O presente experimento foi realizado com o objetivo de avaliar o impacto da inseminação artificial em tempo fixo (IATF) na eficiência reprodutiva de vacas de leite de alta produção inseminadas no período pós-parto. Vacas Holandesas com média de 50 dias pós-parto foram distribuídas homogeneamente em um de dois grupos experimentais, levando em consideração a presença ou ausência de corpo lúteo (CL), o escore de condição corporal e a produção de leite. No grupo Controle (G-Controle; n = 490), as vacas foram submetidas à observação do comportamento de aceitação de monta (duas vezes ao dia por uma hora) e inseminadas 12 horas após a primeira detecção. No grupo IATF (G-IATF; n = 495), as vacas receberam um implante auricular de norgestomet, mantido por oito dias, e 2 mg de benzoato de estradiol IM no dia 0 (D0; dia aleatório do ciclo estral). No momento da retirada do implante (D8) foram administrados 150 µg de prostaglandina F2α, 400 UI de gonadotrofina coriônica eqüina e 1 mg de cipionato de estradiol. A IATF foi realizada de 54 a 56 h após a retirada do implante auricular, concomitante à administração de 100 µg de gonadorelina. Após a IATF, as vacas foram submetidas à observação de cio com subseqüente inseminação, seguindo os mesmos critérios descritos para o G-Controle. Amostras de sangue foram colhidas de um subgrupo de animais (G-Controle, n = 50; G-IATF, n = 58) 5 e 11 dias após a primeira inseminação artificial (IA) para dosagem de progesterona (P4) circulante. Todos os animais foram mantidos no experimento até a terceira IA ou 150 dias após o parto e os tratamentos foram realizados no inverno e no verão. O diagnóstico de gestação foi realizado aos 30 dias pós-IA por ultrassonografia e aos 60 dias pós-IA por palpação transretal. Os dados binomiais foram analisados por regressão logística utilizando o PROC GLIMMIX e as variáveis contínuas por ANOVA utilizando PROC GLM do SAS. Não se verificou interação entre estação do ano e tratamento na análise das taxas de concepção, perda gestacional, intervalo entre IAs, intervalo parto-concepção (IPC) e taxa de prenhez aos 150 dias pós-parto. Os resultados são indicativos de que não existem diferenças nas taxas de concepção entre os diferentes grupos após as IAs (primeira, segunda e terceira). A perda gestacional relativa à primeira IA foi maior nas vacas do G-IATF. Os intervalos parto-primeira IA, parto-segunda IA e parto-concepção foram inferiores para as vacas do G-IATF. Entretanto, o intervalo entre a primeira e a segunda IA foi maior para o G-IATF. Não houve diferença na taxa de prenhez aos 150 dias entre os grupos. Ainda, a taxa de serviço (TS) nos primeiros 21 dias após o período voluntário de espera (PVE) foi maior para o grupo IATF. Entretanto, a TS entre 21 e 42 dias após o PVE foi maior para o G-Controle. As concentrações circulantes de P4 não diferiram entre os grupos e as estações do ano. Concluiu-se que o emprego da IATF 60 dias pós-parto foi eficiente para diminuir o IPC. Contudo, a porcentagem de vacas prenhes aos 150 pós-parto foi semelhante entre os dois tratamentos (Controle e IATF) / The aim of the present study was evaluate the impact of fixed-time artificial insemination (FTAI) on reproductive efficiency of high-producing dairy cows inseminated during the postpartum period. Holstein cows with average 50 days in milk were allocated to one of two groups considering the presence or absence of corpus luteum (CL), body condition score and milk production. On Control group (Control-G; n = 490), the cows were submitted to estrus detection twice per day for one h and were inseminated 12 hours after the first detection. On FTAI group (FTAI-G; n = 495), the cows received a norgestomet ear implant (kept for eight days) plus administration of 2 mg of estradiol benzoate i.m. on Day 0 (random day of the estrous cycle). The implant was removed on Day 8 followed by FTAI 54 to 56 h later and the administration of 100 µg of gonadorelin. On Day 8, cows received 400 IU eCG, 150 &micro:g of prostaglandin F2α and 1 mg of estradiol cypionate. After FTAI, cows were submitted to estrus detection and artificial insemination (AI) 12 h after. Blood