Systems genetics approach reveals candidate genes for parasite resistance from quantitative trait loci studies in agricultural species

A systems genetics approach combining pathway analysis of quantitative trait loci (QTL) and gene expression information has provided strong evidence for common pathways associated with genetic resistance to internal parasites. Gene data, collected from published QTL regions in sheep, cattle, mice, rats and humans, and microarray data from sheep, were converted to human Entrez Gene IDs and compared to the KEGG pathway database. Selection of pathways from QTL data was based on a selection index that ensured that the selected pathways were in all species and the majority of the projects overall and within species. Pathways with either up- and down-regulated genes, primarily up-regulated genes or primarily down-regulated genes, were selected from gene expression data. After comparing the data sets independently, the pathways from each data set were compared and the common set of pathways and genes was identified. Comparisons within data sets identified 21 pathways from QTL data and 66 pathways from gene expression data. Both selected sets were enriched with pathways involved in immune functions, disease and cell responses to signals. The analysis identified 14 pathways that were common between QTL and gene expression data, and four directly associated with IFNγ or MHCII, with 31 common genes, including three MHCII genes. In conclusion, a systems genetics approach combining data from multiple QTL and gene expression projects led to the discovery of common pathways associated with genetic resistance to internal parasites. This systems genetics approach may prove significant for the discovery of candidate genes for many other multifactorial, economically important traits.

Embryotoxicity of regressing corpora lutea in ewes

Experiments were performed to test the null hypotheses that embryonic survival is not affected by the presence of regressing corpora lutea in progestogen-supplemented ewes, and that the embryotoxic effects of regressing corpora lutea do not act locally on embryos in the uterine horn adjacent to the regressing corpora lutea. In Expt 1, laparotomies were performed on day 4 after mating, and progestogen supplementation was initiated and continued until pregnancy was diagnosed by ultrasonography on day 25. On day 4 after mating, ewes were lutectomized (n = 17) or sham lutectomized (n = 15), and injected (i.m.) with 5 mg PGF2alpha at 8 h intervals for 2 or 3 days. Controls (n = 14) were sham lutectomized and injected with saline as described above. Pregnancy rates did not differ in ewes treated with PGF2alpha for 2 rather than 3 days. Pregnancy rates were lower in ewes treated with PGF 2a compared with controls (P < 0.01). In ewes treated with PGF2alpha, lutectomy resulted in an increase in pregnancy rates (59%) compared with ewes subjected to sham lutectomy (33%; P < 0.05). In Expt 2, progestogen supplementation was initiated in the morning of day 4 after mating and continued until pregnancy diagnosis on day 25. In the afternoon of day 4, one ovary selected at random was lutectomized in ewes (n = 34) with at least one corpus luteum on each ovary, and the uterine horns were isolated by ligation to impede intraluminal transfer of luteal or uterine products that might initiate embryonic death. On days 5-8 after mating, equal numbers of ewes were injected i.m. with either saline or 5 mg PGF2alpha at 8 h intervals. Pregnancy rates did not differ between isolated uterine horns contralateral and ipsilateral to the regressing corpus luteum; however, pregnancy rates were lower in PGF2alpha-treated ewes than in saline-treated ewes (34 and 77%; P < 0.05). In conclusion, regressing corpora lutea exert an embryotoxic effect; however, there is no evidence that this effect occurs through systemic pathways.

