Abstract
TTLL5/STAMP (tubulin tyrosine ligase-like family member 5) has multiple activities in cells. TTLL5 is one of 13 TTLLs, has polyglutamylation activity, augments the activity of p160 coactivators (SRC-1 and TIF2) in glucocorticoid receptor-regulated gene induction and repression, and displays steroid-independent growth activity with several cell types. To examine TTLL5/STAMP functions in whole animals, mice were prepared with an internal deletion that eliminated several activities of the Stamp gene. This mutation causes both reduced levels of STAMP mRNA and C-terminal truncation of STAMP protein. Homozygous targeted mutant (Stamp(tm/tm)) mice appear normal except for marked decreases in male fertility associated with defects in progressive sperm motility. Abnormal axonemal structures with loss of tubulin doublets occur in most Stamp(tm/tm) sperm tails in conjunction with substantial reduction in α-tubulin polyglutamylation, which closely correlates with the reduction in mutant STAMP mRNA. The axonemes in other structures appear unaffected. There is no obvious change in the organs for sperm development of WT versus Stamp(tm/tm) males despite the levels of WT STAMP mRNA in testes being 20-fold higher than in any other organ examined. This defect in male fertility is unrelated to other Ttll genes or 24 genes previously identified as important for sperm function. Thus, STAMP appears to participate in a unique, tissue-selective TTLL-mediated pathway for α-tubulin polyglutamylation that is required for sperm maturation and motility and may be relevant for male fertility.
Highlights
Ttll5/STAMP is a multifunctional protein in cells with unknown activity in animals
For more precise identification of Ttll5/Stamp-expressing cell types, we performed in situ hybridization assays
We chose to target STAMP activities because the ϳ200-amino acid size of just the TTLL domain of Ttll5 is encoded by 10 exons spanning 82 kb, which is too much to remove by targeted deletion techniques
Summary
Ttll5/STAMP is a multifunctional protein in cells with unknown activity in animals. Results: Targeted disruption of the Ttll5/Stamp gene in mice causes male infertility with reduced ␣-tubulin polyglutamylation and axoneme disruption in sperm. In view of the assorted activities of TTLL5/STAMP in vitro, it was of interest to know the physiological role(s) of TTLL5/ STAMP in vivo For this reason, we generated mice with a Ttll5/ Stamp gene that would be functionally defective for modulating the properties of STAMP, i.e., steroid receptor regulated gene transcription, while retaining the TTL domain and its glutamylation activities. We generated mice with a Ttll5/ Stamp gene that would be functionally defective for modulating the properties of STAMP, i.e., steroid receptor regulated gene transcription, while retaining the TTL domain and its glutamylation activities This deletion causes a decrease in all forms of TTLL5/STAMP mRNA. Additional studies suggest that these unique defects in spermatogenesis and sperm motility are due not to the expected steroidogenic pathways but rather to structural defects in the sperm caused by reduced levels of the truncated mRNAs and resulting polyglutamylation activity
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