samples were collected from a subset of animals (Control-G, n = 50; FTAI-G, n = 58) on Day 5 and 11 after the first AI to investigate serum progesterone concentration (P4). All animals were maintained on the experiment until 150 days post-partum and the treatments were conducted during the winter and summer. Pregnancy diagnosis was performed by ultrasonography 30 days after AI (Day 30) and by rectal palpation 60 days after AI (Day 60). Binomial data were analyzed by logistic regression using the PROC GLIMMIX and continuous variables by ANOVA using PROC GLM of SAS. No interaction was found between season and treatment when conception rate, pregnancy loss, interval between inseminations, interval from calving to conception and pregnancy rate 150 post-partum were analysed. The results indicate no differences on conception rate among both experimental groups after AI (first, second and third). However, the interval from calving to first and second AI and interval from calving to conception were lower on FTAI-G. No difference on pregnancy rate 150 days post-partum was found among groups. Pregnancy loss after first AI was greater on FTAI-G. The interval from calving to first AI, from calving to second AI and the interval from calving to conception were shorter on FTAI-G. However, the interval between first and second AI was longer on FTAI-G. There was no difference on pregnancy rate 150 days post-partum among treatments. Also, the service rate (SR) 21 days after the voluntary waiting period (VWP) was greater on FTAI-G compared to Control-G. Conversely, the SR was lower between 21 and 42 days after the VWP on FTAI-G. No difference was found in serum concentration of P4 among treatment groups and season. Thus, the use of FTAI 60 days post-partum was efficient to anticipate the conception of high-producing dairy cattle by reducing the interval from calving to conception, but did not increase the pregnancy rate 150 days post-partum

Biotecnologias como a Ovum Pick-Up e a Produção In vitro de embriões (OPU-PIVE) tem sido uma importante ferramenta para alcançar o melhoramento genético rápido nos rebanhos, diminuindo o intervalo entre gerações. No Brasil, a PIVE está em fase de crescimento e representa 70,7% de toda a produção in vitro mundial. Contudo a OPU-PIVE é ainda ineficiente em vacas de leite, especialmente devido à sua reduzida população folicular. Muitos estudos têm mostrado um efeito positivo do FSH em gado de leite e corte. Recentemente, a pré-estimulação com FSH mostrou ser capaz de aumentar o diâmetro dos folículos aspirados e a porcentagem de embriões transferíveis. O FSH estimula o recrutamento dos folículos na fase antral, fazendo com que eles possam se desenvolver até o momento em que ocorre a divergência e um ou mais folículos se torne dominante. A hipótese do presente estudo é que o uso de FSH (200 mg), fracionado em 4 ou 6 aplicações, em vacas holandesas não lactantes, com emergência de onda folicular sincronizada, aumenta o número de folículos ovarianos, o número de oócitos viáveis e a quantidade de embriões na produção in vitro. Trinta e seis vacas Holandesas não lactantes foram utilizadas como doadoras de oócitos e distribuídas em três tratamentos: Controle (C), 4 aplicações de FSH (F4) e 6 aplicações de FSH (F6). Todas as vacas foram submetidas ao mesmo protocolo de sincronização de emergência de onda folicular, diferindo apenas pela administração e número de 4 ou 6 doses de FSH, conforme descrito acima. Em dia aleatório do ciclo estral (D0), todas as vacas receberam um dispositivo de P4 (Primer®, Tecnopec-Agener União, São Paulo, SP, Brasil) e 2 mg de benzoato de estradiol (Ric-BE®, Tecnopec-Agener União, São Paulo, SP, Brasil). Três dias após (D3), foi administrado 0,530 mg de Cloprostenol Sódico (Cioprostinn®, Innovare Biotecnologia e Saúde Animal Ltda, Monte Aprazível, SP, Brasil), induzindo a luteólise com a intenção de liberar espaço no estroma ovariano para o crescimento folicular e facilitar a visualização de folículos na OPU. Vacas do grupo C não receberam tratamentos adicionais. Vacas do grupo F4 receberam 200 mg de FSH (Folltropin - Bioniche Anim,al