Lack of transplacental transmission of Bartonella bovis

Transplacental transmission of Bartonella spp. has been reported for rodents, but not for cats and has never been investigated in cattle. The objective of this study was to assess vertical transmission of Bartonella in cattle. Fifty-six cow-calf pairs were tested before (cows) and after (calves) caesarean section for Bartonella bacteremia and/or serology, and the cotyledons were checked for gross lesions and presence of the bacteria. None of the 29 (52%) bacteremic cows gave birth to bacteremic calves, and all calves were seronegative at birth. Neither placentitis nor vasculitis were observed in all collected cotyledons. Bartonella bovis was not detected in placental cotyledons. Therefore, transplacental transmission of B. bovis and multiplication of the bacteria in the placenta do not seem likely. The lack of transplacental transmission may be associated with the particular structure of the placenta in ruminants or to a poor affinity/agressiveness of B. bovis for this tissue.

Expression of nuclear and membrane progesterone receptors in the canine oviduct during the periovulatory period

Important reproductive events take place in the canine oviduct in the presence of increasing concentrations of progesterone (P4). To investigate the potential effects of P4 on the canine oviduct, the expression of nuclear (PR) and membrane (PGRMC1 and 2, mPRα, β and γ) P4 receptors was studied by quantitative RT-PCR and immunohistochemistry. Oviducts were collected from Beagle bitches after the onset of pro-oestrus and before the LH peak (Pre-LH), after the LH peak and before ovulation (Pre-ov) and on Days 1, 4 and 7 post-ovulation (n=6 bitches/stage). PR mRNA concentrations decreased from Pre-LH to Day 7 in the ampulla and isthmus, whereas both PGRMC1 and 2 mRNA levels increased over the same period. The main change in mPR expression was an increase in mPRβ and γ mRNAs at Day 7 in the isthmus. Furthermore, PR proteins were expressed in the nuclei of luminal epithelial, stromal and muscular cells, whereas the expression of PGRMCs and mPRs was primarily cytoplasmic and localised in the luminal epithelium. The immunostaining for PR decreased at Day 4 in the stroma and muscle, whereas it remained strong in the epithelium from Pre-LH to Day 7. PGRMC1 staining was strong at Days 4 and 7 whereas PGRMC2 was highly expressed from Pre-ov to Day 7. The most intense immunostaining signals for all three mPRs were observed at Day 7. Our results strongly support the hypothesis that P4 is an important regulator of oviductal functions in the bitch through complementary classical and non-classical P4 pathways.

