Lessons from a gene knockout mouse model: no phenotypes induced by deletion of the TPR4 domain of Ttc22

The TTC22 gene encodes a protein containing seven tetratricopeptide repeats (TPRs), which mediate protein-protein interactions as chaperones. We previously reported that the level of TTC22 transcript variant 1 (TTC22v1) was downregulated in human colon adenocarcinoma (COAD) and that TTC22 upregulated m6A-mediated WTAP and SNAI1 expression via the TTC22-RPL4 interaction and subsequently promoted COAD metastasis. Thus, a commercially available C57BL/6N mouse model in which the Ttc22 exon 2&3 encoding the TPR4 (equal to the human TTC22 TPR3) domain was knocked out via CRISPR-Cas9 was used to evaluate the contribution of Ttc22 to the development of mice and COAD. To determine the status of Ttc22 expression in Ttc22 knockout mice, we prepared a rabbit polyclonal antibody against the mouse Ttc22 protein, which could bind both wild type Ttc22 and TPR4-deleted Ttc22 proteins overexpressed in HEK293T cells, as determined by Western blot analysis. Ttc22 proteins were detected in colon tissue samples from wild-type mice and Ttc22 hemi-knockout (Ttc22-/+) mice but not in those from fully Ttc22 knockout (Ttc22-/-) mice. Unfortunately, the long-term observation results demonstrated that Ttc22 knockout (KO, including Ttc22-/+ or Ttc22-/-) did not affect the body weight, development, fertility, or spontaneous tumor incidence of male or female mice. No differences in the incidence of AOM/DSS-induced COAD were observed between these mouse groups, although Ttc22 deletion partially resulted in the upregulation of genes related to the host adaptive response to inflammation in the colon mucosa. In conclusion, no phenotypes were induced by Ttc22 inactivation in C57BL/6N mice.