title: Exocyst complex protein expression in the human placenta.
abstract: BACKGROUND
  Protein production and secretion are essential to syncytiotrophoblast function and are associated with cytotrophoblast cell fusion and differentiation. Syncytiotrophoblast hormone secretion is a crucial determinant of maternal-fetal health, and can be misregulated in pathological pregnancies. Although, polarized secretion is a key component of placental function, the mechanisms underlying this process are poorly understood.
  
  
  OBJECTIVE
  While the octameric exocyst complex is classically regarded as a master regulator of secretion in various mammalian systems, its expression in the placenta remained unexplored. We hypothesized that the syncytiotrophoblast would express all exocyst complex components and effector proteins requisite for vesicle-mediated secretion more abundantly than cytotrophoblasts in tissue specimens.
  
  
  METHODS
  A two-tiered immunobiological approach was utilized to characterize exocyst and ancillary proteins in normal, term human placentas. Exocyst protein expression and localization was documented in tissue homogenates via immunoblotting and immunofluorescence labeling of placental sections.
  
  
  RESULTS
  The eight exocyst proteins, EXOC1, 2, 3, 4, 5, 6, 7, and 8, were found in the human placenta. In addition, RAB11, an important exocyst complex modulator, was also expressed. Exocyst and Rab protein expression appeared to be regulated during trophoblast differentiation, as the syncytiotrophoblast expressed these proteins with little, if any, expression in cytotrophoblast cells. Additionally, exocyst proteins were localized at or near the syncytiotrophoblast apical membrane, the major site of placental secretion.
  
  
  CONCLUSIONS
  Our findings highlight exocyst protein expression as novel indicators of trophoblast differentiation. The exocyst's regulated localization within the syncytiotrophoblast in conjunction with its well known functions suggests a possible role in placental polarized secretion.
authors.affiliation: Department of Physiology and Cell Biology, Ohio State University, Columbus, OH, USA. Electronic address: gonzalez.394@osu.edu.
authors.forename: I M
authors.initials: IM
authors.lastname: Gonzalez
authors.affiliation: Department of Obstetrics and Gynecology, Ohio State University, Columbus, OH, USA. Electronic address: ackerman.72@osu.edu.
authors.forename: W E
authors.initials: WE
authors.lastname: Ackerman
authors.affiliation: Department of Biomedical Sciences, Western Michigan University School of Medicine, Kalamazoo, MI, USA. Electronic address: Dale.Vandre@med.wmich.edu.
authors.forename: D D
authors.initials: DD
authors.lastname: Vandre
authors.affiliation: Department of Physiology and Cell Biology, Ohio State University, Columbus, OH, USA. Electronic address: robinson.21@osu.edu.
authors.forename: J M
authors.initials: JM
authors.lastname: Robinson
mesh_terms: D002454:Cell Differentiation; D005089:Exocytosis; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D018613:Microscopy, Confocal; D008954:Models, Biological; D010920:Placenta / Q000166:cytology / Q000378:metabolism*; D011247:Pregnancy; D014327:Trophoblasts / Q000166:cytology / Q000378:metabolism; D033921:Vesicular Transport Proteins / Q000378:metabolism*; D020691:rab GTP-Binding Proteins / Q000378:metabolism; D000099193:rab11 GTP-Binding Proteins
chemical_list: D033921:Vesicular Transport Proteins; D020691:rab GTP-Binding Proteins; D000099193:rab11 GTP-Binding Proteins
keywords: Exocyst complex; Placenta; Polarization; RAB11; Trophoblast