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: Using puromycin aminonucleoside nephrosis ( PAN ) rats , we studied early ultrastructural and permeability changes in relation to the expression of the podocyte - associated molecules nephrin , a - actinin , dendrin , and plekhh2 , the last two of which were only recently discovered in podocytes .
### Output Text:
Using <span class="chemical">puromycin aminonucleoside</span> nephrosis ( PAN ) rats , we studied early ultrastructural and permeability changes in relation to the expression of the podocyte - associated molecules nephrin , a - actinin , dendrin , and plekhh2 , the last two of which were only recently discovered in podocytes . 