Clusters of gene expression profiles from a 12-point time course of adult mammary gland development. Thirty-five K means clusters were obtained from 6796 differentially expressed genes across a 12-point time course of the adult mammary gland pregnancy cycle. In order to identify basic trends in expression, these clusters were arbitrarily organized into groups based on the similarity between their mean profiles (b). These clusters were pooled and displayed as combined average expression profiles (a). (a) Combined expression profiles named according to developmental stage exhibiting maximal expression (capital) and their associated expression pattern (subscript). VSL, virgin and suppressed lactation; G, gestation; GSL, gestation and suppressed lactation; LT, lactation, transient; L, lactation; LG, lactation and gestation; IL, involution and lactation; IT, involution, transient; IP, involution and parturition; IG, involution and gestation; PC, postcoitum. Y axis is the mean normalized signal intensity. Dotted lines indicate boundaries between major phases of development: virgin to gestation; parturition; and 10-day lactation (forced weaning). Total number of genes in each combined cluster shown to the right. (b)Thirty-five K-means clusters. Total number of genes (brackets) and the ID for each cluster is shown. Each differentially expressed transcript is represented only once in the 35 clusters. Error bars represent standard error of the mean. X axis is the 12 developmental time points used in microarray analysis: v, virgin (8 week); G, gestation (days 5, 10 and 15 postcoitum); L, lactation (days 0, 5 and 10 postpartum); I, involution (days 0.5, 1, 2, 3 and 4 after forced weaning).