Question: What is the general function of H3K79 methylation?

Context:
Saccharomyces cerevisiae cells lacking Dot1 exhibit a complete loss of H3K79 methylation and defects in heterochromatin-mediated silencing
Furthermore, an acidic patch at the C terminus of Dot1 is required for histone H4 tail binding in vitro, histone H3K79 di- and trimethylation in vivo, and proper telomere silencing
Recently, we demonstrated that in Drosophila spermatids, H3K79 methylation accompanies histone H4 hyperacetylation during chromatin reorganization
In human and mice spermatids, di- and tri-methylated H3K79 temporally overlapped with hyperacetylated H4 and thus accompanied chromatin reorganization.
Our results indicated that H3K79 methylation is a histone modification conserved in Drosophila, mouse, rat and human spermatids and may be a prerequisite for proper chromatin reorganization.
Here, we report the cytological distribution of the evolutionarily conserved DOT1L methyltransferase and the different H3K79 methylation states resulting from its activity (mono-, di- and tri-methylation; H3K79me1, me2 and me3, respectively) during meiotic prophase I in mouse spermatocytes. 
The heterochromatic centromeric regions and the sex body are enriched for H3K79me3
H3K79me patterns, combined with the cytological analysis of the H3.3, γH2AX, macroH2A and H2A.Z histone variants, are consistent with a differential role for these epigenetic marks in male mouse meiotic prophase I
We propose that H3K79me2 is related to transcriptional reactivation on autosomes during pachynema, whereas H3K79me3 may contribute to the maintenance of repressive chromatin at centromeric regions and the sex body.
We demonstrate that H3K79 dimethylation (H3K79me2) is converted to monomethylation (H3K79me1) at HOX loci as hematopoietic cells mature, thus coinciding with a decrease in HOX gene expression
H3K79 methylation: a new conserved mark that accompanies H4 hyperacetylation prior to histone-to-protamine transition in Drosophila and rat
Here we show for the first time that H3K79 methylation is a conserved feature preceding the histone-to-protamine transition in Drosophila melanogaster and rat.
The corresponding H3K79 methylation is a histone modification that precedes the histone-to-protamine transition and correlates with histone H4 hyperacetylation
In rat, H3K79 methylation also correlates with H4 hyperacetylation but not with active RNA polymerase II, which might point towards a conserved function in chromatin remodeling during the histone-to-protamine transition in both Drosophila and rat.
Methylation of histones H3 at positions K4 and K79 is involved in the initiation of recombination and the recombination checkpoint, respectively, during meiosis in the budding yeast. 
We confirmed the role of Set1-dependent H3K4 methylation in the formation of double-strand breaks (DSBs) in meiosis for the initiation of meiotic recombination, and we showed the involvement of Dot1 (H3K79 methylation) in DSB formation in the absence of Set1-dependent H3K4 methylation
Together, our studies identified the evolutionarily conserved YEATS domain as a novel acetyllysine-binding module and established a direct link between histone acetylation and DOT1L-mediated H3K79 methylation in transcription control.
Here, we unveil the role of Dot1-dependent histone H3 methylation at lysine 79 (H3K79me) in this meiotic surveillance mechanism.
Moreover, by genetically manipulating Dot1 catalytic activity, we find that the status of H3K79me modulates the meiotic checkpoint response.
Methylation of H3K79 is associated with chromatin at expressed genes, though it is unclear if this histone modification is required for transcription of all genes.
Thus, H3K79 methylation is not essential for transcription of Wnt-responsive or other intestinal genes, and intestinal toxicity is not imperative when DOT1L is rendered inactive in vivo.
Whereas mono-, di- and trimethylation states of lysines on histones typically have specific functions, no specific functions have been attributed so far to the different methylation states of histone H3 Lysine 79 (H3K79) generated by Dot1.
Indeed, gene silencing in yeast, which is dependent on Dot1, relied on global H3K79 methylation levels and not on one specific methylation state. Furthermore, our findings suggest that histone H2B ubiquitination affects H3K79 trimethylation by enhancing synthesis of all H3K79 methylation states. Our results suggest that multiple methylation of H3K79 leads to a binary code, which is expected to limit the possibilities for regulation by putative demethylases or binding proteins.
ChIP-chip analysis demonstrated histone H3 lysine 79 (H3K79) methylation profiles that correlated with Mll-AF4-associated gene expression profiles in murine ALLs and in human MLL-rearranged leukemias
To elucidate the mechanisms of genome reprogramming, we investigated histone H3 lysine 79 dimethylation (H3K79me2) and trimethylation (H3K79me3) in oocytes and preimplantation embryos via immunocytochemistry
n somatic cells and oocytes, H3K79me2 was observed throughout the genome, whereas H3K79me3 was localized in the pericentromeric heterochromatin regions in which there are no active genes.
Because H3K79me2 is considered an active gene marker, H3K79 methylation seems to have differing functions depending on the number of methyl groups added on the same residues. Both H3K79me2 and H3K79me3 decreased soon after fertilization, and the hypomethylated state was maintained at interphase (before the blastocyst stage), except for a transient increase in H3K79me2 at mitosis (M phase)
ChIP-chip tiling arrays revealed that levels of all degrees of genic H3K79 methylation correlate with mRNA abundance and dynamically respond to changes in gene activity.
Conversion of H3K79 monomethylation into di- and trimethylation correlated with the transition from low- to high-level gene transcription. We also observed enrichment of H3K79 monomethylation at intergenic regions occupied by DNA-binding transcriptional activators. Our findings highlight several similarities between the patterning of H3K4 methylation and that of H3K79 methylation in mammalian chromatin, suggesting a widespread mechanism for parallel or sequential recruitment of DOT1L and MLL to genes in their normal "on" state.
URA3 reporter assays also indicated that H3K79 methylation is required for HM silencing. Surprisingly, a genome-wide expression analysis of H3K79 methylation-defective mutants identified only a few telomeric genes, such as COS12 at TEL-VII-L, to be subject to H3K79 methylation-dependent natural silencing.
Furthermore, H3K79 methylation by Dot1 did not play a role in the maintenance of natural HML silencing
Since the discovery ∼10 years ago that Dot1 and its mammalian homolog, DOT1L (DOT1-Like), possess histone methyltransferase activity toward histone H3 Lys 79, great progress has been made in characterizing their enzymatic activities and the role of Dot1/DOT1L-mediated H3K79 methylation in transcriptional regulation, cell cycle regulation, and the DNA damage response
The histone 3 lysine 79 (H3K79) methyltransferase Dot1l has been implicated in the development of leukemias bearing translocations of the Mixed Lineage Leukemia (MLL) gene
Inhibition of histone H3K79 methylation selectively inhibits proliferation, self-renewal and metastatic potential of breast cancer
H3K79 methylation directly precedes the histone-to-protamine transition in mammalian spermatids and is sensitive to bacterial infections
in Drosophila spermatids, H3K79 methylation accompanies histone H4 hyperacetylation during chromatin reorganization
In human and mice spermatids, di- and tri-methylated H3K79 temporally overlapped with hyperacetylated H4 and thus accompanied chromatin reorganization
Our results indicated that H3K79 methylation is a histone modification conserved in Drosophila, mouse, rat and human spermatids and may be a prerequisite for proper chromatin reorganization
During spermiogenesis, haploid spermatids undergo extensive chromatin remodeling events in which histones are successively replaced by more basic protamines to generate highly compacted chromatin. Here we show for the first time that H3K79 methylation is a conserved feature preceding the histone-to-protamine transition in Drosophila melanogaster and rat
When acetylation was inhibited in cultured Drosophila testes, nuclei were smaller and chromatin was compact, Gpp was little synthesized, H3K79 methylation was strongly reduced, and protamines were not synthesized
Deficiency of H3K79 histone methyltransferase Dot1-like protein (DOT1L) inhibits cell proliferation
Dot1-like protein (DOT1L) is an evolutionarily conserved histone methyltransferase that methylates lysine 79 of histone H3 (H3K79). Mammalian DOT1L participates in the regulation of transcription, development, erythropoiesis, differentiation, and proliferation of normal cells
H3K79 methylation is a critical histone modification that regulates cell proliferation and would be a novel histone mark for aging and cancer
In rat, H3K79 methylation also correlates with H4 hyperacetylation but not with active RNA polymerase II, which might point towards a conserved function in chromatin remodeling during the histone-to-protamine transition in both Drosophila and rat

Answer: ChIP-chip tiling arrays revealed that levels of all degrees of genic H3K79 methylation correlate with mRNA abundance and dynamically respond to changes in gene activity. 
ChIP-chip tiling arrays revealed that levels of all degrees of genic H3K79 methylation correlate with mRNA abundance and dynamically respond to changes in gene activity. Conversion of H3K79 monomethylation into di- and trimethylation correlated with the transition from low- to high-level gene transcription. Findings highlight several similarities between the patterning of H3K4 methylation and that of H3K79 methylation in mammalian chromatin.
Methylation of H3K79 is associated with chromatin at expressed genes, though it is unclear if this histone modification is required for transcription of all genes.
H3K79 methylation is a histone modification that correlates with histone H4 hyperacetylation prior to histone-to-protamine transition, and is accompanied by chromatin reorganization, playing an important role in the regulation of cell proliferation.