FIG. 5.

Insulin is impermeable to the blood-testis barrier. A: FITC-labeled insulin injected into the interstitium of wild-type (WT) mice does not penetrate the blood-testis barrier (n = 3). B: The blood-testis barrier in Akita homozygotes also restricts passage of insulin across the barrier. C: PBS-injected control demonstrates no autofluorescence. D: Experimental controls: FITC-insulin is increasingly restricted to the interstitium as the blood-testis barrier forms in developing mice; interstitial staining is seen at p7 and p9. By p12, the barrier has formed and is intact, thus preventing passage of interstitially injected FITC-labeled insulin. (A high-quality digital representation of this figure is available in the online issue.)