Fixation and immunolocalization of left-handed Z-DNA sequences in the calf lens

In order to establish the presence of Z-DNA sequences in the normal crystalline lens and to define their structure-function relationship, fixed and unfixed calf lens tissue sections were examined immunohistochemically. Polyclonal and monoclonal anti-Z-DNA antibodies were developed as immunoprobes, using brominated (Br-) poly(dG-dC).poly(dG-dC) as an antigen. The structure of the Z-helix antigen was confirmed by circular dichroism (CD) and U.V. spectroscopy. Whole rabbit and goat anti-Z-DNA sera; rabbit and goat IgG polyclonal anti-Z-DNA antibodies; and anti-Z-DNA monoclonal IgG antibodies were utilized as Z-DNA immunoprobes to localize the Z-DNA in calf lens tissue sections. Immunohistochemical examination using the peroxidase-antiperoxidase (PAP) method indicated that the cortex region of the lens reacted strongly with the anti-Z-DNA antibodies, while no immunoreaction could be observed in the nucleus region. Similar immunoreactive patterns were obtained whether whole sera, affinity purified IgG polyclonal antibodies or monoclonal antibodies were utilized. Immunobinding of anti-Z-DNA antibodies was low, effectively background type binding, in unfixed lens tissue sections. Various fixatives were tested to explore the potential antibody-Z-DNA interaction in calf lens tissue. Nuclear fixatives enhanced Z-DNA antibody immunoreactivity, while formalin, microanatomic and cytoplasmic fixatives produced lesser results. Digestion of the lens tissue with DNase I eliminated Z-DNA immunoreactivity, while RNase A and RNase T1 treatment had no effect. Actinomycin D also prevented Z-DNA immunoreactivity.