121 EXPRESSION OF STEROID RECEPTORS IN THE CUMULUS - OOCYTE COMPLEX AROUND OVULATION IN THE BITCH

In the bitch, oocytes are ovulated at an immature stage (prophase I) and resume meiosis in the oviduct, 3 to 4 days after ovulation while they are still surrounded by 2 to 3 layers of cumulus cells. Canine cumulus-oocyte complexes (COC) are exposed to high and changing plasma concentrations of 17β-oestradiol (E2) and progesterone (P4) during the periovulatory period. In order to explore whether oocyte maturation may be regulated by steroids in this species, the expression of E2 (ERα, ERβ) and P4 (nuclear: PR; membrane: PGRMC1, PGRMC2, mPRα, mPRβ, mPRγ) receptors was studied in COC at precise times around ovulation. Ovaries were collected from Beagle bitches during anestrus (n = 4), after the beginning of proestrus, and before the LH peak (Pre-LH, n = 7), after the LH peak and before ovulation (Pre-ov, n = 8), and at Day 1 (n = 11) and Day 4 (n = 8) post-ovulation. Anoestrus COC were recovered from follicles smaller than 1 mm in diameter. The COC at the Pre-LH and Pre-ov stages were aspirated from preovulatory follicles (4.5–6 mm in diameter). Such follicular COC were partially denuded to leave the 2 to 3 innermost cumulus layers firmly attached to the zona pellucida. Post-ovulatory COC, naturally surrounded by 2 to 3 cumulus layers, were recovered by oviductal flushing. Total RNA was extracted from 3 batches of 10 COC per stage, then reverse transcribed. The expression of steroid receptors was assessed in duplicate by qPCR (LightCycler® 480, Roche Diagnostics) using the relative standard curve method and normalized by the geometric mean value of the two most stable reference genes (BGLR and RPS5; NormFinder software) chosen among four genes previously tested. Relative amounts of mRNA levels were compared between stages by ANOVA followed, when necessary, by a Tukey test. The ERα and ERβ expression did not vary significantly with the stage. In contrast, a significant variation between stages in nuclear and 4 membrane P4 receptor expression was observed (P < 0.0001 for PR; P < 0.001 for PGRMC1 and mPRβ; P < 0.05 for PGRMC2 and mPRγ). The PR mRNA levels were significantly higher at Pre-ov than at any other stage. PGRMC1 expression was significantly higher at Pre-ov and Day 4 compared with anestrus and Pre-LH, and was at an intermediate level at Day 1. The expression of PGRMC2, mPRβ, and mPRγ remained low from anestrus to Day 1 and increased significantly at Day 4. Lastly, mRNA levels of mPRα were below the detection limit at all stages. This is the first report of steroid receptor expression in canine COC at precise times around ovulation. The stage-specific variation in expression of nuclear and of several membrane P4 receptors around ovulation suggests a role for P4 in canine oocyte maturation. The exact localisation of these receptors in cumulus cells, oocytes, or both remains to be determined.

183 CANINE EMBRYOS OBTAINED BY INTRACYTOPLASMIC SPERM INJECTION

In vitro fertilization encounters 2 specific difficulties in the canine species, with no puppies born to date: low penetration rates (10–50%) and high polyspermia (around 50% of fertilized oocytes; Saint-Dizier et al. 2001 J. Reprod. Fert. Suppl. 57, 147–150). The objectives of the study were to test whether intracytoplasmic sperm injection (ICSI), which overcomes these 2 obstacles, could allow production of canine embryos, using in vivo- or in vitro-matured oocytes. The time of ovulation was determined on 8 Beagle bitches from our experimental kennel by blood progesterone assay and transabdominal ultrasound examination. After ovariohysterectomy 82 to 100 h after ovulation, 58 metaphase II (MII) oocytes were collected by tubal flushing. In parallel, 88 oocytes from 6 anoestrus bitches were matured in vitro (M199 + 20% fetal calf serum for 72 h in 5% CO2 at 38°C). Sperm was collected from 1 Beagle dog with excellent fertility record at natural mating. The sperm was diluted 1 : 100 in PBS/BSA without any selection process. Intracytoplasmic sperm injection was performed at 38°C in M199 HEPES + 20% BSA (4-μm injection pipette; 120-μm holding pipette). One motile spermatozoon of normal morphology was injected per oocyte. Injected oocytes were cultured in vitro for 48 h after injection (M199 + 20% fetal calf serum in 5% CO2 at 38°C) in 4-well open dishes. Oocytes were then fixed and DNA and tubulin were stained for observation by confocal microscopy (Chebrout et al. 2012 Microsc. Microanal. 18, 483–492). Among the 58 MII oocytes recovered in vivo, 7.4% lysed at injection and 20% degenerated during the 48 h after injection. Among the 40 injected oocytes still alive, 6 fragmented (15%) and 4 developed as embryos [10%; 2-pronuclei (n = 2), 2-cell and 6-cell). None of the other oocytes showed decondensed female chromatin. Among the 88 oocytes incubated for in vitro maturation, 13 (14.8%) reached MII. These were successfully injected; 48 h after injection, 3 were embryos at the 2-cell stage and 10 were at the MII stage with a condensed sperm head. Fifty-one non-mature oocytes were injected; 31 were at the germinal vesicle (GV) stage and the stage of others was not determined. Of the GV oocytes, 71% degenerated during culture after injection. The 9 surviving oocytes were still at the GV stage with condensed sperm head 48 h after injection. In conclusion, canine embryos can be obtained through ICSI. Nevertheless, this procedure induced low activation rates. Development at later stages, especially after transfer into a recipient female, is to be evaluated, in particular for in vitro-produced MII oocytes, of lower cytoplasmic competence (Viaris et al. 2008 Reprod. Fert. Dev. 20, 626–639).

