Expression of the Tg(Cldn11)605Gow transgene in testis. Testes from mice harboring 2 (+/+), 1 (+/−), or 0 (−/−) copies of the wild-type Cldn11 gene as well as testes from transgenic mice (lines 5, 8–11, and 12) were dissected at 2 mo of age for Southern blotting with a Cldn11 cDNA probe (a), Northern blotting with a Cldn11 cDNA probe (b), and Western blotting with antibodies against CLDN11 (upper) and β-actin (lower; c). d) We observe a strong and highly statistically significant Spearman correlation coefficient between transgene copy number determined from Southern blots and steady-state expression level from Northern blots (r = 0.94; P = 0.0004). Lines 9 and 10 have the lowest transgene copy numbers, with expression levels similar to Cldn11+/− mice, but synthesize very low levels of CLDN11. Indeed, the apparent level of CLDN11 in lines 5, 8, 11, and 12 is unexpectedly low compared to steady-state mRNA levels, for unknown reasons, and approximates the level of protein in wild-type testis.