Taylor D. Laughlin, Jeremy R. Miles, Elane C. Wright-Johnson, Lea A. Rempel, Clay A. Lents and Angela K. Pannier
Although deficiencies in porcine blastocyst elongation play a significant role in early embryonic mortality and establishment of within-litter developmental variation, the exact mechanisms of elongation are poorly understood. Secreted phosphoprotein 1 (SPP1) is increased within the uterine milieu during early porcine pregnancy and contains an Arg-Gly-Asp (RGD) peptide sequence that binds to cell surface integrins on the uterine endometrium and trophectoderm, promoting cell adhesion and migration. The aim of the present study was to evaluate the development of preimplantation porcine blastocysts encapsulated and cultured within alginate hydrogels either supplemented with SPP1 or conjugated with RGD. Blastocysts encapsulated within alginate hydrogels supplemented with SPP1 or conjugated with RGD had increased survival compared with non-encapsulated control blastocysts. In addition, the percentage of blastocysts encapsulated within RGD hydrogels that underwent morphological changes was greater than that of blastocysts encapsulated within standard alginate hydrogels or SPP1-supplemented hydrogels. Finally, only blastocysts encapsulated within RGD hydrogels had both increased expression of steroidogenic and immune responsiveness transcripts and increased 17β-oestradiol production, consistent with blastocysts undergoing elongation in vivo. These results illustrate the importance of the integrin-binding RGD peptide sequence for stimulating the initiation of blastocyst elongation.