RESUMEN
Despite the pest status and medicinal value of the American cockroach Periplaneta americana, few attempts have been made to establish cell lines from this insect owing to the difficulty of culturing Blattarian cells. Here, we describe the establishment of the RIRI-PA1 line from P. americana embryo tissue following primary culture in modified Grace's medium containing 20% fetal bovine serum. RIRI-PA1 was found to primarily consist of attached spindle-shaped and giant cells, which attach themselves to their container. The population-doubling time of 40th-passage cells was approximately 84.8 h. The average chromosome number at the 30th passage was 42, with 40% of cells demonstrating substantial variations, with the highest number of variations of 78 and lowest of 24. The identity of RIRI-PA1 was confirmed by comparing the COI gene of these cells to that of P. americana embryo tissue. Telomerase activity decreased in primary cells after 7 d of culture and 5th-passage cells in comparison to embryo tissues; however, compared to the other cultured cells tested, the telomerase activity significantly increased at the 20th passage. We propose that the stagnation periods and cessation of proliferation observed relate to cellular telomerase activity, but the relationship between insect cell proliferation and telomerase as well as the regulatory mechanism involved remains to be elucidated.