A CUG-initiated CATSPERθ functions in the CatSper channel assembly and serves as a checkpoint for flagellar trafficking

Abstract

Calcium signaling is critical for successful fertilization. In spermatozoa, calcium influx into the sperm flagella mediated by the sperm specific CatSper calcium channel is necessary for hyperactivated motility and male fertility. CatSper is a macromolecular complex and is repeatedly arranged in zigzag rows within four linear nanodomains along the sperm flagella. Here, we report that theTmem249-encoded transmembrane domain containing protein, CATSPERθ is essential for the CatSper channel assembly during sperm tail formation. CATSPERθ facilitates the channel assembly by serving as a scaffold for a pore forming subunit CATSPER4. CATSPERθ is specifically localized at the interface of a CatSper dimer and can self-interact, suggesting its potential role in CatSper dimer formation. Male mice lacking CATSPERθ are infertile because the sperm lack the entire CatSper channel from sperm flagella, rendering sperm unable to hyperactivate, regardless of their normal expression in the testis. In contrast, genetic abrogation of any of the other CatSper transmembrane subunits results in loss of CATSPERθ protein in the spermatid cells during spermatogenesis. CATSPERθ might acts as a checkpoint for the properly assembled CatSper channel complex to traffic to sperm flagella. This study provides insights into the CatSper channel assembly and elucidates the physiological role of CATSPERθ in sperm motility and male fertility.

The Role of Sperm Membrane Potential and Ion Channels in Regulating Sperm Function

“…The cation channel of sperm, CatSper, is a sperm-specific voltage- and pH-dependent calcium channel localized in the principal piece of sperm flagellum [ 151 , 162 ]. CatSper belongs to the family of voltage-gated Ca 2+ channels and is the main channel responsible for Ca 2+ influx in mammalian sperm [ 14 , 155 , 156 , 157 , 158 , 159 , 160 , 161 , 162 , 163 , 164 , 165 , 166 , 167 , 168 , 169 , 170 , 171 , 172 , 173 , 174 , 186 , 187 , 188 , 189 , 190 ]. CatSper channels comprise four homologous pore-forming α subunits named CATSPER1, CATSPER2, CATSPER3 and CATSPER4 [ 15 , 24 , 25 , 151 , 155 , 162 , 166 ].…”

“…Very recently, new subunits of this highly complex channel, which has been named CatSpermasome, have been characterized. Lin et al (2021) and Huang et al (2023) described three new components in mouse sperm: the transmembrane protein 249 (TMEM249), now named CATSPERθ, essential for the CatSper channel assembly during sperm tail formation; the transmembrane protein 262 (TMEM262), which has been named CATSPERŋ, and the rodent- and testis-specific solute carrier organic anion transporter SCLO6C1 [ 159 , 190 ]. These proteins interact with other auxiliary transmembrane proteins of CatSper (CATSPERŋ with CATSPERβ and SCLO6C1 with CATSPERε) and contribute to the assembly and stability of the CatSper complex [ 159 ].…”

The Cation/Calcium Channel of Sperm (CatSper): A Common Role Played Despite Inter-Species Variation?

“…On the other hand, CatSper 1 and 2 are downregulated in heat-stressed rat sperm cells, perhaps in relation to the well-recognized impairment of spermatogenesis by increased temperature [ 58 ]. Interestingly, Tmem249 uniquely uses a CTG start codon to encode CATSPERθ, the latter stabilizing the CATSPER4 subunit and its conformational ordering [ 59 ].…”

The Chemosensing Role of CatSper in Mammalian Sperm: An Updated Review

“…CatSper is located in the flagellar principal piece [ 7 ]. The CatSper complex consists of four pore-forming alpha subunits (CATSPER1–4) and at least eight auxiliary subunits (CATSPERβ, γ, δ, ε, ζ, and θ [ 10 ]; EF-hand calcium binding domain 9; and C2 calcium dependent domain containing 6 [ 11 ]) [ 12 , 13 ]. These subunits are conserved between mouse and human, and genetic variations in CATSPER1 , CATSPER2 , CATSPER3 , and CATSPERE have been found in infertile men [ 14 , 15 , 16 ].…”