Given a Specimen Tag, retrieve RNA-seq experiment, genes and expression levels. A Specimen Tag is an identifier that we assign to BioSamples from the same individual/tissue that were used in different types of experiments (e.g. RNA-seq, ChIP-seq, ATAC-seq). Sometimes the Specimen Tag is equivalent to the BioSample id. However when specimens from the same individual/tissue were submitted as a different BioSample for each type of experiment, we assign an identifier that combines the tissue and individual id so that the combined results for this individual/tissue can be investigated.