The PHD finger protein Spp1 has distinct functions in the Set1 and the meiotic DSB formation complexes

Abstract

Histone H3K4 methylation is a feature of meiotic recombination hotspots shared by many organisms including plants and mammals. Meiotic recombination is initiated by programmed double-strand break (DSB) formation that in budding yeast takes place in gene promoters and is promoted by histone H3K4 di/trimethylation. This histone modification is recognized by Spp1, a PHD finger containing protein that belongs to the conserved histone H3K4 methyltransferase Set1 complex. During meiosis, Spp1 binds H3K4me3 and interacts with a DSB protein, Mer2, to promote DSB formation close to gene promoters. How Set1 complex- and Mer2- related functions of Spp1 are connected is not clear. Here, combining genome-wide localization analyses, biochemical approaches and the use of separation of function mutants, we show that Spp1 is present within two distinct complexes in meiotic cells, the Set1 and the Mer2 complexes. Disrupting the Spp1-Set1 interaction mildly decreases H3K4me3 levels and does not affect meiotic recombination initiation. Conversely, the Spp1-Mer2 interaction is required for normal meiotic recombination initiation, but dispensable for Set1 complex-mediated histone H3K4 methylation. Finally, we provide evidence that Spp1 preserves normal H3K4me3 levels independently of the Set1 complex. We propose a model where Spp1 works in three ways to promote recombination initiation: first by depositing histone H3K4 methylation (Set1 complex), next by “reading” and protecting histone H3K4 methylation, and finally by making the link with the chromosome axis (Mer2-Spp1 complex). This work deciphers the precise roles of Spp1 in meiotic recombination and opens perspectives to study its functions in other organisms where H3K4me3 is also present at recombination hotspots.

CXXC1 is redundant for normal DNA double-strand break formation and meiotic recombination in mouse

“…Several reports have shown that Spp1, the yeast ortholog of CXXC1, binds to H3K4me3 and tethers H3K4-trimethylated recombination hotspots to the chromosome axis [17–19]. To test whether CXXC1 binds to H3K4me3 in mouse spermatocytes, we performed CXXC1 co-IP from B6 testicular extract.…”

“…The yeast CXXC1 ortholog Spp1 is a key player in recombination by linking H3K4me3 sites with the chromosome axis and connecting them with the recombination protein Mer2 [17–19]. These observations suggested that CXXC1 might play similar function in mammalian meiosis.…”

“…Spp1 is predominantly located on the chromosome axes and connects H3K4 trimethylated sites with the axis protein Mer2 to stimulate Spo11 dependent DSB formation [17,18]. Recent study showed that Spp1 function in tethering DSB sites to chromosome axes and ensuring efficient DSB formation is independent of its function as a COMPASS complex member [19].…”

CFP-1 interacts with HDAC1/2 complexes inC. elegansdevelopment

“…Furthermore, we found that a decrease in deacetylase activity enhances the low brood phenotype of cfp-1(tm6369) mutant suggesting that CFP-1 might cooperate with HDACs for deacetylase activity. Previous study in yeast has shown that Spp1 (yeast ortholog of cfp-1) exist in Mer2-Spp1 complex (Adam et al, 2018). It could be possible that CFP-1 is also present in HDAC complexes.…”

Delineation of the SUMO-Modified Proteome Reveals Regulatory Functions Throughout Meiosis

“…Intriguingly, two key regulatory DSB factors, Spp1 and Mer2, were SUMOylated at multiple sites (Figure 6B). Spp1 reads H3K4 trimethylation marks using its PHD finger and recruits DSB hotspots to the axis via an interaction with Mer2 (Acquaviva et al, 2013;Adam et al, 2018;Sommermeyer et al, 2013). Mer2 IHO1 is recruited to axes via Red1 and Hop1, where its cell cycle and replication-dependent phosphorylation leads to association with other DSB factors, Rec114-Mei4 and Xrs2, to trigger DSB formation only on replicated sister chromatids (Lam and Keeney, 2014).…”