The rodlet cell of Semotilus atromaculatus and Catostomus commersoni (Teleostei): studies on its identity using histochemistry and DNase I – gold, RNase A – gold, and S1 nuclease – gold labeling techniques

Rodlet cells, enigmatic, variably present components of several teleost epithelia, have been regarded as normal cells of unknown function or parasites of unknown phylogeny. The present study examines rodlet cells in the northern creek chub, Semotilus atromaculatus, and the white sucker, Catostomus commersoni. In light microscopic histochemistry, rodlet cores give "RNA-type" reactions to acridine orange and methyl green – pyronin procedures, but in electon microscopy, application of the nuclease–gold procedure shows that rodlets contain DNA in a helical distribution at the core boundary, but not RNA. Rodlet cores also are labeled by S1 nuclease – gold, an enzyme that is specific for single-stranded DNA. We have concluded that DNA, and only DNA, is found in the rodlet, and that it occurs in a conformation not normally seen in the eukaryote nucleus. In fact, the rodlet with its DNA resembles no known eukaryote, prokaryote, or virus. Discussion includes the possibility that the rodlet core may be a natural example of DNA containing left-handed sequences (Z-DNA). Since the nucleus of the rodlet cell contains the same amount of DNA as nuclei of teleost cells, the cell itself is concluded to be of teleost origin, and the rodlets are proposed to be invasive structures of unknown phylogeny which convert the metabolism of the teleost cell to rodlet production.