Embryotoxicity of regressing corpora lutea in ewes

Experiments were performed to test the null hypotheses that embryonic survival is not affected by the presence of regressing corpora lutea in progestogen-supplemented ewes, and that the embryotoxic effects of regressing corpora lutea do not act locally on embryos in the uterine horn adjacent to the regressing corpora lutea. In Expt 1, laparotomies were performed on day 4 after mating, and progestogen supplementation was initiated and continued until pregnancy was diagnosed by ultrasonography on day 25. On day 4 after mating, ewes were lutectomized (n = 17) or sham lutectomized (n = 15), and injected (i.m.) with 5 mg PGF2alpha at 8 h intervals for 2 or 3 days. Controls (n = 14) were sham lutectomized and injected with saline as described above. Pregnancy rates did not differ in ewes treated with PGF2alpha for 2 rather than 3 days. Pregnancy rates were lower in ewes treated with PGF 2a compared with controls (P < 0.01). In ewes treated with PGF2alpha, lutectomy resulted in an increase in pregnancy rates (59%) compared with ewes subjected to sham lutectomy (33%; P < 0.05). In Expt 2, progestogen supplementation was initiated in the morning of day 4 after mating and continued until pregnancy diagnosis on day 25. In the afternoon of day 4, one ovary selected at random was lutectomized in ewes (n = 34) with at least one corpus luteum on each ovary, and the uterine horns were isolated by ligation to impede intraluminal transfer of luteal or uterine products that might initiate embryonic death. On days 5-8 after mating, equal numbers of ewes were injected i.m. with either saline or 5 mg PGF2alpha at 8 h intervals. Pregnancy rates did not differ between isolated uterine horns contralateral and ipsilateral to the regressing corpus luteum; however, pregnancy rates were lower in PGF2alpha-treated ewes than in saline-treated ewes (34 and 77%; P < 0.05). In conclusion, regressing corpora lutea exert an embryotoxic effect; however, there is no evidence that this effect occurs through systemic pathways.

Embryotoxic effects adjacent and opposite to the early regressing bovine corpus luteum

Early luteal regression in cattle has an embryotoxic effect that is not overcome by replacement with progesterone, but is prevented by removal of the regressing CL. Two experiments were designed to test the null hypothesis that the luteal component of the embryotoxic effect is delivered by a systemic pathway. Beef heifers and cows (n = 39) received two good quality embryos, one placed into each uterine horn on Day 6 or 7 of the estrous cycle. Treated animals (n = 20) received 15 mg of PGF2alpha three times per day from Day 7 (n = 11; Experiment 1) or 5 (n = 9; Experiment 2) through 8; controls (n = 19) received saline. Progestogen replacement therapy (12 mg flurogestone acetate daily, s.c.) was provided from Day 6 (Experiment 1) or 4 (Experiment 2) until ultrasonographic diagnosis of embryo survival on Day 35 after estrus. The effects of treatment, location of the embryo and location by treatment interaction on embryo survival were tested by Chi square. In Experiment 1, there was no significant difference in embryo survival rate between PGF2alpha-treated and control recipients. In Experiment 2, only 6 of 18 embryos survived to Day 35 when transferred to animals treated with PGF2alpha compared to 12 of 18 in control animals (P< 0.05). The survival of embryos did not differ with location (adjacent or opposite to the regressing CL) or location by treatment interaction. Thus no evidence was obtained to support a local effect of the regressing CL. The embryo mortality associated with luteolytic doses of PGF2alpha in cows receiving replacement therapy with progestogen probably involves compounds that either act systemically or are transported via the uterine lumen to the uterine horn contralateral to the regressing CL.

Increased expression of insulin-like growth factor binding protein-1 during induced regression of bovine corpora lutea

