title: Intercellular transport of Oct4 in mammalian cells: a basic principle to expand a stem cell niche?
abstract: BACKGROUND
  The octamer-binding transcription factor 4 (Oct4) was originally described as a marker of embryonic stem cells. Recently, the role of Oct4 as a key regulator in pluripotency was shown by its ability to reprogram somatic cells in vitro, either alone or in concert with other factors. While artificial induction of pluripotency using transcription factors is possible in mammalian cell culture, it remains unknown whether a potential natural transfer mechanism might be of functional relevance in vivo. The stem cell based regeneration of deer antlers is a unique model for rapid and complete tissue regeneration in mammals and therefore most suitable to study such mechanisms. Here, the transfer of pluripotency factors from resident stem cell niche cells to differentiated cells could recruit more stem cells and start rapid tissue regeneration.
  
  
  RESULTS
  We report on the ability of STRO-1(+) deer antlerogenic mesenchymal stem cells (DaMSCs) to transport Oct4 via direct cell-to-cell connections. Upon cultivation in stem cell expansion medium, we observed nuclear Oct4 expression in nearly all cells. A number of these cells exhibit Oct4 expression not only in the nucleus, but also with perinuclear localisation and within far-ranging intercellular connections. Furthermore, many cells showed intercellular connections containing both F-actin and α-tubulin and through which transport could be observed. To proof that intercellular Oct4-transfer has functional consequences in recipient cells we used a co-culture approach with STRO-1(+) DaMSCs and a murine embryonic fibroblast indicator cell line (Oct4-GFP MEF). In this cell line a reporter gene (GFP) under the control of an Oct4 responsive element is only expressed in the presence of Oct4. GFP expression in Oct4-GFP cells started after 24 hours of co-culture providing evidence of Oct4 transfer from STRO-1(+) DaMSCs to Oct4-GFP MEF target cells.
  
  
  CONCLUSIONS
  Our findings indicate a possible mechanism for the expansion of a resident stem cell niche by induction of pluripotency in surrounding non-niche cells via transfer of transcription factors through intercellular connections. This provides a new approach to explain the rapid annual antler regrowth.
authors.affiliation: Research Group Experimental Osteology, Department of Maxillofacial Surgery, University Medical Center, University of Goettingen, Goettingen, Germany. hrolf@uni-goettingen.de
authors.forename: Hans J
authors.initials: HJ
authors.lastname: Rolf
authors.forename: Sabine
authors.initials: S
authors.lastname: Niebert
authors.forename: Marcus
authors.initials: M
authors.lastname: Niebert
authors.forename: Lena
authors.initials: L
authors.lastname: Gaus
authors.forename: Henning
authors.initials: H
authors.lastname: Schliephake
authors.forename: K Günter
authors.initials: KG
authors.lastname: Wiese
mesh_terms: D000818:Animals; D000999:Antlers / Q000166:cytology; D001692:Biological Transport; D002450:Cell Communication / Q000502:physiology*; D018920:Coculture Techniques; D003670:Deer; D053595:Embryonic Stem Cells / Q000166:cytology / Q000502:physiology; D059630:Mesenchymal Stem Cells / Q000166:cytology / Q000502:physiology; D051379:Mice; D023421:Models, Animal; D050814:Octamer Transcription Factor-3 / Q000378:metabolism* / Q000502:physiology; D039904:Pluripotent Stem Cells / Q000166:cytology / Q000502:physiology; D012038:Regeneration; D055153:Stem Cell Niche; D013234:Stem Cells / Q000166:cytology*
chemical_list: D050814:Octamer Transcription Factor-3; C494174:Pou5f1 protein, mouse