Health, Belleville, ON, Canadá) fracionados em 4 aplicações de equivalentes concentrações em intervalos de 12 h, iniciando no D4 pela manhã. Vacas do grupo F6 receberam 200 mg de FSH fracionados em 6 aplicações de equivalentes concentrações em intervalos aproximados de 12 h, tendo início no D3 pela manhã. No D7, o dispositivo foi removido e a OPU realizada concomitantemente à contagem dos folículos existentes nos ovários. Os oócitos considerados viáveis foram fertilizados in vitro com sêmen sexado de touros da raça Holandesa. Os dados foram analisados pelo PROC GLIMIX do SAS 9.3, utilizando contrastes ortogonais C1 (C x FSH) e C2 (F4 x F6). Não houve efeito de tratamento no número de folículos (C = 53,3 ± 4,9 vs FSH = 51,36 ± 3,1;P = 0,89), número total de oócitos (C = 19,46 ± 1,64 vs FSH = 18,47 ± 1,27; P = 0,55), número de oócitos viáveis (C = 12,57 ± 1,26 vs FSH = 12,70 ± 1,03; P= 0,606), taxa de recuperação de oócitos (C = 36,5% vs FSH = 36,0%; P = 0,48) e produção de embriões in vitro (C = 4,11 ± 0,52 vs FSH = 4,32 ± 0,46; P = 0,79). Apesar de não ter havido efeito no número de folículos, o tratamento com FSH alterou a distribuição dos mesmos, proporcionando o aumento no número de folículos médios (6 a 10 mm). No entanto, não houve efeito do tratamento com FSH no número de oócitos totais e viáveis recuperados, nem na produção de embriões. / Reproductive biotechnologies such as Ovum Pick-Up and in vitro Embryo production (OPU-IVEP) have been widely used as important tools to achieve faster genetic improvement in herds, diminishing the intervals between generations. In Brazil, in vitro Embryo Production (IVEP) is growing in popularity and accounts for 70.7% of all in vitro embryo production worldwide. However, the OPU-IVEP is still poorly efficient in high-producing dairy cattle, especially because of their reduced follicular population. Several studies have shown a positive effect of FSH on OPU-IVEP yeld. Recently, FSH pre-stimulation has shown to be able to increase the diameter of aspirated follicles and the percentage of transferable embryos. The hormone FSH stimulates follicle recruitment in the antral phase, in the way that they develop until the moment of divergence and one or more follicles becomes dominant. The hypothesis of this study is that the use of 200mg FSH split into 6 doses in non-lactating Holstein cows with a synchronized follicular wave emergence increases the number of follicles, the recovery rate and the number of embryos produced in vitro. Thirty six Holstein cows used as oocyte donors were homogenously allocated to one of three treatment groups in a 3x3 Latin square design: Control (C); 4 doses of FHS (FSH4); 6 doses of FSH (F6). All cows were synchronized using the same protocol for synchronization of follicular wave emergence, except for the administration and number of doses of FSH as previously described. At random days of the estrous cycle known as D0, all cows received an intravaginal P4 device (Primer®, Tecnopec-Agener União, São Paulo, Brazil) and 2mg estradiol benzoate (Ric-BE®, Tecnopec-Agener União). Three days after (D3), all cows received 0.530 mg D-Cloprostenol (Cioprostinn®, Innovare Biotecnologia e Saúde Animal Ltda, Monte Aprazível, SP, Brasil). Cows from the Control group received no additional treatment. Cows from group FSH4 were treated with 200 mg of FSH split in 4 doses of similar concentration given approximately 12 h apart, starting on D4 AM. Cows form group FSH6 were treated with 200 mg of FSH split in 6 doses of similar concentration given approximately 12 h apart, starting on D3 AM. On D7, the device was removed and OPU was performed concomitant with antral follicle count in each ovary. The oocytes considered as viable were sent to IVEP. Data was analyzed using the Glimmix of SAS 9.3, with orthogonal contrasts C1 (C x Treatment with FSH) and C2 (FSH4 x F6). There was no effect on the number of antral follicle (C = 53.3 ± 4.9 vs FSH = 51.36 ± 3.1;P = 0.89), number of total oocytes (C = 19.46 ± 1.64 vs FSH = 18.47 ± 1.27; P = 0.55), number of viable oocytes (C = 12.57 ± 1.26 vs FSH = 12.70 ± 1.03; P= 0.61), oocyte recovery rate (C = 36.5% vs FSH = 36.0%; P = 0.48) and number of embryos produced in vitro (C = 4.11 ± 0.52 vs FSH = 4.32 ± 0.46; P = 0.79). Although FSH treatment did not affect the number of follicles, it affected the distribution of them, increasing the number of follicles from 6 to 10 mm. However, FSH treatment did not alter the total number of oocytes and number of viable oocytes or embryo production.

