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.

A fundamental biological phenomenon during embryogenesis in animal cells is the process of cell division, an event that divides daughter cells in two. The completion of cytokinesis often results in the asymmetric segregation of cell determinants, thereby allowing the two daughter cells to proceed towards diverse cell fates. Many of these processes are driven and regulated by maternal products already present in the unfertilized egg. A recessive maternal‐effect mutation, aura, was identified in a zebrafish gynogenesis‐based screen. Preliminary evidence indicates that aura affects several events during early development that may be dependent on microtubule cytoskeletal rearrangements. aura mutants exhibit defects in cortical granule exocytosis, the recruitment of cell adhesion components to the furrow, germ plasm segregation and late cytokinesis. A positional cloning approach was used to determine the location and identity of aura. A lesion in a candidate gene has been found and rescue efforts are now underway to confirm the identity of the gene. Cell biology, genetic, and experimental approaches are being used to characterize aura gene function further. Together, these studies will contribute to understanding the function and regulation of aura and its role in the cytokinesis pathway.Sources of funding: NIH Ruth L. Kirschstein NRSA MARC Fellowhship and NIH R01 Grant.