title: hnRNP I is required to generate the Ca2+ signal that causes egg activation in zebrafish.
abstract: Egg activation is an important cellular event required to prevent polyspermy and initiate development of the zygote. Egg activation in all animals examined is elicited by a rise in free Ca(2+) in the egg cytosol at fertilization. This Ca(2+) rise is crucial for all subsequent egg activation steps, such as cortical granule exocytosis, which modifies the vitelline membrane to prevent polyspermy. The cytosolic Ca(2+) rise is primarily initiated by inositol 1,4,5-trisphosphate (IP(3))-mediated Ca(2+) release from the endoplasmic reticulum. The genes involved in regulating the IP(3)-mediated Ca(2+) release during egg activation remain largely unknown. Here we report on a zebrafish maternal-effect mutant, brom bones, which is defective in the cytosolic Ca(2+) rise and subsequent egg activation events, including cortical granule exocytosis and cytoplasmic segregation. We show that the egg activation defects in brom bones can be rescued by providing Ca(2+) or the Ca(2+)-release messenger IP(3), suggesting that brom bones is a regulator of IP(3)-mediated Ca(2+) release at fertilization. Interestingly, brom bones mutant embryos also display defects in dorsoventral axis formation accompanied by a disorganized cortical microtubule network, which is known to be crucial for dorsal axis formation. We provide evidence that the impaired microtubule organization is associated with non-exocytosed cortical granules from the earlier egg activation defect. Positional cloning of the brom bones gene reveals that a premature stop codon in the gene encoding hnRNP I (referred to here as hnrnp I) underlies the abnormalities. Our studies therefore reveal an important new role of hnrnp I in regulating the fundamental process of IP(3)-mediated Ca(2+) release at egg activation.
authors: Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, 421 Curie Boulevard, Philadelphia, PA 19104, USA.
authors: Wenyan
authors: W
authors: Mei
authors: Karen W
authors: KW
authors: Lee
authors: Florence L
authors: FL
authors: Marlow
authors: Andrew L
authors: AL
authors: Miller
authors: Mary C
authors: MC
authors: Mullins
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005260:Female; D034441:Heterogeneous-Nuclear Ribonucleoproteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D008870:Microtubules / Q000378:metabolism; D008969:Molecular Sequence Data; D009865:Oocytes / Q000166:cytology / Q000502:physiology*; D010641:Phenotype; D016415:Sequence Alignment; D015027:Zebrafish / Q000196:embryology / Q000502:physiology; D029961:Zebrafish Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D034441:Heterogeneous-Nuclear Ribonucleoproteins; D029961:Zebrafish Proteins; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium