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The HeLa cell line is the oldest, most widely distributed, permanent human cell line. As a nearly ubiquitous inhabitant of laboratories using tissue culture techniques, its aggressive growth characteristics make it a problematic contaminant that can overgrow less robust cell lines. Consequently, HeLa contamination is common in both the research laboratory and cell line repository contexts, and its detection is hampered by the lack of a rapid, sensitive and robust assay. Here we report the development of a HeLa-specific DNA diagnostic test: a single duplex detection PCR assay targeting an L1 retrotransposon insertion. All HeLa clones from a geographically diverse panel were positive by this assay, and the particular L1 insertion we identified appears to be unique to the HeLa cell line. The assay can detect very low levels of HeLa contamination (<1%), and can be performed on un-purified cell pellets, allowing rapid routine screening.

In the present study, we demonstrate the existence of two distinct apoptotic patterns in nurse cells during Ceratitis capitata oogenesis. One is developmentally regulated and normally occurs during stages 12 and 13, and the other is stage specific and is sporadically observed during stages 7 and 8. The pre-apoptotic manifestation of the first pattern begins at stage 11 and is characterized by the formation of actin bundles. Subsequently, at stages 12 and 13, the nurse cell nuclei exhibit condensed chromatin and contain fragmented DNA, as revealed by TUNEL assay. The apoptotic nurse cell remnants are phagocytosed by the neighboring follicle cells at the end of oogenesis during stages 13 and 14. In the second apoptotic pattern, which occurs sporadically during stages 7 and 8, the nurse cells degenerate and are phagocytosed by the follicular epithelium that contains apoptotic cell bodies. The data presented herein, compared to previous reported results in Drosophila melanogaster and Dacus oleae (Nezis et al., 2000, 2001), strongly suggest that nurse cell apoptosis is a developmentally regulated and phylogenetically conserved mechanism in higher Dipteran. They also suggest that, the sporadic apoptotic pattern consists of a possible protective mechanism throughout oogenesis when damaged or abnormal egg chambers, are eliminated before they reach maturity.