Early developmental arrest and impaired gastrointestinal homeostasis in U12-dependent splicing-defective Rnpc3-deficient mice

65K is an essential protein in adult mice and is necessary for the integrity of self-renewing tissues. The effect of acute, global 65K deficiency was studied in Rnpc3^lox/lox and Rnpc3^lox/+ adult mice (8–12 wk) harboring an inducible UBC-CreERT2 allele. These mice were weighed prior to tamoxifen treatment and daily thereafter. At the end of the experiment, tissues and peripheral blood were collected for analysis. (A) UBC-CreERT2;Rnpc3^lox/lox (green line, circles) mice had lost weight irreversibly by 6 d post-tamoxifen treatment and reached the ethical end-point requiring euthanasia at 8 d. In contrast, no significant weight loss was experienced by tamoxifen-treated UBC-CreERT2;Rnpc3^lox/+ mice (blue line, diamonds) or the three control strains: Rnpc3^lox/+ (blue line, inverted triangles), Rnpc3^lox/lox (red line, squares), and UBC-CreERT2 (red line, triangles). Data are expressed as mean + SEM (n = 3–9). (*) P < 0.05, two-way ANOVA with Tukey's multiple comparison testing. (B) Analysis of peripheral blood at 8 d post-tamoxifen treatment revealed a significant decrease in the numbers of white blood cells (WBC), lymphocytes, and monocytes in UBC-CreERT2;Rnpc3^lox/lox (green) compared to controls (red). (C) Red blood cell (RBC) numbers were also significantly decreased (D) and mice exhibited severe thrombocytopenia. (E) Systemic deletion of 65K induces thymic atrophy. Thymi were collected from control and UBC-CreERT2;Rnpc3^lox/lox mice at 8 d post-tamoxifen treatment and weighed. Data are expressed as mean + SEM (n = 7–9). (****) P < 0.0001, (***) P < 0.0002, (**) P < 0.01 Student's t-test. (F) Histological analysis of the thymus displays characteristic cortex (white arrow) and medulla (black arrow) regions in control animals (Rnpc3^lox/lox) at 8 d post-tamoxifen treatment. (G) This organization is absent in thymi taken from UBC-CreERT2;Rnpc3^lox/lox mice. Scale bar in F–G = 100 µm.