hnRNP I is required to generate the Ca2+ signal that causes egg activation in zebrafish

Wenyan Mei, Karen W. Lee, Florence L. Marlow, Andrew L. Miller, Mary C. Mullins

Research output: Contribution to journalArticlepeer-review


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 Ca2+ in the egg cytosol at fertilization. This Ca2+ rise is crucial for all subsequent egg activation steps, such as cortical granule exocytosis, which modifies the vitelline membrane to prevent polyspermy. The cytosolic Ca2+ rise is primarily initiated by inositol 1,4,5-trisphosphate (IP3)-mediated Ca2+ release from the endoplasmic reticulum. The genes involved in regulating the IP3-mediated Ca2+ release during egg activation remain largely unknown. Here we report on a zebrafish maternal-effect mutant, brom bones, which is defective in the cytosolic Ca2+ 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 Ca2+ or the Ca2+-release messenger IP3, suggesting that brom bones is a regulator of IP3-mediated Ca2+ 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 IP3-mediated Ca2+ release at egg activation.

Original languageEnglish (US)
Pages (from-to)3007-3017
Number of pages11
Issue number17
StatePublished - Sep 1 2009
Externally publishedYes


  • Brom bones
  • Ca
  • Cortical granule exocytosis
  • Egg activation
  • IP3
  • Maternal effect
  • Zebrafish
  • hnRNP I

ASJC Scopus subject areas

  • Molecular Biology
  • Developmental Biology


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