Swiss 3T3 after serum starvation

[Sin Wun Chey]

Hello everyone,
I hope someone can tell me what I saw.
When Swiss 3T3 cell was serum starved from 2 days, there was a ring of 
non-transparent material(under ordinary light microscope) around the 
nucleus. It had multiple projections and this star-like structure can 
extend throughout the cell as though forming a network, stopping short of 
the plasma membrane. It is definitely not actin or tubulin (from 
immunostaining).
In contrast, a cell happily in serum containing medium does not have this 
aggregation and the cytoplasm appears homogenous under low power light 
microscope.
I am not a cell biologist and would be grateful for any answers/suggestions.

Thanks.