RNA binding protein RBM46 regulates mitotic-to-meiotic transition in spermatogenesis

Abstract

Meiosis entry during spermatogenesis requires reprogramming from mitotic to meiotic gene expression profiles. Transcriptional regulation has been extensively studied in meiosis entry, but gain of function for master transcription factors is insufficient to down-regulate mitotic genes. RNA helicase YTHDC2 and its partner MEIOC emerge as essential posttranscriptional regulators of meiotic entry. However, it is unclear what governs the RNA binding specificity of YTHDC2/MEIOC. Here, we identified RNA binding protein RBM46 as a component of the YTHDC2/MEIOC complex. Testis-specific Rbm46 knockout in mice causes infertility with defective mitotic-to-meiotic transition, phenocopying global Ythdc2 or Meioc knockout. RBM46 binds to 3′ UTR of mitotic transcripts within 100 nucleotides from YTHDC2 U-rich motifs and targets these transcripts for degradation. Dysregulated RBM46 expression is associated with human male fertility disorders. These findings establish the RBM46/YTHDC2/MEIOC complex as the major posttranscriptional regulator responsible for down-regulating mitotic transcripts during meiosis entry in mammalian spermatogenesis, with implications for understanding meiosis-related fertility disorders.

YTHDC2 serves a distinct late role in spermatocytes during germ cell differentiation

“…YTHDC2 may associate with specific protein complexes at different cell stages, leading to diverse, stage-specific molecular outcomes on RNA targets. Similar RBM46 IP Mass-spec experiments performed in P12 and P21 mouse testes revealed a number of RBM46-associated proteins, several of which were also present in the YTHDC2 protein complexes we identified, including MEIOC, PABPC1, MOV10 and UPF1 (Qian et al, 2022).…”

“…Our previous studies revealed that in Ythdc2 null mutant mice, a large number of germ cells underwent abnormal chromosome condensation soon after initiating meiotic prophase (Bailey et al, 2017), visible as abnormal metaphase-like spermatocytes in P12 testes. This phenotype was also observed in Meioc and Rbm46 knockout males (Abby et al, 2016;Qian et al, 2022;Soh et al, 2017). Quantification of testis tubule cross-sections revealed that only a small percentage of tubules in Ythdc2 cKO mice contained cells with condensed chromosomes.…”

“…Several studies have previously determined that YTHDC2 is part of a protein complex containing MEIOC (Abby et al, 2016; Bailey et al, 2017; Soh et al, 2017), the RNA-binding protein RMB46 (Li et al, 2022; Qian et al, 2022) as well as the exoribonuclease XRN1 (Kretschmer et al, 2018; Li et al, 2022; Wojtas et al, 2017). To elucidate the mechanism(s) of action of YTHDC2 during early and late meiotic prophase, we performed YTHDC2 immunoprecipitation experiments in P12 and P18 testis extracts, which revealed both RNA-independent and RNA-dependent YTHDC2 interacting partners in early and late spermatocytes.…”

“…Binding of YTHDC2 to both MEIOC and RBM46 does not require RNA. Meioc and Rbm46 knockout males show the same early spermatocyte death phenotype as Ythdc2 null mutants (Abby et al, 2016;Peart et al, 2022;Qian et al, 2022;Soh et al, 2017), suggesting that YTHDC2, MEIOC and RBM46 function together to regulate the switch from mitosis to meiosis in males. Directly tying YTHDC2 target RNAs to degradation machinery and supporting a functional role for YTHDC2 in regulating RNA stability, previous studies have also shown that the cytoplasmic 5ʹ → 3ʹ exoribonuclease XRN1 is a direct, RNA-independent binding partner of YTHDC2, interacting via the YTHDC2 ANK domain (Kretschmer et al, 2018;Li et al, 2022;Wojtas et al, 2017).…”

“…YTHDC2 protein contains two ankyrin (ANK) repeats, which typically mediate protein-protein interactions (Li et al, 2006). Previous studies have shown that YTHDC2 binds the meiotic protein MEIOC (Abby et al, 2016; Bailey et al, 2017; Li et al, 2022; Soh et al, 2017) as well as the RNA-binding protein RBM46 (Li et al, 2022; Qian et al, 2022). Binding of YTHDC2 to both MEIOC and RBM46 does not require RNA.…”