Dear Yongjun Kang, to avoid RNA smearing in 0.5X TBE native gels and achieve sharp, clear bands, focus on these key factors:

1. Prevent RNA Degradation by using RNase-free tools, gloves, and Diethyl pyrocarbonate (DEPC) -treated water to prevent RNA degradation from contamination.

2. Don't overload the gel with RNA,  use only 200-500 ng of RNA per well.

3. Run the gel at a low voltage (70-100 V) to prevent overheating, which can damage RNA.

4. Use freshly prepared 0.5X TBE buffer and ensure the gel and running buffer are well-mixed.

5. Purify your RNA and treat it with DNase if necessary to eliminate impurities.

6.  Stick to native loading dyes and avoid harsh chemicals like SDS.

Smearing is degraded RNA. The type of gel isn't important, most folks use a native (non-denaturing) agarose.

There are lots of ways to damage RNA: how was the tissue collected & stored, method of RNA extraction, RNA storage, RNA sample handling before loading gel, etc.

Can you rule out any of these possibilities? e.g. is the RNA a very old sample or one that is new? Did you keep the RNA on ice at all times?

Good luck!