90 CHARACTERIZATION OF A PRIMARY CULTURE OF OVIDUCTAL CELLS IN THE BITCH

The oviduct is of particular importance in canine reproduction as it supports oocyte meiosis resumption, sperm capacitation and storage, fertilization and embryo development to the morula/blastocyst stage for 8 to 10 days post-ovulation. A long-time co-culture with oviducal cells could be employed to improve the yield of reproductive biotechnologies in this species, but no characterisation of canine oviduct cells in vitro has been reported to date. The objectives of this study were to (1) evaluate the viability and proportion of epithelial/fibroblast cells in a primary culture of canine oviducal cells collected around ovulation; (2) study the responsiveness of the cultured cells to steroids. Beagle bitches (n = 9) were ovariectomized between Day –1 and Day +1 around ovulation, and their oviducts were sectioned at the ampulla-isthmus junction. Mucosal cells (including stromal and epithelial cells) were collected by squeezing from the ampulla and isthmus sections and cultured separately at a concentration of 5 × 105 cells/well in 500 μL of M199 + 10% FCS at 39°C for 9 days. At Days 3 and 6, 1 × 106 cells were stimulated with 17β-oestradiol (E2, 20 pg mL–1) or progesterone (P4, 20 ng mL–1) for 6 h. At Days 3, 6, and 9 of culture, the viability of the cells was evaluated using the Live/Dead kit (Invitrogen, Carlsbad, CA, USA), and proportions of fibroblast and epithelial ciliated cells were evaluated by immuno-cytochemistry using anti-vimentin and anti-tubulin antibodies, respectively. At Days 0, 3 and 6, the total RNA was extracted from cells and mRNA levels of the oviduct-specific glycoprotein (OVGP, synthesised by nonciliated epithelial cells), E2 (ERα, ERβ) and P4 (PR) receptors were evaluated by RT-qPCR. The effects of the day of culture and of steroid exposure on mRNA levels were analysed by ANOVA followed by a Tukey test. Cell confluence was observed around Day 6 of culture and more than 90% of cells survived during the 9-day culture period. From Day 3 to Day 9, the proportion of vimentin-positive (fibroblast) cells was greater than 68% in both ampulla and isthmus cells. In contrast, the proportion of epithelial ciliated cells was low at Day 3 (9% in ampulla, 12% in isthmus) and null at Days 6 and 9 in both regions. The mRNA levels of OVGP, ER, and PR decreased significantly after 3 days of culture, and then remained stable in both ampulla and isthmus cells (P < 0.001). The steroid exposure had no effect on gene expression, except for ERα mRNA levels at Day 3, which was increased by E2 and reduced by P4 (P < 0.05). In conclusion, the method of collection did not allow us to collect a high proportion of epithelial oviducal cells. However, the relatively stable gene expression of PR and ER during the culture period provides us with a useful tool to study the steroid regulation of canine oviduct mucosal cell functions.

