SSC Niche and SSC In Zebrafish Figure 1. Topographical distribution of type A undifferentiated spermatogonia in zebrafish testes. A. Quantification of type A undifferentiated spermatogonia as located near the interstitium or in the intertubular area. Note that ,76% of type A undifferentiated spermatogonia are preferentially located near the interstitium. B. Tubular perimeter of the regions contacting the interstitium or intertubular areas. A,B. Bars represent the mean 6 SE which are expressed as percentage. Different letters mean significant differences among the groups. C,D. Histological sections of the zebrafish seminiferous tubules. Note that most of type A undifferentiated spermatogonia (arrowheads) are distributed near the (yellow) interstitium. Staining: PAS (Periodic Acid Schiff)/Ferric Hematoxylin/Metanil Yellow. Scale bar = 10 mm. E. Relative number of type Aund* and Aund in normal (n = 7) and busulfan-depleted testes (n = 10). Bars represent the percentage mean 6 SE of 100–200 type A spermatogonia, significant differences among the groups (p,0.05) are indicated by an asterisk. doi:10.1371/journal.pone.0012808.g001 http://www.gehealthcare.com) (2 mCi/g/BW), and were sacri- ficed at 2 h, 12 h, 1, 2, 3, 4, 5 and 6 days after thymidine injection. Testes were weighed for calculating the gonadosomatic index (GSI = testes weight/body weight 6100), fixed, embedded and sectioned as above, and prepared for autoradiographic analysis to estimate the duration of meiosis and spermiogenesis as described previously [16,29]. Based on these results (Figure S1), 35uC was chosen as optimal temperature to deplete endogenous zebrafish PLoS ONE | www.plosone.org 3 September 2010 | Volume 5 | Issue 9 | e12808