Rat embryonic stem cell

1. An isolated rat embryonic stem cell characterized by having the following properties (a)-(j):

(a) expressing Oct3/4 gene and Nanog gene,

(b) positive for alkaline phosphatase activity,

(c) having an embryoid body forming ability,

(d) expressing SSEA (Stage-Specific Embryonic Antigen)-1 and SSEA-4,

(e) having the same number of chromosomes as does a normal rat cell,

(f) capable of being subcultured and holding the undifferentiated state,

(g) having in vitro pluripotency,

(h) having a potential to differentiate for cells of three embryonic germ lineages,

(i) having teratoma formation ability,

(j) having an ability to produce a chimeric rat.

2. A rat embryonic stem cell obtained by performing a process consisting essentially of the following steps (A)-(E) using a culture medium with 2% or less serum concentration:

(A) culturing a rat blastocyst on inactivated mouse embryonic fibroblasts in a leukemia inhibitory factor (LIF)-free culture medium to form an inner cell mass in the blastocyst,

(B) dissociating the inner cell mass, wherein the dissociated inner cell mass is in a cell aggregate state,

(C) culturing primary embryonic stem cells resulting from a culture of the dissociated inner cell mass on inactivated mouse embryonic fibroblasts until the primary embryonic stem cells can be passaged,

(D) dissociating the primary embryonic stem cells, which can be passaged, wherein the dissociated primary embryonic stem cells are in a cell aggregate state, and

(E) culturing the dissociated primary embryonic stem cells on inactivated mouse embryonic fibroblasts to establish an embryonic stem cell,

wherein a rat leukemia inhibitory factor (rLIF)-containing culture medium is used in steps (C)-(E).

3. The embryonic stem cell of claim 2 , wherein the culture medium comprises a serum replacement reagent.

4. The embryonic stem cell of claim 3 , wherein step (B) comprises a step for mechanically dissociating the inner cell mass.

5. The embryonic stem cell of claim 4 , wherein step (D) comprises a step for mechanically dissociating the embryonic stem cells.

6. A culture kit comprising, as components, a serum replacement reagent, rLIF, and the rat embryonic stem cell of claim 1 .

7. The embryonic stem cell of claim 2 , wherein step (B) comprises a step for mechanically dissociating the inner cell mass.

8. The embryonic stem cell of claim 7 , wherein step (D) comprises a step for mechanically dissociating the embryonic stem cells.

9. The embryonic stem cell of claim 2 , wherein step (D) comprises a step for mechanically dissociating the embryonic stem cells.

10. The embryonic stem cell of claim 3 , wherein step (D) comprises a step for mechanically dissociating the embryonic stem cells.

11. A culture kit comprising, as components, a serum replacement reagent, rLIF, and the rat embryonic stem cell of claim 2 .

12. A culture kit comprising, as components, a serum replacement reagent, rLIF, and the rat embryonic stem cell of claim 3 .

13. A culture kit comprising, as components, a serum replacement reagent, rLIF, and the rat embryonic stem cell of claim 4 .

14. A culture kit comprising, as components, a serum replacement reagent, rLIF, and the rat embryonic stem cell of claim 5 .

15. A culture kit comprising, as components, a serum replacement reagent, rLIF, and the rat embryonic stem cell of claim 7 .

16. A culture kit comprising, as components, a serum replacement reagent, rLIF, and the rat embryonic stem cell of claim 8 .

17. A culture kit comprising, as components, a serum replacement reagent, rLIF, and the rat embryonic stem cell of claim 9 .

18. A culture kit comprising, as components, a serum replacement reagent, rLIF, and the rat embryonic stem cell of claim 10 .