Complexin I is required for mammalian sperm acrosomal exocytosis

Longmei Zhao, Heather R. Burkin, Xudong Shi, Lingjun Li, Kerstin Reim, David J. Miller

Research output: Contribution to journalArticlepeer-review


Regulated exocytosis in many cells is controlled by the SNARE complex, whose core includes three proteins that promote membrane fusion. Complexins I and II are highly related cytosolic proteins that bind tightly to the assembled SNARE complex and regulate neuronal exocytosis. Like somatic cells, sperm undergo regulated exocytosis; however, sperm release a single large vesicle, the acrosome, whose release has different characteristics than neuronal exocytosis. Acrosomal release is triggered upon sperm adhesion to the mammalian egg extracellular matrix (zona pellucida) to allow penetration of the egg coat. Membrane fusion occurs at multiple points within the acrosome but how fusion is activated and the formation and progression of fusion points is synchronized is unclear. We show that complexins I and II are found in acrosome-intact mature sperm, bind to SNARE complex proteins, and are not detected in sperm after acrosomal exocytosis (acrosome reaction). Although complexin-I-deficient sperm acrosome-react in response to calcium ionophore, they do not acrosome-react in response to egg zona pellucida proteins and have reduced fertilizing ability, in vitro. Complexin II is present in the complexin-I-deficient sperm and its expression is increased in complexin-I-deficient testes. Therefore, complexin I functions in exocytosis in two related but morphologically distinct secretory processes. Sperm are unusual because they express both complexins I and II but have a unique and specific requirement for complexin I.

Original languageEnglish (US)
Pages (from-to)236-244
Number of pages9
JournalDevelopmental Biology
Issue number2
StatePublished - Sep 15 2007


  • Acrosome reaction
  • Calcium
  • Egg
  • Extracellular matrix
  • Fertilization
  • Membrane fusion
  • Oocyte
  • Secretion
  • Zona pellucida

ASJC Scopus subject areas

  • Molecular Biology
  • Developmental Biology
  • Cell Biology


Dive into the research topics of 'Complexin I is required for mammalian sperm acrosomal exocytosis'. Together they form a unique fingerprint.

Cite this