Add full taxonomy text.

descriptions/Zeng_Aging_Mouse_taxonomy.md

@@ -3,9 +3,14 @@
 The Mouse Aging dataset [Jin et al] is a comprehensive single-cell RNA
 sequencing (scRNA-seq) dataset containing ~1.2 million high-quality single-cell
 transcriptomes of brain cells from young adult and aged mice of both sexes,
-from regions spanning the forebrain, midbrain, and hindbrain. The 847 clusters
-identified in this dataset are presented here with mappings into the [Whole
-Mouse Brain Taxonomy](WMB-taxonomy.md).
+from regions spanning the forebrain, midbrain, and hindbrain. High-resolution
+de novo clustering of all cells results in 847 cell clusters and reveals at
+least 12 age-biased clusters that are mostly glial types. Clusters in the study
+were mapped to the Whole Mouse Brain taxonomy ([WMB-taxonomy](WMB-taxonomy.md))
+to provided class, subclass and supertype annotations. At the broader cell
+subclass and supertype levels, age-associated gene expression signatures were
+analyzed resulting in a list of 2,449 differentially expressed genes (age-DE
+genes) for many neuronal and non-neuronal cell types.
 
 The associated metadata is hosted on AWS S3 bucket as a AWS Public Dataset: