Search

L-fucose, a monosaccharide widely distributed in eukaryotes and certain bacteria, is a determinant of many functional glycans that play central roles in numerous biological processes. The molecular mechanism, however, by which fucosylation mediates these processes remains largely elusive. To study how changes in fucosylation impact embryonic development, we up-regulated N-linked fucosylation via over-expression of a key GDP-Fucose transporter, Slc35c1, in zebrafish. We show that Slc35c1 overexpression causes elevated N-linked fucosylation and disrupts embryonic patterning in a transporter activity dependent manner. We demonstrate that patterning defects associated with enhanced N-linked fucosylation are due to diminished canonical Wnt signaling. Chimeric analyses demonstrate that elevated Slc35c1 expression in receiving cells decreases the signaling range of Wnt8a during zebrafish embryogenesis. Moreover, we provide biochemical evidence that this decrease is associated with reduced Wnt8 ligand and elevated Lrp6 coreceptor, which we show are both substrates for N-linked fucosylation in zebrafish embryos. Strikingly, slc35c1 expression is regulated by canonical Wnt signaling. These results suggest that Wnt limits its own signaling activity in part via up-regulation of a transporter, slc35c1 that promotes terminal fucosylation and thereby limits Wnt activity.

Cells that produce internal organs move into the interior of the embryo during gastrulation. Somatic cell gastrulation movements are regulated by transcription factors that also control cell fate, ensuring that cell identity and position are coupled. By contrast, primordial germ cells (PGCs) in many species are transcriptionally quiescent, suggesting that they use alternative strategies to internalize. We show that C. elegans PGCs adhere to internal endodermal cells, which undergo morphogenetic movements that pull the PGCs into the embryo. We show that HMR-1/E-cadherin is enriched in PGCs, that HMR-1 is required for PGC internalization and PGC-endoderm adhesion, and that HMR-1 enrichment in PGCs is mediated by the hmr-1 3′ untranslated region. Our findings demonstrate the novel strategy that quiescent PGCs use to internalize during gastrulation, and identify a morphogenetic role for the evolutionarily conserved association between PGCs and endoderm.

We identified three zebrafish mutants with defects in biliary development. One of these mutants, pekin ( pn ), also demonstrated generalized hypopigmentation and other defects, including disruption of retinal cell layers, lack of zymogen granules in the pancreas, and dilated Golgi in intestinal epithelial cells. Bile duct cells in pn demonstrated an accumulation of electron dense bodies. We determined that the causative defect in pn was a splice site mutation in the atp6ap2 gene that leads to an inframe stop codon. atp6ap2 encodes a subunit of the vacuolar H + -ATPase (V-H + -ATPase), which modulates pH in intracellular compartments. The Atp6ap2 subunit has also been shown to function as an intracellular renin receptor that stimulates fibrogenesis. Here we show that mutants and morphants involving other V-H + -ATPase subunits also demonstrated developmental biliary defects, but did not demonstrate the inhibition of fibrogenic genes observed in pn . The defects in pn are reminiscent of those we and others have observed in class C VPS (vacuolar protein sorting) family mutants and morphants, and we report here that knockdown of atp6ap2 and vps33b had an additive negative effect on biliary development. Our findings suggest that pathways which are important in modulating intracompartmental pH lead to defects in digestive organ development, and support previous studies demonstrating the importance of intracellular sorting pathways in biliary development.