aura/mid1ip1L regulates the cytoskeleton at the zebrafish egg-to-embryo transition

Abstract

Embryos from females homozygous for a recessive maternal-effect mutation in the gene aura exhibit defects including reduced cortical integrity, defective cortical granule (CG) release upon egg activation, failure to complete cytokinesis, and abnormal cell wound healing. Subcellular analysis shows that the cytokinesis defects observed in aura mutants are associated with aberrant cytoskeletal reorganization during furrow maturation, including abnormal F-actin enrichment and microtubule reorganization. Cortical F-actin prior to furrow formation fails to exhibit a normal transition into F-actin-rich arcs, and drug inhibition is consistent with aura function promoting F-actin polymerization and/or stabilization. In mutants, components of exocytic and endocytic vesicles, such as Vamp2, Clathrin and Dynamin, are sequestered in unreleased CGs, indicating a need for CG recycling in the normal redistribution of these factors. However, the exocytic targeting factor Rab11 is recruited to the furrow plane normally at the tip of bundling microtubules, suggesting an alternate anchoring mechanism independent of membrane recycling. A positional cloning approach indicates that the mutation in aura is associated with a truncation of Mid1 Interacting Protein 1L (Mid1ip1L), previously identified as an interactor of the X-linked Opitz G/BBB syndrome gene Mid1. A Cas9/CRISPR-induced mutant allele in mid1ip1L fails to complement the originally isolated aura maternal-effect mutation, confirming gene assignment. Mid1ip1L protein localizes to cortical F-actin aggregates, consistent with a direct role in cytoskeletal regulation. Our studies indicate that maternally provided aura/mid1ip1L acts during the reorganization of the cytoskeleton at the egg-to-embryo transition and highlight the importance of cytoskeletal dynamics and membrane recycling during this developmental period.

Aggregation, segregation, and dispersal of homotypic germ plasm RNPs in the early zebrafish embryo

“…We previously showed that vegetal germ plasm RNPs move animally along meridional cortical arcs and associate with animal germ plasm RNPs that have become recruited to the cortex (Theusch et al, ), and that this animally directed movement is actin‐dependent (Welch and Pelegri, ). We find that embryos mutant for the maternal gene aura/mid1ip1l , encoding a regulator of F‐actin dynamics (Eno et al, ; Eno and Pelegri, ) show a similar defect in animally directed vegetal RNP movement. Despite the absence of vegetal germ plasm RNPs, in these embryos animal RNPs can form aggregates similar to those in wild‐type.…”

“…Using this same assay, we also tested embryos mutant for the maternal effect F‐actin regulator aura/mid1ip1lL (Eno et al, ; Eno and Pelegri, ). As previously shown (Eno and Pelegri, ), aura mutant embryos exhibit a reduction in the number of dnd RNP aggregates in furrows (reduced dnd RNP aggregates at furrows: 19/40 aur t9792 /aur t9792 , 13/20 mid1ip1L uw39 /mid1ip1L uw39 , 0/40 wild‐type) (Fig.…”

Igf2bp3 maintains maternal RNA stability and ensures early embryo development in zebrafish

“…Sperm-egg fusion triggers the process of cortical granule cortical granule exocytosis (CGE) depending on the reorganization of F-actin network in which CGs are embedded 19,20 . Since the organization of F-actin was disrupted in the cleavage furrow, the distribution and exocytosis of CGs were quantified by labeling CGs with TRITC-conjugated Maclura pomifera agglutinin (MPA), which could determine the size and density of CG vesicles 4 . At 2 min post fertilization (mpf), the size and density of CGs were similar between the wild type and Migf2bp3 embryos ( Fig.…”

“…aternally inherited mRNAs direct early developmental events in vertebrates, such as egg activation, fertilization, and embryonic cell division, along with the assembly of cortical cytoskeleton [1][2][3][4] . The post-transcriptional regulatory mechanisms that control maternal mRNA stability and degradation are fine-tuning and complex.…”

A calcium‐mediated actin redistribution at egg activation in Drosophila

“…The reorganization of F-actin following exposure to osmotic pressure in zebrafish oocytes mediates the release of the cortical granules (Becker & Hart, 1999;Hart & Collins, 1991). More recent work in zebrafish has shown that the actin-binding factor, Aura, mediates this reorganization of actin and that in a Aura mutant background F-actin does not rearrange, and cortical granule exocytosis is inhibited (Eno, Solanki, & Pelegri, 2016).…”