205 DERIVATION OF CAT EMBRYONIC STEM-LIKE CELLS FROM IN VITRO-PRODUCED BLASTOCYSTS AND THEIR SUPPORT BY INTRASPECIFIC VS. INTERSPECIFIC FEEDER CELLS

Abstract

Interspecific nuclear transfer has been successfully demonstrated in nondomestic cats (Gomez et al. 2004 Cloning Stem Cells 6, 247); however, the efficiency remains low and may be attributable to nuclear reprogramming errors. Embryonic stem cells (ESC) may complete nuclear reprogramming more efficiently than somatic cells and, therefore, are potentially useful for increasing cloning success (Jaenisch et al. 2002 Cloning Stem Cells 4, 389). The objectives of this study were to: (1) compare efficiency of immunosurgery vs. mechanical separation for isolating the inner cell mass (ICM) of in vitro-derived cat blastocysts; and (2) determine the influence of mouse (MEF: CF-1) and cat (CEF) embryonic fibroblast feeder layers on ICM attachment and growth of ES-like cells. After ICMs were isolated from in vitro-derived blastocysts (n = 142) by immunosurgery or mechanically, they were plated either on mitotically inactivated CEF (40 ¼L/mL Mitomycin-C; 5 h) or MEF (30 ¼L/mL Mitomycin-C; 2.5 h). Cells were cultured in DMEM-F12, 1 mM L-Glutamine, 0.1 mM 2-mercaptoethanol, 1.25% nonessential amino acids, 15% knock-out replacement serum, 5% fetal bovine serum, 40 ng/mL leukemia inhibitory factor, 5 ng/mL basic fibroblast growth factor, 100 IU penicillin, 100 ¼g/mL streptomycin, and 25 ¼L/mL amphotericin-B in a humidified atmosphere of 5% CO₂ in air at 38°C. Our results indicated that ICM isolation and attachment were not affected by either the method of isolation (immunosurgery: 75.8 ± 6.9% vs. mechanical: 89.5 ± 6.4%) or the feeders (MEF: 74.6 ± 6.7% vs. CEF: 90.7 ± 6.6%). However, the incidence of ES-like cell colony formation was significantly affected by the feeder layer (CEF: 55.4 ± 7.2% vs. MEF: 12.7 ± 7.2%; P < 0.001). A total of 32 ES-like cell lines were derived on CEF (n = 26) and MEF (n = 6), of which 50% were alkaline phosphatase (AP)-positive. One ES-like cell line derived on MEF spontaneously differentiated into myocardiocytes after 14 days in culture. Three ES-like cell lines derived on CEF were immunostained for ESC-markers Oct-4, SSEA-1, and SSEA-4, and for AP. Positive results for all markers were observed in a few colonies of each line, with colonies from one cell line appearing on Day 23 and remaining in culture for 102 days (12 passages). Colonies from the other two cell lines appeared on Day 17 and remained in culture for 78 days (9 passages). Colonies derived on MEF appeared on average at 17.9 days and remained in culture an additional 15 to 61 days without further characterization. The present results describe the first isolation of cat ES-like cells. We have demonstrated an important species-specific relationship between feeder layers and the derivation of cat ESCs. Further studies are in progress to improve culture conditions for the derivation and expansion of stable cat ESC lines.