176 IN VITRO MATURATION OF DOG OOCYTES IN CANINE FOLLICULAR FLUID

In the canine species, assisted reproductive technologies, especially in vitro maturation (IVM) and IVF, are still ineffective. The main limiting factor remains the immaturity of the oocytes collected from anestrus ovaries. The ability of an oocyte to reach the MII stage in vitro is linked to the diameter of its follicle and anestrus oocytes, collected from small (<1 mm) follicles, are profoundly immature (De Lesegno et al. 2008). The objective of this study was to improve cytoplasmic quality by mimicking in vivo conditions; that is, to test the effect of pure preovulatory follicular fluid (FF) on survival and IVM rates of anestrus dog oocytes, in order to improve the nuclear and cytoplasmic maturation of these immature oocytes. Follicular fluids samples were collected from 54 Beagle bitches at 2 stages: before the LH peak (n = 23 bitches) and after the LH peak (n = 31 bitches). Only follicular fluid samples from large (>4 mm) follicles were collected and pooled by stage. Control oocytes were matured in 20% FCS/M199 medium. Groups of 5 oocytes were in vitro matured in 30 μL of follicular fluid, in half-area 96-well plates (5% CO2, 38°C). After 72 h of IVM, oocytes were denuded, fixed, and stained for DNA and tubulin before observation by confocal microscopy, and nuclear stages were classified as GV-A to GV-E, MI, and MII (Reynaud et al. 2012). A total of 460 oocytes were collected from 13 anestrus bitches and allocated to either the control medium (n = 155), the Pre-LH FF (n = 145) or the Post-LH FF (n = 160) groups. After 72 h of IVM, the morphology of the cumulus–oocyte complexes (COC) in the post-LH group was different from that of the others: cumulus cells appeared more compact and darker. Analysis of the nuclear stages showed that the degeneration rate was significantly higher (P < 0.05) in the post-LH group (58.7%) than in the pre-LH (40.9%) or in the control group (34.4%). No significant differences (P > 0.05) were observed between the 3 groups in the rate of immature GVA-B oocytes (36.4, 28.5, and 25.3% in the control, Pre-LH, and Post-LH groups, respectively), in the rate of meiotic resumption (GV-C/D/E, MI, MII stages, 44.4, 51.9, and 38.7% in the control, Pre-LH, and Post-LH groups, respectively). Metaphase II rates were not significantly different (12.1, 8.6, and 4.8% in the control, Pre-LH, and Post-LH groups, respectively). In conclusion, canine COC may survive when exposed to IVM in pure follicular fluid, but the degeneration rate was higher in the post-LH group. The presence of follicular fluid did not inhibit meiosis resumption, but did not significantly improve IVM rates. To better mimic in vivo conditions, IVM in a sequence of media, such as IVM in follicular fluid followed by IVM in oviducal fluid remains to be tested.

Effect of blood handling conditions on progesterone assay results obtained by chemiluminescence in the bitch

Assay of blood progesterone (P4) is commonly practiced to determine the time of ovulation, diagnose luteal insufficiency, and predict time of parturition in bitches. Because of practical constraints, most blood samples cannot be assayed on site immediately after collection. The aim of this work was to evaluate the effects of various sampling and storage conditions on concentrations of P4 as determined by chemiluminescence immunoassay. The blood of 5 Beagle bitches was collected from the jugular vein to study the effect of the type of collection tube (silicone, lithium heparin, EDTA), the storage time of unseparated or separated plasma (2 h to 14 d), and the number of freeze-thaw cycles (1-10) on P4. The effect of each factor was tested within one assay session. None of the factors significantly affected P4. Thus, P4 appears to remain relatively stable in canine blood samples exposed to various processing and storage conditions.

Immunolocalization of progesterone receptors in the canine oviduct around ovulation

In the bitch, oocyte maturation, sperm storage, fertilization and early embryo development take place within the oviducts under high and increasing circulating progesterone concentrations. To investigate the potential effects of progesterone on the canine oviduct, nuclear progesterone receptors (PR) were localized. Oviducts were collected by ovariectomy from adult Beagle bitches during anestrus, after the onset of proestrus but prior to the Luteinizing Hormone (LH) peak (Pre-LH), after the LH peak but before ovulation (Pre-ov) and on Days 1, 4 and 7 after ovulation (n = 3 bitches per stage). The cellular distribution of PR was studied by immunohistochemistry (IHC) in the ampulla, isthmus and tubal part of the utero-tubal junction (UTJ). Plasma progesterone and 17β-oestradiol were assayed on the day of surgery. PR were specifically expressed in the nuclei of epithelial, stromal and muscular cells in the ampulla, isthmus and UTJ. The IHC scores did not vary from one oviductal region to another. However, the epithelium displayed higher scores than the stroma at anestrus, Pre-ov, Days 4 and 7, and also higher scores than muscle at Days 4 and 7 (p < 0.05). Immunohistochemistry scores in the stroma and muscle decreased at Days 4 and 7 compared with previous stages (p < 0.05). Furthermore, muscular IHC scores were positively correlated with circulating 17β-oestradiol concentrations and negatively correlated with circulating progesterone concentrations (p < 0.05). In conclusion, PR were identified in the canine oviduct, with differences in expression between tissues and times around ovulation, suggesting that progesterone may regulate tubal functions and reproductive events in this species.

