Detailed analysis of chick optic fissure closure reveals Netrin-1 as an essential and conserved mediator of epithelial fusion during vertebrate embryogenesis

ABSTRACTEpithelial fusion underlies many vital organogenic processes during embryogenesis. Disruptions to these cause a significant number of human birth defects, including ocular coloboma. We provide robust spatial-temporal staging and unique anatomical detail of optic fissure closure (OFC) in the embryonic chick, including strong evidence for roles of apoptosis and epithelial remodelling. We performed complementary transcriptomic profiling and show that Netrin-1 (NTN1) is precisely expressed in the chick fissure margin at the fusion plate but is immediately downregulated after fusion. We further provide a combination of protein localisation and phenotypic evidence in chick, humans, mice and fish that Netrin-1 has an evolutionarily conserved and essential requirement for OFC, and is likely to have a major role in palate fusion. Our data reveal that NTN1 is a new locus for human coloboma and other multi-system developmental fusion defects, and that chick OFC is a powerful model for epithelial fusion research.

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Detailed analysis of chick optic fissure closure reveals Netrin-1 as an essential mediator of epithelial fusion

eLife ◽

10.7554/elife.43877 ◽

2019 ◽

Vol 8 ◽

Cited By ~ 9

Author(s):

Holly Hardy ◽

James GD Prendergast ◽

Aara Patel ◽

Sunit Dutta ◽

Violeta Trejo-Reveles ◽

...

Keyword(s):

Birth Defects ◽

Embryonic Chick ◽

Candidate Locus ◽

Essential Requirement ◽

Evolutionarily Conserved ◽

Protein Localisation ◽

Anatomical Detail ◽

Strong Candidate ◽

Epithelial Fusion ◽

Human Birth

Epithelial fusion underlies many vital organogenic processes during embryogenesis. Disruptions to these cause a significant number of human birth defects, including ocular coloboma. We provide robust spatial-temporal staging and unique anatomical detail of optic fissure closure (OFC) in the embryonic chick, including evidence for roles of apoptosis and epithelial remodelling. We performed complementary transcriptomic profiling and show that Netrin-1 (NTN1) is precisely expressed in the chick fissure margin during fusion but is immediately downregulated after fusion. We further provide a combination of protein localisation and phenotypic evidence in chick, humans, mice and zebrafish that Netrin-1 has an evolutionarily conserved and essential requirement for OFC, and is likely to have an important role in palate fusion. Our data suggest that NTN1 is a strong candidate locus for human coloboma and other multi-system developmental fusion defects, and show that chick OFC is a powerful model for epithelial fusion research.

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Human Birth Defects

Before We Are Born ◽

10.1016/b978-1-4377-2001-3.00019-8 ◽

2013 ◽

pp. 295-311

Keyword(s):

Birth Defects ◽

Human Birth

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A putative stem-loop structure in Drosophila crumbs is required for mRNA localisation in epithelia and germline cells

Journal of Cell Science ◽

10.1242/jcs.236497 ◽

2020 ◽

pp. jcs.236497

Author(s):

Srija Bhagavatula ◽

Elisabeth Knust

Keyword(s):

Epithelial Cells ◽

Transmembrane Protein ◽

Loop Structure ◽

Stem Loop ◽

Stem Loop Structure ◽

Evolutionarily Conserved ◽

Mrna Enrichment ◽

Egg Chambers ◽

Protein Localisation ◽

Localization Element

Crumbs (Crb) is an evolutionarily conserved transmembrane protein localised in the apical membrane of epithelial cells. Loss or mis-localisation of Crb is often associated with disruption of apico-basal cell polarity. crb mRNA is also apically enriched in epithelial cells, and, as shown here, accumulates in the oocyte of developing egg chambers. We narrowed down the Localization Element (LE) of crb mRNA to 47 nucleotides forming a putative stem-loop structure, suggesting to be recognised by Egalitarian (Egl). Mutations in conserved nucleotides abrogate apical transport. crb mRNA enrichment in the oocyte is affected in egl mutant egg chambers. A CRISPR based genomic deletion of the crb locus that includes the LE disrupts asymmetric crb mRNA localisation in epithelia and prevents its accumulation in the oocyte during early stages of oogenesis, but does not affect Crb protein localisation in embryonic and follicular epithelia. However, flies lacking the LE show ectopic Crb protein expression in the nurse cells. These data suggest an additional role of the Drosophila 3’-UTR in regulating translation in a tissue specific manner.

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