NOVEL ROLES OF THE CILIARY GENES, THM1 AND THM2, IN ADIPOGENESIS, SKELETAL DEVELOPMENT, AND SPERMATOGENESIS

Abstract

Primary cilia are non-motile sensory organelles, which extend from the surface of most vertebrate cells. Mutations in ciliary genes result in a group of pleiotropic disorders termed ciliopathies, which can manifest obesity, skeletal abnormalities, and infertility. Previously, we identified THM1 as an intraflagellar transport Complex A protein essential for embryogenesis and post-natal tissue development and homeostasis. Here, we investigate novel roles for Thm1 and its uncharacterized paralog, Thm2. shRNA-mediated Thm1 knockdown in 3T3-L1 mouse pre-adipocytes reveals Thm1 deficiency increases adipogenesis and insulin sensitivity, providing an additional mechanism underlying Thm1-deficient obesity. Like THM1, THM2 localizes punctately along the ciliary axoneme, establishing THM2 as a ciliary protein. To determine a role for THM2, we generated two Thm2-null mouse lines - one using a construct from the knockout mouse project (KOMP) consortium, which has been backcrossed 5 generations onto a C57BL6/J background, and the other, using CRISPR/Cas9 genome editing which has been maintained on a mixed FVB/C57BL6/J background. Unexpectedly, Thm2-null mice on both backgrounds survive into adulthood with seemingly normal health. However, Thm2 deletion with an additional loss of one Thm1 allele on a C57BL6/J background at the 5th generation causes skeletal defects resulting in markedly smaller mice by post-natal day 14. On a mixed FVB/C57BL6/J background, Thm2-/-; Thm1aln/+ male mice appear healthy, but show a 44% decrease in fertility, accompanied by low sperm count, abnormal sperm flagella and sperm motility, and abnormal testis morphology, indicating defects in early sperm development. Thus, our studies establish novel roles for Thm1 and Thm2 in adipogenesis, skeletal development, and spermatogenesis and provide novel models to study molecular mechanisms underlying ciliopathies. These studies also establish functional interactions between Thm1 and Thm2.