Figure 3

LIN28 is specifically expressed in undifferentiated spermatogonia. Whole-mount immunofluorescence of seminiferous tubules from adult mice was performed with anti-LIN28 antibody. (A) Whole-mount examination of LIN28 expression in seminiferous tubules. Examples of A_s, A_pr, and A_al (up to 32 interconnected cells) spermatogonia are shown. LIN28 is predominantly cytoplasmic with punctate nuclear staining. Note that the A_pr and A_al spermatogonia are interconnected by intercellular cytoplasmic bridges due to incomplete cytokinesis. The background fluorescence helps orient the tubules. Scale bars, 25 μm. (B) Frequency of spermatogonia clusters comprising different numbers of chained LIN28-positive cells. A total of 205 isolated cells and clusters were counted. Only clearly identified clusters were included. The percentage of clusters with a longer chain of cells might be underestimated, since such large clusters extended around the tubule edge as shown in Fig. 3A and thus were excluded. Clusters with a non-2ⁿ number of cells or too many chained cells were grouped as "other".