Three experiments were conducted to examine gene expression during induced luteal regression in the cow; the initial purpose was the identification of potential embryotoxins. In experiment 1, changes in gene expression in the corpus luteum (CL) were identified by differential display reverse transcription-polymerase chain reaction (DD-PCR) during the first 72 h of luteal regression in cows treated with prostaglandin F(2alpha) (PGF(2alpha)) on Days 4-7 after estrus. Expression of insulin-like growth factor-binding protein-1 (IGFBP-1) was up-regulated, with greatest expression at 24 h (P < 0.05) after treatment with PGF(2alpha) began. In experiment. 2, IGFBP-1 and its mRNA were quantified in CL collected 24 or 48 h after treatment with PGF(2alpha) on Day 4 or 10 after estrus. Because local mechanisms for exchange of hormones between the ovary and uterus are known in ruminants, uterine flushings were assayed for IGFBP-1 to seek evidence of local transfer of luteal IGFBP-1 to the uterus. IGFBP-1 mRNA was increased (P < 0.05) in CL 24 h after treatment when PGF(2alpha) that began on Day 10, and by 48 h after treatment that began on Day 4. Concentrations of IGFBP-1 increased (P < 0.05) in a pattern similar to mRNA, by 24 h on Day 10, and by 48 h on Day 4. Concentrations of IGFBP-1 in uterine flushings did not change on either day. Concentrations of progesterone decreased (P < 0.05) by 8 h after treatment with PGF(2alpha) that began on Day 10, but not until 24 h after treatment that began on Day 4. In experiment 3, cows received either saline or PGF(2alpha) and CL were collected 2 or 10 h after a single treatment, or 2 h after a second treatment that was given 8 h after the first. Expression of IGFBP-1 was increased by 2 h after treatment with PGF(2alpha) on both Days 4 and 10 after estrus. In conclusion, secretion of IGFBP-1 is increased during luteolysis, and may inhibit the steroidogenic effects of insulin-like growth factor-I (IGF-I), but no evidence was found to implicate IGFBP-1 in the embryotoxic effect of regressing CL.

Fertility and ovum fertilization rate after laparoscopic or transcervical intrauterine artificial insemination of oxytocin-treated ewes

Based on our previous work, we found that exogenous oxytocin induces uterine tetany and cervical dilation, and permits transcervical access to the uterus. However, the oxytocin does not reduce sustained sperm transport from the uterus to the oviducts. Thus, we hypothesized that exogenous oxytocin may be a useful adjunct to transcervical intrauterine AI procedures for sheep: two experiments were conducted to test our hypothesis. In Experiment 1, purebred ewes (n = 75/group) were artificially inseminated intrauterine with either laparoscopic or oxytocin-transcervical (i.e., 200 USP units of oxytocin 30 min before AI) procedures. At 54 h after progestogenated pessaries were removed, ewes were inseminated with 200 x 10(6) sperm/0.25 ml of fresh, extended semen, which was collected from a purebred ram of the corresponding breed. Pregnancy rate was greater (P < 0.05) after laparoscopic (37.5%) than after transcervical AI (0%). Because of the disappointing results of Experiment 1, Experiment 2 was conducted to determine whether oxytocin or the AI procedure per se reduced ovum fertilization rate. Treatments were designed in a 2 x 2 factorial arrangement. At 60 h after norgestomet implant removal and 10 min before either laparoscopic or transcervical (cervical in a saline group) AI with 100 x 10(6) sperm/0.25 ml, ewes (n = 10/group) received an intravenous injection of either isotonic saline or 200 USP units of oxytocin. Fertilization rate, which was determined 72 h after AI, was greater (P < 0.05) after laparoscopic than after transcervical/cervical AI (92.5 vs 28%), but oxytocin treatment did not affect fertilization rate. The results indicate that exogenous oxytocin did not reduce ovum fertilization rate, but the transcervical AI procedure per se seemed to reduce fertilization rate.

Does exogenous progestogen alter the relationships among PGF2 alpha, 13,14-dihydro-15-keto-PGF2 alpha, progesterone, and estrogens in ovarian-intact ewes around the time of luteolysis?

