Abstract Study question The aim of this study was to examine the relation between the presence of filopodia and the embryo viability in human in vitro fertilised embryos. Summary answer The presence of filopodia related to a faster blastocyst development, a better blastocyst quality and higher morphokinetic scores which indicates a higher embryo viability. What is known already Filopodia are involved in numerous cellular processes, for example cell migration, neuronal extension growth and during embryonic development. There is no uniform name to describe these cytoplasmic string structures in the literature. Beside the frequent presence in different cell functions, we have limited information about its function in human embryos. In the early 2000s, the occurrence of filopodia or cytoplasmic strings at the blastocyst stage was classified as a negative sign of embryo viability, but more recently, it has been described as a positive feature, however, the importance and clinical significance of this structure is still controversial. Study design, size, duration Evaluation of the morphokinetic data on the development of 208 embryos from 78 IVF cycles. Examination was carried out at the Division of Assisted Reproduction, Department of Obstetrics and Gynaecology, Semmelweis University, Budapest between December 2020 and March 2021. Participants/materials, setting, methods Embryos from both conventional IVF (cIVF) and intracytoplasmic sperm injection (ICSI) treatments were analysed and evaluated. The dynamics of embryo development, embryo morphology and morphokinetic scores generated by time-lapse system was compared between the embryos with filopodia (FP+) and embryos without filopodia- (FP-) groups. Main results and the role of chance 81.2% of the embryos had filopodia in blastocyst stage. Embryos created by cIVF had 77%, while embryos fertilised by ICSI had 86% of filopodia presence (p = 0.08). FP+ embryos developed in a greater number into a higher quality blastocyst (52.1% vs 20.5%, p = 0,02), their KIDScore was higher (6.1 ± 2.1 vs 4,7 ± 2,07, p < 0.001) and they showed a tendency of higher implantation rate (39.7% vs 14.3% p = 0.16) than the FP- group. The dynamic of the early embryo development was similar between the two groups, however, FP+ embryos reached blastocyst stage significantly earlier (tB: 103.9 hours vs. tB: 107.6 hours; p = 0.007). Based on our results, there was a higher number of embryos with filopodia than without, and the presence of it is not related to the fertilisation method. These embryos developed faster into a blastocyst stage, their morphokinetic parameters were better. KIDScore and iDAScore embryo evaluation systems also recommend in a greater number the FP+ blastocysts for ET. We could also observe vesicle like transport along the filopodia, which leads us to believe that there might be a molecular communication between the differentiating cell populations. Limitations, reasons for caution Due to the low number of cases, the higher implantation rate is not significant. Wider implications of the findings The examination of this feature improves our knowledge of the early embryonic development and may help us to make decisions about the embryos with higher implantation potential. Trial registration number Not applicable

The objective of this study was to evaluate the effect of different culture systems on the development of human preimplantation embryos. Interim analysis of a prospective study with no true randomization to support decision making regarding which culture systems to use in IVF setting. A total of 137 zygotes from 25 women with at least two embryos fertilized by IVF or ICSI were included in the study. Before fertilization check, zygotes from each patient were allocated to either to sequential (n=71) (Vitrolife G5, Vitrolife) or single (n=66) (Global™, LifeGlobal) culture media. Global™ medium was replenished at day 3. Embryo biopsy was carried out for 17 patients at day 3, and the number of chromosomes was determined by CGH microarray (24Sure, Bluenome). Embryo scores (ES) at day 3 and day 5, as well as blastulation and aneuploidy rates were recorded. Data comparison was carried out using paired t-test and Chi-square analysis. There was a significant difference in ES on day 3 (4.01±0.065 versus 5.30±0.086, p < 0.01) but not at day 5 (3.24±0.120 versus 4.10±0.118, p > 0.05) between the Vitrolife and Global culture systems respectively. The blastulation rate was likewise not different between groups (37.83±1.754 versus 51.59±1.727, p < 0.05). A total of 68 embryos were evaluated for chromosome content. No difference was observed in the frequency of euploid embryos (33.33% (11/33) versus 40% (14/35), p = 0.57) culturing in Vitrolife and Global™ media, respectively. In our setting, higher ES was seen at day 3 using single culture system, but no difference was observed beyond this point in embryo quality and development. Also, the frequency of euploid embryos between culture systems did not differ. At this early point in our comparison, no detrimental effect could be observed using a single culture system. Continuation of the study to include a larger number of embryos along with the evaluation of pregnancy and implantation rates in an extended study is warranted.

Study question: Can inappropriate expression of Boris gene (Brother of the Regulator of Imprinted Sites) lead to embryonic or postnatal developmental abnormalities such as human vascular malformations?Summary answer: We observed that essentially all Boris/rtTA transgenic mice die on the first day of life (P0) and that some of the offspring displayed severe vascular abnormalities and hemorrhages in the brain and eye.What is known already: BORIS is originally found only in spermatocytes within normal tissues and aberrantly expressed in many tumors.Thus, it is defined within the cancer-testis group of genes.More recently, it has been detected in human oocytes, ovary, embryonic stem cells and skin samples.Although the biological data have suggested roles for BORIS in epigenetic reprogramming in testis and in the proliferation of cancercells,littleisknownaboutthemechanismselicitingthesefunctions.Study design, size, duration: Tetracycline inducible triple transgenic mice expressing Boris, testis specific-Cre and a floxed rtTA were generated.Females bred to such males and who were on doxycycline during the pregnancy were followed, and embryonic defects in the offspring were analyzed (n ¼ 10).BORIS expression was also evaluated in human cavernous malformations (n ¼ 6).Participants/materials, setting, methods: The Tet-On tetracycline-inducible Boris gene expression system in mice was studied.Breeding experiments, PCR and quantitative RT-PCR protocols were carried out for further characterization of the transgenes.The histopathological analysis of the human and mouse tissues, immunohistochemistry and Western Blot procedures for Boris were also performed.Main results and the role of chance: We previously described that doxycycline induced transgene expression of Boris throughout embryogenesis results in widespread defects in organogenesis including eye malformations, reduced body size, Abstracts i291 Downloaded from https: