341 FELINE EMBRYONIC STEM-LIKE CELLS DERIVED FROM IN VITRO-PRODUCED BLASTOCYSTS RETAIN IN VITRO DIFFERENTIATION POTENTIAL

Abstract

Embryonic stem (ES) cells are pluripotent cells that can differentiate into all 3 germ layers, including endoderm, mesoderm, and ectoderm. Embryonic stem cells are generally divided into 2 types, naïve and primed-state, depending on their signaling pathways. Domestic cat is a useful animal model for the study of human diseases because many genetic and infectious diseases in the cat are analogous with similar aetiology to human diseases. The cat can also be used as a research model for reproductive physiology and conservation of wild felids. Until recently, information on establishment of feline ES cells is limited. The objectives of this study were to isolate cat ES cells from in vitro-produced blastocysts and to examine the effect of different concentrations of basic fibroblast growth factor (bFGF) on the expression of pluripotent genes. Inner cell masses (ICM) from cat blastocysts (n = 40, Day 7 after in vitro fertilization) that were matured, fertilized, and cultured entirely in vitro, were isolated by immunosurgery and plated on mitmycin-treated mouse embryonic fibroblasts. The ICM (n = 20) were then cultured in embryonic stem cell medium containing 1000 IU mL^–1 of leukemia inhibitory factor (LIF) and different bFGF concentrations (0, 4, 10, and 20 ng mL^–1). The ICM outgrowths at 7 days postplating were collected and analysed for expression of pluripotent genes (SOX-2, OCT-4, and NANOG). Results showed that transcription levels of all 3 pluripotent genes were higher in ICM outgrowths cultured in 20 ng mL^–1 of bFGF compared with the lower concentrations. For isolation of ES cells, ICM (n = 20) were cultured in embryonic stem cell medium supplemented with 1000 IU mL^–1 of LIF and 20 ng mL^–1 of bFGF due to the results obtained from the above experiment. Established ES cells were characterised by detecting alkaline phosphatase (AP) activity and expression of ES markers (SOX-2, OCT-4, SSEA-4) at protein level, and karyotyped at passage 20 and 40. In vitro differentiation into embryoid bodies (EB) was induced by the hanging drop technique, and EB samples (n = 5 for each time point) were tested for the expression of TTR, AFP, T (Bracyury), NKX2.5, MAP-2, and NESTIN genes at 0, 7, and 14 days of culture. A total of 3 ES-like cell lines were established with a typical ES morphology, such as a well-defined colony, a large nucleus to cytoplasm ratio with 1 to 2 prominent nucleoli. The 3 ES-like cell lines were passaged up to 40 times with a normal diploid karyotype (n = 38). They were strongly positive for AP, SOX-2, OCT-4, and SSEA-4. Following EB culture, cell aggregation and cystic-like structure were observed. The EB samples also expressed all differentiation markers. This study reports that feline ES-like cell lines can be generated from in vitro-produced feline blastocysts. The ES cell lines can be repeatedly passaged indicating self-renewal ability, and gene expression of the EB demonstrates cellular differentiation into all 3 germ layers.