Timing of the intestinal barrier closure in puppies

As puppies are born with very low immunoglobulin concentrations, they rely on passive immune transfer from ingested colostrum to acquire a protective immunity during the first few weeks of life. The purpose of this study was to describe the timing of gut closure in canine neonates. Twenty-two Beagle puppies received 3 ml of standardized canine colostrum at 0, 4, 8, 12, 16 or 24 h after birth using a feeding tube. Blood immunoglobulins G (IgG, M and A) were assayed 0, 4 and 48 h after colostrum ingestion. IgG absorption rate was significantly affected by the time of colostrum administration, and the IgG concentrations in puppies serum 48 h after administration were significantly higher when colostrum was ingested at 0-4 h of age than at 8-12 h or 16-24 h (1.68 ± 0.4, 0.79 ± 0.07 and 0.35 ± 0.08 g/l, respectively; p < 0.001). In the canine species, gut closure seems thus to begin as early as 4-8 h after birth and to be complete at 16-24 h. Consequently, this phenomenon appears to occur earlier in puppies than in most other species.

69 DIFFERENTIAL AND QUANTITATIVE ANALYSIS OF DOG OVIDUCTAL FLUID

The major reproductive peculiarity of the bitch is that ovulation releases prophase I (germinal vesicle, GV, immature) oocytes. Resumption of meiotic maturation, as well as fertilisation and embryonic development to the morula stage occur in the oviduct. Because the dog is a biomedical model for human diseases and also a model for endangered canid species, the development of assisted reproduction techniques would be of great interest. To date, in vitro-produced canine embryos remain exceptional and no puppy has been born. The main limiting factors of in vitro embryo production are the low oocyte maturation rates, the poor oocyte quality and the high polyspermy. A better knowledge of the composition of oviductal fluid during the periovulatory period may help to mimic the in vivo conditions for in vitro oocyte culture and, thereafter, their fertilisation and embryonic development. The objective of this study was to analyse the oviductal fluid by a label-free quantitative proteomic workflow based on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) protein separation, nano-scale liquid chromatography-tandem mass spectrometry (nano-LC-MS/MS) analysis and quantitative method using spectral counting. Ovarian cycles were followed by vaginal smears, ultrasonography and progesterone blood assays. Oviductal fluids were collected from 3 beagle bitches, after ovariectomies performed 3.5 days after ovulation. After dissection, the ampulla and isthmus were separated and flushed with 50 μL of PBS. Oviductal fluids were submitted to 1D SDS-PAGE and all bands were digested with trypsin. Peptide extracts were analysed on an Ettan multidimensional LC (MDLC) system coupled to a linear ion trap quadrupole (LTQ) mass spectrometer. After protein identification using Mascot server and with Swiss-Prot and National Center for Biotechnology Information (NCBI) databases, bioinformatic processing of data and statistic analysis (t-test with P < 0.05) were performed using the spectral counting quantitative module of the Scaffold software. Using this strategy, 427 proteins were qualitatively identified in canine oviductal fluid. Three proteins were specific of the ampulla, 10 specific of the isthmus and 414 were found in both oviductal parts. Among these common proteins, some were differentially expressed, from 1.25 to 9 times higher (HV303_Human, RLA2_Horse, SPRL1_Human, SODC_CANFA, PROF1_Human, ARF4_Bovin and TRXR1_Bovin). The gene ontology analysis displayed biological pathways specific to the biology of reproduction (6 proteins; RUVB1_Human, OVGP1_Pig, STAT3_Human, PLAK_Human, GPX3_Rat and DYL1_Human). These candidate proteins and especially oviduct-specific glycoprotein and glutathione peroxidase, will now be validated by immunodetection methods.

