Submitted January 11, 2008
Returned for revision February 11, 2008
Accepted April 7, 2008
Pregnancy
Integrin Activation in Bovine Placentomes and in Caruncular Epithelial Cells Isolated from Pregnant Cows
Philip S. Bridger ,
Susanne Haupt ,
Rudolf Leiser ,
Gregory A. Johnson ,
Robert C. Burghardt ,
Hans-Rudolf Tinneberg ,
and
Christiane Pfarrer *
* To whom correspondence should be addressed. E-mail: christiane.pfarrer{at}tiho-hannover.de.
Abstract
In the bovine synepitheliochorial placenta, restricted trophoblast invasion requires complex interactions of integrin receptors with proteins of the extracellular matrix (ECM) and integrin receptors of neighboring cells. Activated integrins assemble to focal adhesions and are linked to the actin cytoskeleton via signaling molecules including alpha-actinin (ACTN), focal adhesion kinase (PTK2 or FAK), phosphotyrosine and talin (TLN1). Aims of this study were to assess integrin activation and focal adhesion assembly within epithelial cells of bovine placentomes and low passage (not transformed) placentomal caruncular epithelial cells cultured on dishes coated with ECM proteins. Immunofluorescence analysis was performed to co-localize the signaling molecules ACTN, PTK2, phosphotyrosine and TLN1 with each other and with beta1-integrin (ITGB1) in placentomal cryosections throughout pregnancy and in caruncular epithelial cells in vitro. Antibody specificity was confirmed by Western blot. Cells were cultured on uncoated dishes and dishes coated with fibronectin (FN), laminin (LAMA) and collagen IV (COL4) thereby statistically assessing cell number and qualitatively assessing the expression pattern of ITGB1, phosphotyrosine and TLN1. Results demonstrated integrin activation and focal adhesion assembly in the placentome and that low passage caruncular epithelial cells maintain integrin associated properties observed in vivo. Expression and/or co-localization of signaling molecules with ITGB1 confirmed, for the first time, integrin activation and participation in "outside-in" and "inside-out" signaling pathways. The prominent role of ECM, and FN in particular, in integrin signaling is supported by the in vitro enhancement of proliferation and focal adhesion expression. Thus, this in vitro model provides excellent potential for further mechanistic studies designed to elucidate feto-maternal interactions in the bovine placentome.
Key words:
Pregnancy •
bovine placentome •
caruncular epithelium •
extracellular matrix •
integrin activation