A factorially designed experiment had 18 Hereford and 18 Holstein steers on individually fed, high-grain diets. One diet included 59% rolled barley, 30% CSF beet pulp, 5% protein, vitamin, mineral, and stilbestrol supplement, and 6% chopped hay and straw. The other diet had corn silage (11% air dry matter equivalent) substituted for the chopped roughage and 5% of the beet pulp. The Holsteins were heavier at the start, 752 lb. as compared to the Herefords 686 lb. average. The weight differential was maintained throughout the approximately 180-day trial. The Holstein's feed consumption and rate of gain, 23.4 and 2.71 lb. respectively, were significantly better than the hereford's 20.1 and 2.23 lb. The average feed conversion difference was not significant, with 8.68 for the Holsteins and 9.20 for the Herefords. There was no significant difference in carcass grade, although the Herefords tended to grade higher and had significantly better conformation scores. The Holsteins had less fat cover, .178 inches as compared to .497 inches, and a significantly higher cutability, with 52% for the Holsteins vs. 50% for the Herefords. Feed conversion was 8.57 for the cattle on the diet containing silage and 9.30 for those on the diet without silage (P<.05). This experiment's relatively low level of silage apparently improved palatability and minimized the wastage of "fines." The relatively large variations in all measures among individual animals were considered a significant observation.

Three non-lactating Holstein cows fitted with rumen cannula were used to determine crude protein and dry matter rate of disappearance of two protein supplements: 1) soybean meal and 2) bypass protein blend by using the in situ bag technique. Rate disappearance (%/hr) was higher for soybean meal. Two collection periods were completed using 6 cows with a minimum of 21 d adaptation to the treatment top dressed on to the total mixed ration. Ruminal concentration of ammonia N, blood ammonia, and urea did not differ between treatments. Total concentration of volatile fatty acids was higher for bypass protein blend-fed cattle as well as percent molar concentration of propionate, butyrate, and valerate, while pH was lower. Total protozoa, and total and cellulolytic viable bacteria populations did not differ. Four of the cows received a dose of 5 ml of Prostaglandin F,a. Blood and cervical muc us samples obtained showed no difference in blood ammonia and urea concentration . Forty-six Holstein cows were assigned to one of the two treatments (top dressed on the t otal mixed ration), according to parity during the following 125 d postpartum. Daily dry matter intake and milk production were recorded. Feed, orts, and feces were sampled. Milk samples were collected weekly and analyzed for components. Percent lactose and solid non-fat showed higher for cattle fed the bypass prorein blend. Starting on day 10 postpartum, cows were observed for signs of estrus and bred at first estrus observed after 45 d postpartum. Cervical mucus and blood collected at first standing estrus, and first, seco nd, and third service, did not show a significant difference in urea concentration between rations. Twice-weekly collected blood samples showed similar monthly mean concentration of ammonia, urea, and progesterone profile for both treatment groups. Percent pregnancy, services per pregnancy, first service pregnancy and embryo mortality showed no significant difference. Motility and survivability of bull sperm were evaluated by incubating thawed semen in different levels of previously observed and/or ammonia. physiological There were no concentrations of urea significant treatment differences observed. Detrimental effects of treatment on sperm were not detected.

