillatory clustering of the UNC-40 (DCC) receptor to orient polarity

“…Unlike other effectors of UNC-40, genetic interaction studies have suggested that MADD-2 does not function downstream of UNC-40, but instead acts upstream or as a cofactor to potentiate UNC-40’s activity in directing guidance responses (Alexander et al, 2010; Hao et al, 2010). Intriguingly, recent studies have shown that madd-2 is expressed in the AC and regulates AC invasion (Morf et al, 2013).…”

The Invading Anchor Cell Induces Lateral Membrane Constriction during Vulval Lumen Morphogenesis in C. elegans

“…In each panel, the yellow arrowhead points at the AC-VulF contact sites. (E) Intensity plots of LifeAct::GFP along the lateral VulF membranes were generated from yz-projections as shown in the inset, using a custom script described by (Morf et al, 2013) (see also materials and methods). The error bars indicate the standard deviations and the numbers in brackets the numbers of animals analyzed.…”

“…In each panel, the yellow arrowhead points at the AC-VulF contact sites. (J) Intensity plots of NMY-2::GFP staining along the basal VulF membranes were generated from xy-views as shown in the inset, using a custom script described by (Morf et al, 2013) undergoing apical and lateral constriction were traced using the cell profiler software package using a custom script (Carpenter et al, 2006). The basolateral membranes are shown in red and the apical membranes in blue.…”

“…Intensity plots of LifeAct::GFP or NMY-2::GFP along the lateral VulF membranes were generated using custom script as described (Morf et al, 2013). For each animal, the intensity in yz-axis projections of the lateral VulF membrane regions (outlined with a yellow dashed box in the example shown in the inset) or in xz-projections (blue dashed boxes) were divided into ten equal segments along the dorso-ventral axis.…”