Reciprocal EGFR signaling in the anchor cell ensures precise inter-organ connection during Caenorhabditis elegans vulval morphogenesis

The C. elegans anchor cell: A model to elucidate mechanisms underlying invasion through basement membrane

Cell invasion through basement membrane barriers is crucial during many developmental processes and in immune surveillance. Dysregulation of invasion also drives the pathology of numerous human diseases, such as metastasis and inflammatory disorders. Cell invasion involves dynamic interactions between the invading cell, basement membrane, and neighboring tissues. Owing to this complexity, cell invasion is challenging to study in vivo, which has hampered the understanding of mechanisms controlling invasion. Caenorhabditis elegans anchor cell invasion is a powerful in vivo model where subcellular imaging of cell-basement membrane interactions can be combined with genetic, genomic, and single-cell molecular perturbation studies. In this review, we outline insights gained by studying anchor cell invasion, which span transcriptional networks, translational regulation, secretory apparatus expansion, dynamic and adaptable protrusions that breach and clear basement membrane, and a complex, localized metabolic network that fuels invasion. Together, investigation of anchor cell invasion is building a comprehensive understanding of the mechanisms that underlie invasion, which we expect will ultimately facilitate better therapeutic strategies to control cell invasive activity in human disease.

Genetic characterization of C. elegans TMED genes

BACKGROUND

p24/transmembrane Emp24 domain (TMED) proteins are a set of evolutionarily conserved, single pass transmembrane proteins that have been shown to facilitate protein secretion and selection of cargo proteins to transport vesicles in the cellular secretion pathway. However, their functions in animal development are incompletely understood.

RESULTS

The C. elegans genome encodes eight identified TMED genes, with at least one member from each defined subfamily (α, β, γ, δ). TMED gene mutants exhibit a shared set of defects in embryonic viability, animal movement, and vulval morphology. Two γ subfamily genes, tmed-1 and tmed-3, exhibit the ability to compensate for each other, as defects in movement and vulva morphology are only apparent in double mutants. TMED mutants also exhibit a delay in breakdown of basement membrane during vulva development.

CONCLUSIONS

The results establish a genetic and experimental framework for the study of TMED gene function in C. elegans, and argue that a functional protein from each subfamily is important for a shared set of developmental processes. A specific function for TMED genes is to facilitate breakdown of the basement membrane between the somatic gonad and vulval epithelial cells, suggesting a role for TMED proteins in tissue reorganization during animal development.

Post-embryonic endogenous expression and localization of LET-60/Ras in C. elegans

Ras GTPases regulate many developmental and physiological processes and mutations in Ras are associated with numerous human cancers. Here, we report the function, levels, and localization of an N-terminal knock-in of mNeonGreen (mNG) into C. elegans LET-60 /Ras. mNG:: LET-60 interferes with some but not all LET-60 /Ras functions. mNG:: LET-60 is broadly present in tissues, found at different levels in cells, and concentrates in distinct subcellular compartments, including the nucleolus, nucleus, intracellular region, and plasma membrane. These results suggest that mNG:: LET-60 can be a useful tool for determining LET-60 levels and localization once its functionality in a developmental or physiological process is established.

Differential production rates of cytosolic and transmembrane GFP reporters in C. elegans L3 larval uterine cells

Transgene driven protein expression is an important tool for investigating developmental mechanisms in C. elegans . Here, we have assessed protein production rates and levels in L3 larval uterine cells (UCs). Using ubiquitous promoter driven cytosolic and transmembrane tethered GFP, fluorescence recovery after photobleaching, and quantitative fluorescence analysis, we reveal that cytosolic GFP is produced at an ~two-fold higher rate than transmembrane tethered GFP and accumulates at ~five-fold higher levels in UCs. We also provide evidence that cytosolic GFP in the anchor cell, a specialized UC that mediates uterine-vulval connection, is more rapidly degraded through an autophagy-independent mechanism.

