Histone H3 Threonine Phosphorylation Regulates Asymmetric Histone Inheritance in the Drosophila Male Germline

Abstract

SUMMARY A long-standing question concerns how stem cells maintain their identity through multiple divisions. Previously we reported that pre-existing and newly synthesized histone H3 are asymmetrically distributed during Drosophila male germline stem cell (GSC) asymmetric division. Here we show that phosphorylation at Threonine 3 of H3 (H3T3P) distinguishes preexisting versus newly synthesized H3. Converting T3 to the unphosphorylatable residue alanine (H3T3A) or to the phosphomimetic aspartate (H3T3D) disrupts asymmetric H3 inheritance. Expression of H3T3A or H3T3D specifically in early-stage germline also leads to cellular defects including GSC loss and germline tumors. Finally, compromising the activity of the H3T3 kinase Haspin enhances the H3T3A but suppresses the H3T3D phenotypes. Together these studies demonstrate that H3T3P distinguishes sister chromatids enriched with distinct pools of H3, coordinating asymmetric segregation of “old” H3 into GSCs, and that a tight regulation of H3T3 phosphorylation is required for male germline activity.

Preferential Phosphorylation on Old Histones during Early Mitosis in Human Cells

“…Further investigation is required to test these ideas. Intriguingly, a similar phenomenon was recently reported in the Drosophila male germ line (48,49), where the germ line stem cells (GSCs) undergo asymmetric cell division to generate one GSC and one differentiating daughter cell. Chen and coworkers (48) discovered that old/pre-existing canonical histone H3 but not H3.3 were selectively segregated to the daughter GSC.…”

“…Chen and coworkers (48) discovered that old/pre-existing canonical histone H3 but not H3.3 were selectively segregated to the daughter GSC. They further showed that H3T3ph was required for the asymmetric inheritance of H3, and they suggested it was required in a specific time window (prophase to metaphase) (49). The asymmetric cell division is only limited to Drosophila GSCs and is not seen in surrounding somatic tissues, so is the asymmetric distribution of H3T3ph and directional inheritance of histone H3 (48,49).…”

“…They further showed that H3T3ph was required for the asymmetric inheritance of H3, and they suggested it was required in a specific time window (prophase to metaphase) (49). The asymmetric cell division is only limited to Drosophila GSCs and is not seen in surrounding somatic tissues, so is the asymmetric distribution of H3T3ph and directional inheritance of histone H3 (48,49). However, the observations are highly similar to ours in this study that mitotic histone ph mark(s) is(are) enriched on the old histones in early mitosis, suggesting the underlying mechanism is conserved between Drosophila and humans.…”

Multifaceted Histone H3 Methylation and Phosphorylation Readout by the Plant Homeodomain Finger of Human Nuclear Antigen Sp100C

“…Sp100C Tolerates and Recognizes H3T3 PhosphorylationH3T3ph is a hallmark of chromosome segregation and contributes to asymmetric histone inheritance (25) as well as heritable epigenetic silencing (26). There exists a basic residue, Arg 713 , in the vicinity of H3T3 (Fig.…”

Choreography of parental histones in damaged chromatin

“…Noteworthy, newly synthesized histones H3 undergo a delay in mitotic phosphorylations associated with chromosome condensation, as shown in Drosophila and human cells. 24,25 We could then envision that the incorporation of new histones during DNA damage repair could interfere with chromosome condensation in early mitosis and thus serve as a "chromatin checkpoint" mechanism ensuring that incompletely repaired material cannot be transmitted to the next cell generation.…”