Gene ontology (GO) category enrichment in the differentially up-regulated gene clusters present in pre-pubertal and pubertal germ cells and Sertoli cells. (A) Gene ontology categories for transcripts enriched or attenuated in G9 and S9 cells. Number of transcripts associated with a specific GO category and enriched in a cluster are given within rectangles as observed and as expected values. For each GO category, P values are shown by a gradual color code bar. Red indicates over-representation of transcripts in a GO category whereas blue specifies under-representation. The gene sets up-regulated in one condition (as defined in Figure 2B) were analyzed here for GO enrichment and ordered according to the peak expression found in pre-pubertal (G9) and pubertal (G22) germ cells and in Sertoli cells (S9 and S22). Only the most enriched GO categories are displayed here for the four cell populations. (B) Validation of Spga and Sertoli cell specific gene expression at pre-puberty by RT-PCR. Expression of Polo-like kinase 2 (plk2), growth associated protein 43 (gap43) and pancreatitis associated protein 3 (pap3) in prepubertal (9 dpp) and pubertal (22 dpp) spermatogonia and Sertoli cells (G9, G22. S9, S22, respectively) was quantified by real time RT-PCR. Values normalized to the housekeeping genes ubc are shown; the same pattern was observed when normalizing with the expression of ps9, the other housekeeping gene (not shown). Shown are the mean values (± SEM) from the 3 distinct cell preparations, for which genome-wide analysis by hybridization to a high density array is shown in Figure 2.