Won't You be My Neighbor: How Epithelial Cells Connect Together to Build Global Tissue Polarity

Epithelial tissues form continuous barriers to protect against external environments. Within these tissues, epithelial cells build environment-facing apical membranes, junction complexes that anchor neighbors together, and basolateral surfaces that face other cells. Critically, to form a continuous apical barrier, neighboring epithelial cells must align their apico-basolateral axes to create global polarity along the entire tissue. Here, we will review mechanisms of global tissue-level polarity establishment, with a focus on how neighboring epithelial cells of different origins align their apical surfaces. Epithelial cells with different developmental origins and/or that polarize at different times and places must align their respective apico-basolateral axes. Connecting different epithelial tissues into continuous sheets or tubes, termed epithelial fusion, has been most extensively studied in cases where neighboring cells initially dock at an apical-to-apical interface. However, epithelial cells can also meet basal-to-basal, posing several challenges for apical continuity. Pre-existing basement membrane between the tissues must be remodeled and/or removed, the cells involved in docking are specialized, and new cell-cell adhesions are formed. Each of these challenges can involve changes to apico-basolateral polarity of epithelial cells. This minireview highlights several in vivo examples of basal docking and how apico-basolateral polarity changes during epithelial fusion. Understanding the specific molecular mechanisms of basal docking is an area ripe for further exploration that will shed light on complex morphogenetic events that sculpt developing organisms and on the cellular mechanisms that can go awry during diseases involving the formation of cysts, fistulas, atresias, and metastases.

Tissue-specific inhibition of protein sumoylation uncovers diverse SUMO functions during C. elegans vulval development

The sumoylation (SUMO) pathway is involved in a variety of processes during C. elegans development, such as gonadal and vulval fate specification, cell cycle progression and maintenance of chromosome structure. The ubiquitous expression and pleiotropic effects have made it difficult to dissect the tissue-specific functions of the SUMO pathway and identify its target proteins. To overcome these challenges, we have established tools to block protein sumoylation and degrade sumoylated target proteins in a tissue-specific and temporally controlled manner. We employed the auxin-inducible protein degradation system (AID) to down-regulate the SUMO E3 ligase GEI-17 or the SUMO ortholog SMO-1, either in the vulval precursor cells (VPCs) or in the gonadal anchor cell (AC). Our results indicate that the SUMO pathway acts in multiple tissues to control different aspects of vulval development, such as AC positioning, basement membrane (BM) breaching, VPC fate specification and morphogenesis. Inhibition of protein sumoylation in the VPCs resulted in abnormal toroid formation and ectopic cell fusions during vulval morphogenesis. In particular, sumoylation of the ETS transcription factor LIN-1 at K169 is necessary for the proper contraction of the ventral vulA toroids. Thus, the SUMO pathway plays several distinct roles throughout vulval development.

Many proteins are chemically modified after they have been synthesized. In particular, conjugation with the Small Ubiquitin-like Modifier (SUMO) regulates the functions and activities of a large number of proteins in animal and plant cells.

Here, we have used the Nematode Caenorhabditis elegans to study the various effects of SUMO protein modification on organ development. By applying a tissue-specific protein degradation system, we could selectively block the SUMO pathway in different tissues of the animals. We focused on the development of the egg-laying organ as a model, and found that the SUMO pathway acts in multiple tissues to regulate distinct cellular functions. Finally, we show that SUMO modification of one transcription factor, called LIN-1, is necessary for the proper morphogenesis of the organ. Our results indicate that the manifold effects of the SUMO pathway can be attributed to the combined action of a distinct number of SUMO modified proteins acting in different cell types.

Identifying the Caenorhabditis elegans vulval transcriptome

Development of the Caenorhabditis elegans vulva is a classic model of organogenesis. This system, which starts with 6 equipotent cells, encompasses diverse types of developmental event, including developmental competence, multiple signaling events to control precise and faithful patterning of three cell fates, execution and proliferation of specific cell lineages, and a series of sophisticated morphogenetic events. Early events have been subjected to extensive mutational and genetic investigations and later events to cell biological analyses. We infer the existence of dramatically changing profiles of gene expression that accompanies the observed changes in development. Yet, except from serendipitous discovery of several transcription factors expressed in dynamic patterns in vulval lineages, our knowledge of the transcriptomic landscape during vulval development is minimal. This study describes the composition of a vulva-specific transcriptome. We used tissue-specific harvesting of mRNAs via immunoprecipitation of epitope-tagged poly(A) binding protein, PAB-1, heterologously expressed by a promoter known to express GFP in vulval cells throughout their development. The identified transcriptome was small but tightly interconnected. From this data set, we identified several genes with identified functions in development of the vulva and validated more with promoter-GFP reporters of expression. For one target, lag-1, promoter-GFP expression was limited but a fluorescent tag of the endogenous protein revealed extensive expression. Thus, we have identified a transcriptome of C. elegans vulval lineages as a launching pad for exploration of functions of these genes in organogenesis.