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Biology and molecular signatures of elongating preimplantation conceptuses in dairy cows
The objectives were to investigate changes in transcriptome of preimplantation conceptuses during the process of elongation and associated changes in the concentration of interferon-tau (IFN-τ) in utero. Lactating dairy cows (n = 160) had estrous cycles synchronized and were subjected to induced ovulation and timed artificial insemination (AI). The day of AI was considered study d 0. On d 15, uteri were flushed and IFN-τ concentration in fluid measured. Recovered conceptuses were classified based on morphology/length as ovoid (OV; 1-4 mm), tubular (TUB; 5-19 mm) and filamentous (FIL; 20-85 mm). A subsample of conceptuses from each group had mRNA extracted and subjected to transcriptome analysis using Affymetrix Gene Chip® Bovine Array (8 OV, 17 TUB, and 17 FIL). The experimental design was considered a prospective cohort study with 3 independent groups. Continuous variables were analyzed by ANOVA using the GLIMMIX procedure of SAS and fitting adequate data distribution. Microarray data were analyzed using Bioconductor software in R environment. Data were preprocessed using Gene Chip Robust Multi-Array function. Limma package was used to fit a linear model and adjust variances by empirical Bayes adjustment. Moderate t-test was performed for all pairwise comparisons and P values were adjusted for multiple testing using the Benjamini and Hochberg false discovery rate. Adjusted P < 0.05 and fold change > 1.5 characterized significant differences. Functional analyses were performed using Ingenuity Pathway Analysis. Concentration of IFN-τ in uterine flushing differed (P < 0.05) among all 3 groups and was lower for cows with OV conceptus, followed by those with TUB and then FIL conceptuses (13.7, 326.8, and 2544.7 ng/mL, respectively). Transcriptome analyses revealed the upregulation of 321 and downregulation of 345 transcripts in the transition from OV to TUB, and the upregulation of 249 and downregulation of 154 transcripts in the transition from TUB to FIL. A total of 1,441 transcripts were differently expressed when OV and FIL conceptuses were compared. Differently expressed genes were associated significantly with cellular movement, cell-to-cell signaling and interaction, cellular assembly and organization, lipid metabolism, small molecule biochemistry, and molecular transport. In conclusion, differences in conceptus morphology/length were associated with distinct concentrations of IFN-τ in utero and remarkable changes in transcriptome of trophectoderm cells that elucidate important cellular events occurring during conceptus elongation.
Keywords: conceptus elongation, transcriptome, dairy cow.