Persistent baculovirus infection is observed frequently in insect populations. Persistent infection can be transformed to a replicative and infective state caused by stress factors and plays an important role in regulating the size of insect population and in epizoology of baculoviruses. The aim of this study is to establish a persistently baculovirus-infected cell system to explore the molecular mechanisms of baculoviral persistence. Spodoptera exigua nucleopolyhedrovirus (SeMNPV) was serially undiluted passaged in Se301 cells to reduce virulence. Upon infection of Se301 cells with the SeMNPV up to passage 8, a few cells survived even if most of cells died due to virus infection. The surviving cells were passaged and designated as P8-Se301 cell strain. P8-Se301 cells had a population doubling time of 58-65 hours and grew slower than Se301 cells. Light microscopy and electron microscopy observation showed symptom of baculovirus infection, such as virogenic stroma, viral particles and occlusion bodies, in some of P8-Se301 cells. End-point dilution assay and infectious center assay showed that 4.14% +/- 0.99% cells continually released infectious progeny virus which replicated slower than SeMNPV in Se301 cells. The result indicated that P8-Se301 cells show a typical character trait of baculovirus persistent infection.
Animals ; Cells, Cultured ; Nucleopolyhedrovirus ; growth & development ; physiology ; Spodoptera ; virology ; Virus Cultivation ; methods

Objective To analyze the characteristics and variation of occipital protuberance and occipital bunning of Chinese Holocene population. Methods Based on 275 adult male skulls, Neolithic Age ( 49 cases ), Bronze and Iron Age (171 cases) and modern (55 cases), the occipital protuberance and occipital bunning were divided into several categories, and the occurrence rates were analyzed and compared among different time periods. Results The characteristics and variation of occipital protuberance and occipital bunning were also different in different ages. The degree of the occipital protuberance was more and more significant with the age, which changed greatly from Neolithic Age to Bronze and Iron Age. In the Holocene, most people did not appear occipital bunning on the skull, but the relatively significant occipital bunning appeared in the Bronze and Iron Age. Conclusion The variation of occipital protuberance may be related to the change of skull size and overuse of trapezius muscle in Holocene. The occipital bunning appearance may reflect the relative development speed of the brain and skull to some extent.