Normal development of the mouse mammary gland. (a) Schematic of distinct stages of development and characteristic biological processes. Shown are time points used for mRNA expression profiling (time point 12 hours involution was used for miRNA expression profiling only, time points 8 weeks and 10 days lactation were used for mRNA expression profiling only). (b-c) Mean relative log2 mRNA expression for non-redundant Gene Ontology biological processes (b) and KEGG pathways (c) (shown are gene sets with at least 100 genes represented on the array, numbers of genes are indicated in brackets). Red and blue indicate high and low relative log2 expression, respectively. (d) Representative H&E stained histological sections of mouse mammary glands obtained at distinct time points during development and used for expression analysis.