SAGE analysis of prostatic inductive mesenchyme. (a) The strategy used in construction and comparison of serial analysis of gene expression (SAGE) libraries to identify ventral mesenchymal pad (VMP) specific or enriched transcripts. P0 female urogenital tracts (UGTs) were microdissected to provide either pure VMP or the whole prostatic rudiment (VMP, smooth muscle, urethral epithelium [VSU]); the tissues dissected for library construction are outlined in black. The VMP tissue comprised only the condensed inductive mesenchyme of the VMP, whereas the VSU library contained urethral epithelium, smooth muscle, urethral mesenchyme and VMP. Both VMP and VSU SAGE libraries were sequenced to the indicated total number of tags. Pair-wise comparison was performed and 219 tags exhibiting statistically significant enrichment in the VMP were identified. (b) Scatter plot showing the comparison of the VMP and VSU SAGE libraries. Tag frequencies were plotted on a logarithmic scale and P values were calculated using the Z test; tags showing a difference at P = 0.05 are shown in red. (c) Pie chart depicting functional classification of the 219 VMP identified transcripts; extracellular (EC) signaling modulators and hypothetical proteins were highlighted for further analysis. Bl, bladder; TF, transcription factors; Ur, urethra; Ut, uterus; Vg, vagina; VMP, ventral mesenchymal pad.