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: Moreover , AT2R gene and protein expressions in fetal kidneys were inhibited by PCE , associated with the repression of the gene expression of glial - cell - line - derived neurotrophic factor ( GDNF ) / tyrosine kinase receptor ( c - Ret ) signaling pathway .
### Output Text:
Moreover , AT2R gene and protein expressions in fetal kidneys were inhibited by PCE , associated with the repression of the gene expression of glial - cell - line - derived neurotrophic factor ( GDNF ) / <span class="chemical">tyrosine</span> kinase receptor ( c - Ret ) signaling pathway . 