In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: Molecularly , ANF mRNA increased 250 % and SERCA2 mRNA decreased 57 % .
### Output Text:
Molecularly , ANF mRNA increased 250 % and SERCA2 mRNA decreased 57 % . 