70 EXPRESSION OF NUCLEAR AND MEMBRANE PROGESTERONE RECEPTORS IN THE CANINE OVIDUCT DURING THE PERIOVULATORY PERIOD

In the bitch, the oviduct is the site of oocyte maturation (Day 1 to 3 after ovulation), sperm transport/capacitation, fertilization (Day 3 to 4) and embryo development to the morula/blastocyst stage (Day 4 to 8). Unlike other mammals, these events occur in the presence of high (>6 ng mL–1) and increasing plasma levels of progesterone (P4), but little is known about the regulation of oviductal functions by P4 in the bitch. The objective of this work was to study the mRNA expression of nuclear (PR) and membrane (PGRMC1, PGRMC2, mPRβ and mPRγ) P4 receptors in the canine oviduct during the periovulatory period. Thirty-six Beagle bitches were ovariectomized at 6 stages: anestrus, before the LH peak (pre-LH), after the LH peak (pre-ov) and after ovulation (Day 1, 4 and 7). Three oviductal regions were collected [i.e. ampulla, isthmus and utero-tubal junction (UTJ)]. Total RNA was extracted and then reverse transcribed. The expression of target genes was assessed in duplicate by quantitative PCR (LightCycler® 480; Roche Diagnostics, Meylan, France) using the relative standard curve method and normalized by the geometric mean of 2 reference genes (RPS19 and GAPDH). Relative amounts of mRNA were compared between groups by ANOVA followed, when necessary, by Duncan's test. The expression of nuclear and membrane P4 receptor mRNA varied according to the stage. Expression of PR mRNA was significantly higher at pre-LH, pre-ov and Day 1 stages [means of 1.8, 1.6 and 1.5 arbitrary units (AU), respectively] than at anoestrus, Day 4 and Day 7 (1, 0.4 and 0.5 AU, respectively) in the ampulla. Same patterns of expression were observed for PR in the isthmus and UTJ. Expression of PGRMC1 and PGRMC2 mRNA were at the lowest level during anoestrus (1 AU) and increased significantly from pre-LH to Day 7 in the ampulla (from 2.2 to 8.3 AU and from 1.3 to 5.4 AU for PGRMC1 and PGRMC2, respectively) and in the isthmus (from 0.4 to 2.6 AU and from 0.5 to 1.8 AU for PGRMC1 and PGRMC2, respectively). In the UTJ, mRNA levels for PGRMC1 and PGRMC2 were the highest at Day 4 (3.9 AU) and pre-LH (2.1 AU), respectively, compared to other stages. Expression of mPRβ mRNA did not vary according to the stage in the ampulla and the isthmus, whereas it was significantly lower at Days 4 and 7 (0.6–0.7 AU) compared to other stages (1–1.2 AU) in the UTJ. Expression of mPRγ was significantly higher at Day 7 (5.0 AU) compared to other stages (0.2–1 AU) in the ampulla and was significantly higher at both anoestrus (1 AU) and Day 7 (0.9 AU) compared to other stages (0.02–0.09 AU) in the isthmus, whereas it did not vary significantly in the UTJ. In conclusion, our data suggests that P4 may be an important regulating factor of oviductal functions and could mediate its actions through genomic as well as non-genomic pathways.

