Eight syntaxins, which fall into 5 families based on sequence relatedness, have been identified in rats and, according to
Zhang et al. (1995) , are numbered 1A, 1B , 2A, 2B, 2C, 3A, 4A, and 5A. Syntaxin 4A
encodes a predicted 297-amino acid protein that is 89% identical to the
amino acid sequence of the rat STX4a. Syntaxins are
polypeptides essential for exocytosis.
General function
Comment
Cellular localization
Cytoplasmic
Comment
Ovarian function
Unknown
Comment
Expression regulated by
Comment
Ovarian localization
Oocyte
Comment
This gene was found in a rat ovarian cDNA library (Unigene).Iwahashi K et al reported the expression of the exocytotic protein syntaxin in mouse oocytes.
Syntaxin is an integral membrane protein that is involved in membrane fusion. The exocytosis of the contents of cortical granules, secretory vesicles located in the cortex of an egg, modify the extracellular environment to block additional spermatozoa from penetrating the newly fertilized egg. The aim of this study was to characterize syntaxin expression in mouse oocytes, and to determine the specific isoform that is expressed. Syntaxin was demonstrated in the mouse ovary and in mouse oocytes by both western blot and reverse transcription-polymerase chain reaction analyses. Syntaxin 4 was specifically expressed in metaphase II oocytes. Syntaxin was also immunolocalized within metaphase II oocytes and one-cell embryos with pronuclei using laser scanning confocal microscopy. In metaphase II oocytes, syntaxin was located on the plasma membrane and in the cortex, where cortical granules are present, but was not seen at sites free of cortical granules. In one-cell embryos, no cytoplasmic region was free of syntaxin immunoreactivity. Immunoelectron microscopy detected syntaxin on both the plasma membrane and the vesicle membranes in mouse metaphase II oocytes. In conclusion the results indicate that syntaxin 4 co-localizes with cortical granules and participates in membrane fusion and exocytosis during the cortical reaction.