57 Primordial germ cell distribution in the horse fetal gonad

Germ cell development and differentiation is a complex process associated with down-regulation of stem cell-associated genes and up-regulation of markers of germ cell differentiation and meiosis. In horses, putative primordial germ cells (PGCs) were identified outside the gonads starting 20 days after ovulation (Curran et al. 1997 Equine Vet. J. Suppl. 25, 72-76). However, no information is available after the time when these cells enter the gonad. The aim of this study was to identify, localise, and quantify PGCs in fetal male and female gonads. Twelve (5 males and 7 females) equine fetuses were collected transcervically 60 days after ovulation. Fetuses were entirely fixed in formaldehyde and gonads were subsequently localised. Fetal gonads underwent multiplex immunofluorescence staining for pre-meiotic germ cell marker LIN28, stem-cell associated marker CD117, and cell proliferation marker Ki67. Specificity of the primary antibodies for equine samples has been first validated. Quantification of fluorescence positive areas for LIN28, CD117, and Ki67 in the fetal gonads was done using a macro for ImageJ. Furthermore, we analysed the co-localization of above-mentioned markers using the same macro. Statistical comparison for differences between males and females was performed using non-parametric tests. In both sexes, PGCs proliferated as determined by double immunofluorescence of Ki67 and LIN28. Protein expression of LIN28 and Ki67 was highly correlated (r=0.92; P=0.003). In the fetal female gonad, PGCs were organised in cord-like structures localised in the cortical region, but there were also LIN28+ cells in the surface germinal epithelium. In the fetal male gonad, PGCs were restricted to the already developed tubular structures. Fewer LIN28+ cells (3.0±0.4% vs. 4.5±0.3%; P<0.05) were present in female than in male gonads. The distribution pattern of the stem cell factor receptor CD117 was similar to LIN28, as 86.8±3.2% of LIN28+ cells in females and 84.6±4.7% in males were also CD117+. However, immunofluorescent co-localization analysis revealed a subpopulation of CD117+ cells (43.1±8.1% in females and 46.1±6.1% in males), which did not show an overlap with LIN28. These were presumably stem cells localised in the medullar area of the gonad. In summary, we analysed for the first time spatial distribution of PGCs in fetal equine gonads. We demonstrated LIN28 to be a specific marker for PGCs also in the horse gonad, which is in agreement with the situation in human and other species. Furthermore, we identified stem cells and described their localization in the fetal equine gonad. Nevertheless, the temporal distribution of PGC and stem cells in the developing horse gonad and the role of LIN28 in the maintenance of the germline stem cell state still need to be investigated.

46 Morphologic and functional characterization of the early fetal equine gonads

In the equine embryo, putative primordial germ cells appear between 20 and 30 days and the gonadal primordium can first be identified at Day 30 after ovulation, respectively. Subsequently, sexual differentiation of the gonad occurs and completes by Day 45 of pregnancy. The objectives of this work were to describe the morphology and function of the fetal equine ovary and testis at the beginning of the fetal stage of pregnancy. For this purpose, 12 equine fetuses (6 males and 6 females) were collected at 45 days (n=1, female), 50 days (n=1, male), and 60 days (n=10, 5 males and 5 females) after ovulation, respectively. A high attention was given to Day 60 because it is the representative time for fetal sex determination in horses by transrectal ultrasonography. Conceptuses were collected transcervically by uterine lavage and fixed in 4% formaldehyde before being prepared for morphology analysis and immunohistochemistry assay. Gonads were identified and immunostained for anti-Müllerian hormone (AMH), Ki67, CD117, LIN28, vimentin, cytokeratin, and laminin. In all fetuses, gonads were situated in a sublumbar localisation and connected with the mesonephros. In females, primordial germ cells were localised close to the surface germinal epithelium, whereas in males the primordial germ cells were organised in cord-like clusters-the future seminiferous tubules. At this stage, interstitial cells predominate in the testes. The AMH staining was strongly expressed in the fetal testis, but was completely absent from the fetal ovary. Protein expression of mitosis marker Ki67 was localised in primordial germ cells of both sexes. Moreover, stem cell markers LIN28 and CD117 were also present in the gonads. In females, these proteins were not only localised in some of the primordial germ cells, but also in the surface germinal epithelium, whereas in males LIN28 and CD117 were immunolocalized in the seminiferous tubules, distant from the surface epithelium. Vimentin was strongly expressed in the interstitial cells of the gonads of both sexes. Using laminin staining, basal membrane of the seminiferous tubules in males and of primordial germ cells in females could be visualised. In females, the basal membrane of primordial germ cells also stained positive for cytokeratin, whereas in males no cytokeratin staining was seen around seminiferous tubules. Moreover, the surface germinal epithelium of both sexes stained positive for cytokeratin. This study widely extends existing knowledge about morphology, development, and function of the early fetal equine gonad. Presence of stem cells could be clearly demonstrated in the gonads of both sexes, whereas AMH staining clearly distinguished between males and females, confirming the important role of this hormone for gonadal and reproductive tract differentiation.

Comparison of cushioned centrifugation and SpermFilter filtration on longevity and morphology of cooled-stored equine semen

This study compares two methods for seminal plasma removal by evaluating sperm recovery rates, and motility and morphology of cooled-stored semen. Ejaculates were divided into three groups: control, filtration and cushioned centrifugation. Semen was extended to 25 million sperm/ml using a skim-milk-based extender and stored at 5°C for all groups. Sperm motility (total motility (%TM) and progressive motility (%PM)) was determined at 0, 24, 48 and 72 hours by a computer-assisted sperm analyser. Sperm morphology was assessed using differential interference microscopy. Overall, %TM of the centrifugation group was significantly higher than the filter group, but not significantly different than the control. No significant difference in %TM or %PM was detected for the control group and filter. Cushioned centrifugation was a superior method to obtain progressively motile sperm compared with control (P=0.03) and filter groups (P<0.001). No significant difference was found for the per cent of normal sperm cells and detached heads between the groups. This study demonstrated that cushioned centrifugation was a superior method to remove seminal plasma while preserving %TM and enhancing %PM for stallions under cooled storage over three days. However, as the differences appear to be negligible, the SpermFilter may represent an alternative for farms lacking a centrifuge.