Before moving to UT Southwestern, Mendell was a Howard Hughes Medical Institute early career scientist[1] at Johns Hopkins School of Medicine.
He remained at Johns Hopkins as a faculty member before moving to University of Texas Southwestern Medical Center in 2011.
As a graduate student with Harry (Hal) Dietz at Johns Hopkins, Mendell researched how cells recognize and degrade messenger RNA molecules with early stop codons, a process known as nonsense mediated decay.
[1] In 2005, Mendell reported in the journal Nature that a gene often mutated in cancer cells, c-Myc, influences the expression of several miRNAs encoded in a cluster on human chromosome 13.
In 2009, Mendell reported in the journal Cell that treating mice with therapeutic levels of specific miRNAs could suppress development of liver cancer.