Several studies suggest that the administration of GnRH near the time of insemination improves pregnancy rates in cattle. It has also been reported that there is greater improvement in repeat-breeder animals than at first service. The mechanism for this observation has not been established. Twenty-eight lactating Holstein cows that returned to estrus after one or more inseminations from the usu caine Dairy were used in the study. Anilrals were rarxiomly divide:i into tW'O treatment groups, intrarmJscular administration of 100 ug GnRH or saline oontrol at the tirre of insemination. Blood samples were collected at o, 1, 1.5, 2, 2.5, 3 and 4 hours post-insemination for LH determination and on days 0 through 7, 10, 16 and 22 for progesterone determination. Pregnancy status was detennined by rectal palpation 40 to 47 days post insemination. serum IR concentrations reached peak concentrations (9.33 ± 5.5 ng/ml) by one hour following GnRH administration. This was significantly different from saline controls (p Serum progesterone levels increased as expected. from day o to day 16 in all animals. Animals treated with GnRH that became pregnant tended to have the highest progesterone levels beginning from day 4. Animals treated with GnRH that were non-pregnant at 40 to 47 days tended to have the lowest progesterone levels from days 4 through 10 but were high on day 16. Pregnant animals had higher progesterone levels than non-pregnant animals from days 4 to 16. These differences approached significance (0.25 > p < 0.10). These results support the contention that GnRH administration affects progesterone levels rut do not conclusively establish increased early progesterone levels as the mechanism for improved pregnancy rates. Other hormonal andl functional factors may be involved.

Die postovulatorische Alterung sowie die ovarielle Alterung konnten bei der Anwendung assistierter Reproduktionstechniken (ARTs) als entscheidende Faktoren identifiziert werden, die den Reproduktionserfolg nachhaltig beeinträchtigen. Die postovulatorische Alterung tritt ein, sobald die reife Eizelle nicht mehr innerhalb ihres physiologischen Zeitfensters befruchtet wird. Die ovarielle Alterung beschreibt hingegen die Abnahme des Follikel-Vorrats mit zunehmendem Alter des weiblichen Individuums bzw. des Ovars. Sowohl die postovulatorische Alterung als auch die ovarielle Alterung führen u.a. zu einer reduzierten Oozytenqualität und einer geringeren Blastozystenrate. Die Zielsetzung dieser Arbeit bestand darin, den Einfluss der postovulatorischen Alterung und der ovariellen Alterung im Holstein-Rind (Bos taurus) auf die DNA-Methylierung entwicklungsrelevanter Gene in Eizellen und Embryonen zu untersuchen. Aus Schlachthof-Ovarien wurden Antralfollikeln unterschiedlicher Größe (<2 mm, 3-5 mm und >6 mm) isoliert. Eizellen aus Follikeln der Größe 3-5 mm wurden für 24h (physiologisch) und 48h (gealtert) in vitro gereift (IVM). Die gereiften Oozyten wurden anschließend in vitro fertilisiert und Embryonen im 4-6 Zellstadium generiert. Sowohl in den unreifen Eizellen aus Antralfollikeln unterschiedlicher Größe als auch in den gereiften Oozyten und den Embryonen wurde die Promotormethylierung der Gene bH19, bSNRPN, bZAR1, bDNMT3A, bOCT4, bDNMT3Lo und bDNMT3Ls analysiert. Zur Untersuchung der ovariellen Alterung wurden mittelgroßen Antralfollikel aus Ovarien lebender Rinder (in vivo) unterschiedlichen Alters (9-12 Monate, 3-7 