The exact mechanisms controlling uterine secretion of PGF2 alpha are not known. An animal model in which progestogen concentrations are kept high and corpora lutea are allowed to regress should be useful for studying the effects of progestogen and estrogens on uterine secretion of PGF2 alpha. Thus, the primary objectives of this study with ovarian-intact ewes were to determine 1) the effect of 6 alpha-methyl-17 alpha-hydroxyprogesterone acetate (MPA) on luteal life span and changes in jugular and vena caval concentrations of PGF2 alpha, 13,14-dihydro-15-keto-PGF2 alpha (PGFM), progesterone, and estrogens around the time of luteolysis, and 2) the relationships among changes in those compounds. The results indicate that MPA 1) reduced (P < .05) vena caval and jugular PGF2 alpha and PGFM concentrations, 2) did not affect luteal life span or progesterone concentrations, 3) increased (P < .05) jugular concentrations of estrogens, and 4) prolonged (P < .05) the interestrous interval by 7 d. Stepwise regression procedures indicated that MPA disrupted a number of the relationships among PGF2 alpha, PGFM, progesterone, and estrogens in vena caval and jugular plasma. Ovarian-intact, MPA-treated ewes may be useful for determining the mechanisms involved in controlling uterine secretion of PGF2 alpha.

Arachidonic acid metabolism during early development of ovine embryos: a possible relationship to shedding of the zona pellucida

Two experiments were conducted to determine if early ovine embryos produce prostaglandins and if prostaglandins may have a role in the shedding of the zona pellucida, i.e., embryo hatching. For Experiment 1, embryos were collected on day (d) 4, 8, 10, 12 or 14 of pregnancy and incubated with 1 microCi of [14C] arachidonic acid (AA) for 24 h. Based upon high-performance liquid chromatography, embryos from all days converted AA to a number of compounds; the amounts produced differed with day. Primarily, embryos produced an unidentified polar compound, 6-keto-PGF1 alpha, PGF2 alpha, PGE2, 13,14-dihydro-15-keto-PGF2 alpha and PGB2. For Experiment 2, embryos collected on d 7 of pregnancy were incubated for a maximum of 6 d in 500 microL of medium containing either ethanol (control; 20 microL), indomethacin (INDO; 10(-4) M), PGE2 (2 ng) or INDO (10(-4) M) + PGE2 (2 ng). Embryos were evaluated daily for hatching from the zona pellucida. The hatching rates (percentage) for control, INDO, PGE2 and INDO + PGE2 were 46.4, 34.5, 60.0, and 30.0, respectively. There was a main effect (P < .09) of treatment, and the hatching rate for embryos treated with PGE2 alone was greater (P < .05) than that for embryos in any group with INDO. The results indicate that early ovine embryos can convert AA to various compounds in vitro, and prostaglandins may have a role in the hatching of sheep embryos from the zona pellucida.

Exogenous oxytocin dilates the cervix in ewes

Cervical anatomy in ewes usually prevents nonsurgical, intrauterine AI and transcervical embryo transfer (ET), which limits their commercial use in sheep. This study was conducted to determine whether oxytocin would dilate the cervix in ewes and permit passage of a stainless steel rod into the uterus. In Exp. 1, at 44 and 52 h after removal of progestogenated pessaries, ewes were injected i.v. with 0 (saline), 200, 400, or 600 USP units of oxytocin. Immediately before and after treatments, stainless steel rods were used to evaluate cervical dilation and determine whether the uterus could be entered. A rod could not be passed through the cervix and into the uterus in any of the saline-treated ewes. All doses of oxytocin given at 44 and 52 h after pessary removal dilated the cervix and permitted easy passage of a rod into the uterus. At both 44 and 52 h, a stainless steel rod was passed into the uterus in 33 of 43 (77%) of the oxytocin-treated ewes. In 93% (40/43) of these ewes, a rod could be passed into the uterus during either the 44-h or during the 52-h attempt. In Exp. 2, on d 9 after pessary removal, ewes were injected i.v. with oxytocin (400 USP units) at 6 or 12 h after i.v. estradiol-17 beta (0, 100, or 200 micrograms). Cervical dilation was evaluated as in Exp. 1. Dose of estradiol x time of oxytocin affected (P less than .01) the proportion of ewes in which a rod could be passed transcervically into the uterus.(ABSTRACT TRUNCATED AT 250 WORDS)