68 TRANSCRIPTIONAL GENOME ACTIVATION IN CANINE EMBRYOS COLLECTED IN VIVO

Early embryonic stages are supported by maternal transcripts from the oocyte cytoplasm. Progressive transcription of embryonic genome is a key step for further embryonic development, especially during in vitro culture. To date, in vitro culture from fertilization to the blastocyst stage is inefficient in the canine species. The objective of this work was to identify minor and major activation in in vivo-produced dog embryos. Ovariectomies were performed in 31 Beagle bitches from 102 to 266 h after ovulation (post-ov), precisely timed by transabdominal ultrasonography. Embryos were collected by tubal flushing with M199-Hepes and immediately transferred into transcription buffer. Transcriptional activity was evaluated through 5-bromouridine 5′-triphosphate (BrUTP) incorporation in nascent RNA, without microinjection (Aoki et al. 1997). Oocytes from anoestrus ovaries were used as positive controls. 5-Bromouridine 5′-triphosphate incorporation was revealed by immunocytochemistry (anti-bromodeoxyuridine primary antibody) and embryonic DNA was stained by ethidium homodimer-2. Staining was quantified under laser scanning confocal microscopy. Transcriptional activity was calculated as (mean nuclear intensity – cytoplasmic mean intensity) × nuclear area and expressed in arbitrary units (AU). It was compared to 1 (similar intensity in nucleus and cytoplasm; i.e. no transcriptional activity) by t-test; levels of transcriptional activity were compared between stages by variance analysis. Seventy embryos (from 7 to 21 per stage) from 31 bitches were analysed, from 2 pronuclei to morula stage. Between 28 and 125 nuclei were quantified per stage. At each stage, transcriptional activity was calculated per embryo and per nucleus. A significant transcriptional activity was detected as early as the 2 pronuclei stage (102–132 h post-ov; 1.15 ± 0.05 AU). Transcriptional activity per embryo significantly increased between the 2- and the 4-cell stage and between the 8-cell and the morula stage. In early 8-cell embryos, staining intensity of the various nuclei was markedly heterogeneous within the same embryo, all nuclei being intensively stained from the late 8-cell stage onwards. Transcriptional activity per nucleus increased also from the 2- to the 4-cell stage (respectively, 120–161 h post-ov, 1.15 ± 0.02 AU and 133–154 h post-ov, 1.35 ± 0.04 AU) until the 8-cell stage (153–225 h post-ov, 5.12 ± 0.55 AU). Transcriptional levels at these 3 stages differed significantly. It decreased between the 8-cell and the morula stage (230–266 h post-ov, 3.06 ± 0.13 AU), probably reflecting the acquisition of a selectivity in gene expression at major activation, as in other species; Nothias et al. 1995). Addition of the transcriptional inhibitor α-amanitin during BrUTP incubation decreased the transcriptional activity by 60% (P < 0.05). Embryonic gene expression (minor activation) thus begins in the canine embryo as early as the 2 pronuclei stage, with major activation taking place during the 8-cell stage.

130 EXPRESSION OF STEROIDOGENIC ENZYMES IN THE CAT OVARY DURING FOLLICULAR GROWTH

This study was designed to describe the expression of steroidogenic enzymes in the various compartments of the feline ovary, from primordial to preovulatory follicles: P450 side-chain cleavage (P450scc), 17α-hydroxylase (17α-OH), 3β-hydroxysteroid dehydrogenase (3β-HSD). Nine female cats were ovariectomized during behavioural oestrus. After validation of their specificity by Western blot on feline tissue, 3 polyclonal antibodies obtained in the rabbit were used for immunohistochemistry (anti-bovine P450scc; anti-pig 17α-OH; anti-human 3β-HSD). Three successive ovarian cryosections were incubated with antibodies and 2 sections were used as controls (purified immunoglobulin G from a nonimmunized rabbit). Immunostaining was revealed by streptavidin-biotin system (LSAB kit, DAKO S.A., Trappes, France), with aminoethylcarbazole as a chromogen. The staining was evaluated according to its localization, intensity (from 1 to 4) and number of cell layers stained. Histological examination after haematoxylin-eosin-safran staining allowed follicle diameter measurement and evaluation of the atresia. Analysis of variance was used to compare follicles from various size classes. A total of 343 follicles from 140 to 3250 μm in diameter were observed (i.e. all follicles present on the slides), of which 15.2% were atretic. The observations were similar for the 3 enzymes. From the preantral stage onward (diameter >140 μm), more than 85% of the healthy follicles had the theca interna positive for P450scc, 3β-HSD and 17α-OH (respectively, 87.3, 86.0 and 99.0%). Approximately 20 to 25% were also positive in the theca externa. Granulosa were stained in 9.5% (P450scc), 0.8% (3β-HSD) and 1.8% (17α-OH) of the healthy follicles, but always with a low intensity (<2). The follicular size did not affect the proportion of stained follicles, but the staining intensity decreased progressively until 1200 μm and increased thereafter. The number of positive layers decreased continuously until 1500 μm in diameter. Between 90 and 95% of the preovulatory follicles (>2000 μm) were positive in the theca interna; the signal was more intense and the number of stained layers was higher than in smaller follicles. The 3 enzymes were detected in all the atretic follicles, with a similar intensity as in healthy ones; they were also present in the interstitial tissue, but with a higher intensity. The staining pattern in the various ovarian compartments suggests that the major steroidogenic tissues in the cat ovary are the theca interna of healthy follicles and the interstitial tissue. The lack of expression of the 3 key enzymes in the granulosa cells, even in preovulatory follicles, strongly suggests that these cells, shaping the future corpus luteum, are probably unable to produce progesterone.