Jahre und 8-11 Jahre) gewonnen. In den daraus isolierten unreifen Eizellen wurde die DNA-Methylierung der Promotorregionen der Gene bTERF2, bREC8, bBCL-XL, bPISD, bBUB1, bDNMT3Lo, bH19 und bSNRPN bestimmt. Als Methode zur Analyse der Promotormethylierung wurde die Limiting Dilution Bisulfit-Sequenzierung angewendet. In unreifen Eizellen aus Antralfollikeln unterschiedlicher Größe (<2 mm, 3-5 mm und >6 mm) konnte ein erhöhtes Auftreten abnormal methylierter Allele in den geprägten Genen bH19 und bSNRPN von Eizellen kleiner Follikel (<2 mm) identifiziert werden. Dieses Ergebnis könnte eine mögliche Ursache einer bereits bekannten und mehrfach beschriebenen geringeren Entwicklungskompetenz von Eizellen kleiner Follikel (<2 mm) auf epigenetischer Ebene darstellen. Die verlängerte Reifungsdauer der IVM-Eizellen hatte eine signifikante Hypermethylierung in der Promotorregion des Gens DNMT3Lo von 48h-gereiften Eizellen zur Folge. Beim Übergang von 48h-gereiften Eizellen zum Embryo konnte eine signifikante Hypomethylierung von CpG7 des stammzellspezifischen Transkripts DNMT3Ls beobachtet werden. Diese CpG-Stelle wies ebenfalls einen signifikanten Anstieg von CpGs mit nicht-eindeutigem Methylierungszustand in unreifen Eizellen mit steigender Follikelgröße auf. Da sich die CpG-Position innerhalb eines Sequenz-Motivs einer Bindungsstelle des Transkriptionsfaktors CREB befindet, könnten die Methylierungsdaten auf eine Interaktion zwischen dem Transkriptionsfaktor CREB und der DNA-Methylierung während der Entwicklung und Reifung der Eizelle sowie der Transition von der Eizelle zum Embryo hindeuten. Die DNA-Methylierungsprofile der untersuchten Gene in unreifen Eizellen aus Kühen unterschiedlichen Alters (9-12 Monate, 3-7 Jahre und 8-11 Jahre) wiesen keine signifikanten Unterschiede zwischen den Altersgruppen auf. Die ovarielle Alterung bei Rindern zwischen 9 Monaten und 11 Jahren zeigte damit keinen Effekt auf die DNA-Methylierung der untersuchten Promotorregionen der Gene bTERF2, bREC8, bBCL-XL, bPISD, bBUB1, bDNMT3Lo, bH19 und bSNRPN. Nach einer simulierten postovulatorischen Alterung durch eine in vitro Reifung für 48h konnte eine Veränderung der DNA-Methylierung der Oozyten-spezifischen (DNMT3Lo) und Stammzell-spezifischen (DNMT3Ls) Promotoren des katalytisch inaktiven Cofaktors von DNMT3A, DNMT3L, beobachtet werden. Die veränderte DNA-Methylierung von DNMT3Ls tritt dabei erst im frühen Embryo in Erscheinung und interagiert vermutlich mit dem Transkriptionsfaktor CREB. Die Veränderungen von DNMT3Lo in Eizellen und DNMT3Ls in den daraus generierten Embryonen lässt vermuten, dass es sich hierbei um eine dynamische Anpassung des Embryos auf äußere Umweltbedingungen der Eizelle über die Methylierung der DNA handelt. / Postovulatory aging and ovarian aging have been identified as key factors in assisted reproductive techniques (ARTs) and have a lasting effect on reproductive success. Postovulatory aging occurs if the mature egg is not fertilized within its physiological time window. On the other hand, ovarian aging describes the decrease in the follicular reserve with increasing age of the female or the ovary, respectively. Both post-ovulatory aging and ovarian aging result in reduced oocyte quality and lower blastocyst rate. The aim of this thesis was to explore the effects of postovulatory aging and ovarian aging in Holstein cattle (Bos taurus) on the DNA methylation of developmentally