Metazoan eggs have a specialized coat of extracellular matrix that aids in sperm-egg recognition. The coat is rapidly remodeled after fertilization to prevent polyspermy and establish a more permanent barrier to protect the developing embryo. In nematodes, this coat is called the vitelline layer, which is remodeled into the outermost layer of a rigid and impermeable eggshell. We have identified three key components of the vitelline layer structural scaffold - PERM-2, PERM-4 and CBD-1, the first such proteins to be described in the nematode C. elegans. CBD-1 tethered PERM-2 and PERM-4 to the nascent vitelline layer via two N-terminal chitin-binding domains. After fertilization, all three proteins redistributed from the zygote surface to the outer eggshell. Depletion of PERM-2 and PERM-4 from the scaffold led to a porous vitelline layer that permitted soluble factors to leak through the eggshell and resulted in embryonic death. In addition to its role in vitelline layer assembly, CBD-1 is also known to anchor a protein complex required for fertilization and egg activation (EGG-1-5/CHS-1/MBK-2). We found the PERM complex and EGG complex to be functionally independent, and structurally organized through distinct domains of CBD-1. CBD-1 is thus a multifaceted regulator that promotes distinct aspects of vitelline layer assembly and egg activation. In sum, our findings characterize the first vitelline layer components in nematodes, and provide a foundation through which to explore both conserved and species-specific strategies used by animals to build protective barriers following fertilization.

14Wnt5a-Ror signaling is a conserved pathway that regulates morphogenetic processes during vertebrate 15 development, but its downstream signaling events remain poorly understood. By conducting a large-scale 16 proteomic screen in mouse embryonic fibroblasts, we identified the E3 ubiquitin ligase Pdzrn3 as a new 17 regulatory target that is degraded upon pathway activation in a b-catenin-independent, ubiquitin-proteasome 18 system-dependent manner. We developed a flow cytometry-based reporter to monitor Pdzrn3 abundance and 19 delineated a signaling cascade involving Frizzled, Dishevelled, Casein kinase 1, and Glycogen synthase 20 kinase 3 that regulates Pdzrn3 stability. Genetic epistasis analysis suggests that Pdzrn3 degradation occurs 21 downstream of Dishevelled but independently of Kif26b, a previously identified Wnt5a-Ror-Dishevelled 22 signaling target. Further, we discovered that Pdzrn3 degradation requires Wnt5a-dependent phosphorylation of 23 three residues within its C-terminal LNX3H domain, which is conserved in other homologs and likely functions 24 as a Wnt5a-responsive domain. Collectively, this work establishes a new Wnt5a-Ror signaling cascade 25 involving Pdzrn3 phosphorylation and degradation.26 27

Wnt5a-Ror signaling is a conserved pathway that regulates morphogenetic processes during vertebrate development [R. T. Moon et al., Development 119, 97–111 (1993); I. Oishi et al., Genes Cells 8, 645–654 (2003)], but its downstream signaling events remain poorly understood. Through a large-scale proteomic screen in mouse embryonic fibroblasts, we identified the E3 ubiquitin ligase Pdzrn3 as a regulatory target of the Wnt5a-Ror pathway. Upon pathway activation, Pdzrn3 is degraded in a β-catenin–independent, ubiquitin-proteasome system–dependent manner. We developed a flow cytometry-based reporter to monitor Pdzrn3 abundance and delineated a signaling cascade involving Frizzled, Dishevelled, Casein kinase 1, and Glycogen synthase kinase 3 that regulates Pdzrn3 stability. Epistatically, Pdzrn3 is regulated independently of Kif26b, another Wnt5a-Ror effector. Wnt5a-dependent degradation of Pdzrn3 requires phosphorylation of three conserved amino acids within its C-terminal LNX3H domain [M. Flynn, O. Saha, P. Young, BMC Evol. Biol. 11, 235 (2011)], which acts as a bona fide Wnt5a-responsive element. Importantly, this phospho-dependent degradation is essential for Wnt5a-Ror modulation of cell migration. Collectively, this work establishes a Wnt5a-Ror cell morphogenetic cascade involving Pdzrn3 phosphorylation and degradation.

During cytokinesis, signals from the central spindle stimulate the accumulation of active RhoA-GTPase and thus contractile ring components at the equator, while the astral microtubules inhibit such components at the polar cortex. The DEPDC1 family protein LET-99 is required for furrow ingression in the absence of the central spindle signal, and for timely onset of furrowing even in the presence of the central spindle signal. Here we show that LET-99 works downstream or independently of RhoA-GTP and antagonizes branched F-actin and the Rac protein CED-10 to promote furrow initiation. This interaction with CED-10 is separable from LET-99s function in spindle positioning. We also characterize a new role for LET-99 in regulating cortical stability, where LET-99 acts in parallel with the actomyosin scaffolding protein anillin, but LET-99 does not antagonize CED-10 in this case. We propose that LET-99 acts in a pathway that inhibits the Rac CED-10 to promote the proper balance of branched versus linear F-actin for cytokinesis, and that LET-99 also regulates another factor that contributes to cortical stability.

Wnt5a‐Ror signaling is a conserved developmental pathway that regulates morphogenetic processes during vertebral embryonic development, and dysfunction of the pathway causes a number of human disorders, including Robinow syndrome. The mechanisms of Wnt5a‐Ror signaling remain poorly understood. Using a large‐scale proteomic screen, we identified the E3 ubiquitin ligase Pdzrn3 as a new regulatory target that is degraded upon pathway activation in a beta‐catenin independent, ubiquitin‐proteasome system dependent manner. Using this discovery, we developed a flow cytometry‐based reporter to monitor Pdzrn3 abundance and delineated a signaling cascade involving Frizzled, Dishevelled, Casein kinase 1, and Glycogen synthase kinase 3 that regulates Pdzrn3 degradation. Genetic epistasis analysis suggests that Pdzrn3 resides downstream of Dishevelled and independently of Kif26b, a previously identified Wnt5a‐Ror regulatory target. Further, we discovered that Pdzrn3 degradation requires Wnt5a‐dependent phosphorylation of its C‐terminal LNX3H domain, which is conserved in several Pdzrn3 homologs and likely functions as a novel Wnt5a‐responsive domain. Collectively, this work establishes a new Wnt5a‐Ror signaling cascade involving Pdzrn3 phosphorylation and degradation. Support or Funding Information NIH Grant 1R35GM119574