SGM Journals

Research explained · Microscopy methods

Why can a DNA stain miss DNA in a cell?

A DNA stain can miss DNA when the dye cannot reach the cell interior or when the resulting light is too weak to detect. In Kerala’s red rain cells, the same dye gave no detectable signal before pigment removal and a blue signal in the cell center after treatment. [1][2]

See original studies View the SGM research record

Where a fluorescence test can fail

Dye access
Can the dye reach the material inside the cell?
Compare treated and untreated samples with the same stain. In the Kerala experiment, the signal appeared after solvent treatment. [1]
Dye binding
What does the dye bind to under these conditions?
Check how the dye behaves with the expected target. Lab work found that DAPI interacted differently with model DNA and RNA sequences. [2]
Signal detection
Can the instrument see the expected light against the background?
Include a known positive and a background comparison. The 2006 study showed a positive signal in yeast even though the red rain mixture did not give one. [3]

What did Figure 5 show?

Gangappa and Hogg exposed the stained preparations to 405-nanometer light. Untreated cells produced no detectable signal under those conditions. After treatment with dimethyl sulfoxide (DMSO), the cell centers emitted blue light at 461 nanometers, consistent with DAPI bound to DNA. Compare panels B and D on page 110. [1]

Why isn’t a yeast comparison enough?

It shows that the dye and instrument can produce a detectable result in yeast. It cannot tell you whether the same preparation exposes DNA in an unfamiliar particle. Work on bacterial endospores is another example of why the properties of the sample matter when using fluorescent dyes. The comparison is about how stains behave, while the identity of the Kerala particles is a separate question. [1][3][4]

Can fluorescence identify the species?

A fluorescent stain can reveal where a signal appears inside a cell. A species identification requires other evidence, such as an informative DNA sequence compared with reference sequences. In the Kerala experiment, the microscope result addressed whether DNA was present in the tested cells. [1]

Original research

  1. Gangappa and Hogg (2013), Microbiology. DNA unmasked in the red rain cells of Kerala. Figure 5 compares the fluorescent signal in treated and untreated cells.
  2. Tanious et al. (1992), Biochemistry. DAPI binds differently to DNA and RNA. Compares DAPI’s interaction with model DNA and RNA sequences.
  3. Louis and Kumar (2006), Astrophysics and Space Science. The Red Rain Phenomenon of Kerala and its Possible Extraterrestrial Origin. Section 9 and Figure 15 document the earlier dye test.
  4. Laflamme et al. (2004), Journal of Applied Microbiology. Assessment of bacterial endospore viability with fluorescent dyes. Studies how fluorescent dyes behave in bacterial endospores.