important genes in oocytes and embryos. Antral follicles of different sizes (<2 mm, 3-5 mm and> 6 mm) were isolated from slaughterhouse ovaries. Female germ cells from middle-sized follicles (3-5 mm) were matured for 24h (physiological conditions) and 48h (aged conditions) in vitro (IVM). The IVM- oocytes were subsequently fertilized in vitro and embryos at the 4-6 cell stage were generated. Promoter methylation of the genes bH19, bSNRPN, bZAR1, bDNMT3A, bOCT4, bDNMT3Lo and bDNMT3Ls was analysed in immature oocytes from antral follicles of different sizes as well as in matured oocytes and the respective embryos. For studying ovarian aging, middle-sized antral follicles were obtained in vivo from animals of different age groups (9-12 months, 3-7 years and 8-11 years). In the extracted immature gametes, the DNA methylation of the promoter regions of bTERF2, bREC8, bBCL-XL, bPISD, bBUB1, bDNMT3Lo, bH19 and bSNRPN was examined. The limiting dilution bisulfite (pyro)sequencing method was applied to determine the promoter methylation of the candidate genes at the single allele level. In immature oocytes from antral follicles of different diameters (<2 mm, 3-5 mm and> 6 mm) an increased occurrence of abnormally methylated alleles of the imprinted genes bH19 and bSNRPN was identified in small follicles (<2 mm). This failure to establish imprinting could be a possible cause of a well-known reduced developmental potential of small follicles (<2 mm) at the epigenetic level. The extended maturation time of the IVM-oocytes resulted in a significant hypermethylation in the promoter region of DNMT3Lo in 48h matured oocytes. After transition from 48h matured oocytes to embryos, a significant hypomethylation of CpG7 of the stem cell specific transcript DNMT3Ls was detected. The same CpG site showed a significant increase of CpGs with unclear methylation state in immature female germ cells with increasing follicular size. This CpG position is located within a potential binding site of the transcription factor CREB. Thus, the methylation data indicates an interaction between the transcription factor CREB and the DNA methylation during development and maturation of oocytes as well as during transition from the oocyte to the embryo. The DNA methylation profiles of the analysed genes in immature oocytes from cows of different age (9-12 months, 3-7 years and 8-11 years) showed no significant differences between age groups. Hence, the ovarian aging in cattle between 9 months and 11 years caused no effect on the DNA methylation of bTERF2, bREC8, bBCL-XL, bPISD, bBUB1, bDNMT3Lo, bH19 and bSNRPN. After a simulated postovulatory aging by in vitro maturation for 48h, a change in the DNA methylation of the oocyte-specific (DNMT3Lo) and stem cell-specific (DNMT3Ls) promoters of the catalytically inactive DNA-methyltransferase DNMT3L was observed. The altered DNA methylation of DNMT3Ls occurs in the early embryo and probably interacts with the transcription factor CREB. The changes of DNMT3Lo in oocytes and DNMT3Ls in the resulting embryos might represent a dynamic adaptation to external environmental conditions.

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Dissertation--Kiel--Christian-Albrechts-Universität, 2003. Titre de soutenance : Demokratisierung und Neubildung einer politischen Elite in Schleswig-Holstein 1945 bis 1950. / Bibliogr. p. 218-237.

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