title: Comparison of cell viability and embryoid body size of two embryonic stem cell lines after different exposure times to bone morphogenetic protein 4.
abstract: BACKGROUND
  Activation of bone morphogenetic protein 4 (BMP4) signaling pathway in embryonic stem (ES) cells plays an important role in controlling cell proliferation, differentiation, and apoptosis. Adverse effects of BMP4 occur in a time dependent manner; however, little is known about the effect of different time exposure of this growth factor on cell number in culture media. In this study, we investigated the role of two different exposure times to BMP4 in cell viability, embryoid body (EB), size, and cavitation of ES cells.
  
  
  METHODS
  Embryonic stem cells (R1 and B1 lines) were released from the feeder cell layers and were cultured using EBs protocol by using the hanging drop method and monolayer culture system. The cells were cultured for 5 days with 100 ng/mL BMP4 from the beginning (++BMP4) or after 48 h (+BMP4) of culture and their cell number were counted by trypan blue staining. The data were analyzed using non-parametric two-tailed Mann-Whitney test. P<0.05 was considered as significant.
  
  
  RESULTS
  In EB culture protocol, cell number significantly decreased in +BMP4 culture condition with greater cavity size compared to the ++BMP4 condition at day 5 (P=0.009). In contrast, in monolayer culture system, there was no significant difference in the cell number between all groups (P=0.91).
  
  
  CONCLUSIONS
  The results suggest that short-term exposure of BMP4 is required to promote cavitation in EBs according to lower cell number in +BMP4 condition. Different cell lines showed different behavior in cavitation formation.
authors.affiliation: Laboratory for Stem Cell Research, Department of Anatomical Sciences, School of Medicine, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: Nehleh
authors.initials: N
authors.lastname: Zarei Fard
authors.affiliation: Laboratory for Stem Cell Research, Department of Anatomical Sciences, School of Medicine, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: Tahereh
authors.initials: T
authors.lastname: Talaei-Khozani
authors.affiliation: Laboratory for Stem Cell Research, Department of Anatomical Sciences, School of Medicine, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: Soghra
authors.initials: S
authors.lastname: Bahmanpour
authors.affiliation: Laboratory for Stem Cell Research, Department of Anatomical Sciences, School of Medicine, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: Tahereh
authors.initials: T
authors.lastname: Esmaeilpour
keywords: Bone morphogenetic protein 4; Embryoid body; Embryonic stem cells
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