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First published online March 31, 2007
Journal of Experimental Biology 210, 1406-1412 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.02753

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Pregnancy block by MHC class I peptides is mediated via the production of inositol 1,4,5-trisphosphate in the mouse vomeronasal organ

Roger N. Thompson, Ronald McMillon, Audrey Napier and Kennedy S. Wekesa

Department of Biological Sciences, Alabama State University, Montgomery, Alabama 36101-0271, USA

View larger version (15K): [in this window] [in a new window]   Fig. 1. Pregnancy failure after exposure to whole urine and urine mixed with MHC class I peptides. MHC class I peptides function as individual identification signals in the circumstance of pregnancy block in mice. A significant pregnancy failure rate was observed when female C57BL/6 mice were mated with C57BL/6 male mice and then exposed to BALB/c male urine or the H-2d haplotype peptide in C57BL/6 urine (*P<0.05). Pregnancy block in females exposed to familiar male urine or the H-2b haplotype peptide was not significant. A significant effect was not observed when C57BL/6 female mice were mated with BALB/c male mice and then exposed to familiar urine. Female C57BL/6 mice mated with BALB/c male mice and exposed to BALB/c male urine supplemented with H-2b haplotype peptide or C57BL/6 male urine showed a significant pregnancy failure rate (*P<0.05).

View larger version (10K): [in this window] [in a new window]   Fig. 2. Pregnancy failure caused by MHC peptides only. Prototypical representative ligands for H-2b and H-2d haplotypes induce pregnancy failure when administered without urinary constituents. C57BL/6 female mice mated with C57BL/6 male mice and exposed to the active form of the MHC peptide specific for the H-2d haplotype resulted in a significant pregnancy failure rate. The inactive H-2d peptide failed to block pregnancy. C57BL/6 female mice mated with BALB/c male mice and exposed to the H-2b haplotype peptide also showed a significant pregnancy failure rate. The inactive form of the H-2b peptide failed to block pregnancy. Alt C57BL/6 and Alt. BALB/c refers to the control peptides, which had their characteristic anchoring residues changed to alanines, i.e. AAPDARETA and SAFPEITHA, respectively.

View larger version (20K): [in this window] [in a new window]   Fig. 3. Pregnancy failure after exposure to urine of juvenile or castrated male mice. MHC class I peptides and urine, in the absence of an androgen influence, are able to induce pregnancy failure. C57BL/6 females mated with C57BL/6 male mice and exposed to C57BL/6 castrated male urine supplemented with the H-2b peptide failed to block pregnancy. However, a significant effect was observed when C57BL/6 females mated with C57BL/6 males were exposed to C57BL/6 juvenile urine supplemented with the H-2d peptide. A significant effect was observed when C57BL/6 females mated with C57BL/6 males were exposed to urine from BALB/c castrated males. Exposure of C57BL/6 female mice mated with BALB/c males to urine of castrated or juvenile C57BL/6 males resulted in a significant pregnancy failure rate, whereas, exposure to urine of BALB/c castrated males failed to block pregnancy. A significant pregnancy failure rate was observed when C57BL/6 female mice were mated with BALB/c males and exposed to urine of C57BL/6 castrated males supplemented with the H-2d peptide. A significant result was again observed when urine from BALB/c castrated males supplemented with the H-2b peptide was applied to the C57BL/6 females mated with the BALB/c males.

View larger version (6K): [in this window] [in a new window]   Fig. 4. Production of Ins(1,4,5)P3 by MHC class I peptides. MHC class I peptides have the ability to stimulate the production of Ins(1,4,5)P3 in vomeronasal organ (VNO) microvillar preparations from female C57BL/6 mice. Reactions were performed without stimulus (PBS only), with whole urine, or active and inactive forms of the H-2b and H-2d haplotype peptides. Synthetic BALB/c peptide (H-2d) stimulates the production of Ins(1,4,5)P3 in the VNO (*P<0.05). The synthetic C57 peptide (H-2b) does not significantly increase Ins(1,4,5)P3 production, and the alternative forms of both peptides result in Ins(1,4,5)P3 levels approximately equal to basal levels, indicating their inability to stimulate Ins(1,4,5)P3 production in the VNO. Values are means ± s.e.m. of at least five independent experiments, each consisting of duplicate measurements.

View larger version (6K): [in this window] [in a new window]   Fig. 5. Production of Ins(1,4,5)P3 after exposure to urine from castrated males. C57BL/6 female vomeronasal organ (VNO) microvillar membranes responded to whole urine and urine from BALB/c castrated males with an increase in the production of Ins(1,4,5)P3 (*P<0.05). The addition of H-2d peptide further increased the production of Ins(1,4,5)P3, though not significantly. Reactions were performed without stimulus, in the presence of whole urine, urine from castrated males, and urine from castrated males supplemented with MHC peptide. Values are means ± s.e.m. of at least five independent experiments, each consisting of duplicate measurements.