Folliculogenesis and morphometry of oocyte and follicle growth in the feline ovary

This study was designed to describe, both quantitatively (morphometry) and qualitatively (histological differentiation), follicle and oocyte growth in the feline ovary. The ovaries of 43 cats were collected and processed for histology. The diameters of 832 follicle/oocyte pairs were measured, with and without zona pellucida (ZP), and a special emphasis was placed on the study of early folliculogenesis. Primordial, primary, secondary, pre-antral and early antral follicles were measured at 44.3, 86.2, 126.0, 155.6 and 223.8 microm in diameter respectively. A biphasic pattern of follicle and oocyte growth was observed. Before antrum formation, follicle (x) and oocyte (y) size were positively and linearly correlated (y = 0.500x + 20.01, r(2) = 0.89). Antrum formation occurred when the follicle reached 160-200 microm in diameter (when oocyte was at 102 microm). After antrum formation, a decoupling was observed, a minimal increase in oocyte size contrasting with a significant follicle development (y = 0.001x + 114.39, r(2) = 0.01). The pre-ovulatory follicle diameter was approximately 3500 microm and the maximal oocyte diameter was 115 microm. The ZP, absent in primordial and primary follicles, appeared at the secondary stage and reached almost 6 microm at the pre-ovulatory stage. These results suggest that (i) in feline ovary, follicle and oocyte growth pattern is similar to that observed in other mammals; (ii) the antrum forms in 160-200 microm follicles, which represents 5% of the pre-ovulatory diameter and (iii) the oocyte had achieved more than 90% of its maximal growth at the stage of antrum formation.

In vivo meiotic resumption, fertilization and early embryonic development in the bitch

Early development in canine species follows a very specific pattern. Oocytes are ovulated at the germinal vesicle stage and meiotic resumption occurs in the oviduct. However, because of difficulties in the accurate determination of ovulation time and in the observation of oocyte nuclear stage by light microscopy, these early events have not been fully described. Moreover, the oocyte stage at which sperm penetration occurs is still uncertain since fertilization of immature oocytes has been reported in vivo and in vitro. The aim of this study was to establish the exact timing of in vivo meiotic resumption, fertilization and early embryo development in the bitch with reference to ovulation. Ovulation was first determined by ultrasonography, artificial inseminations were performed daily and oocytes/embryos were collected between 17 and 138 h after ovulation. After fixation and DNA/tubulin staining, the nuclear stage was observed by confocal microscopy. Of the 195 oocytes/embryos collected from 50 bitches, the germinal vesicle stage was the only one present until 44 h post-ovulation, and the first metaphase II stage was observed for the first time at 54 h. Sperm penetration of immature oocytes appeared to be exceptional (three out of 112 immature oocytes). In most cases, fertilization occurred from 90 h post-ovulation in metaphase II oocytes. Embryonic development was observed up to the eight-cell stage. No significant influence of bitch breed and age on ovulation rate, maturation and developmental kinetics was observed. However, some heterogeneity in the maturation/development process was observed within the cohort of oocytes/embryos collected from one bitch. In conclusion, the most peculiar aspect of the canine species remains oocyte meiotic maturation whereas fertilization follows the same pattern as in other mammals.