Dido3-dependent HDAC6 targeting controls cilium size.

Primary cilia are involved in a variety of physiological processes such as sensing of the environment, cell growth and development. Numerous developmental disorders and pathologies arise from defects in these organelles. Multiple proteins that promote formation and disassembly of the primary cilium have been identified, but little is known about the mechanisms that control steady-state cilium size. Here, we show that death inducer obliterator (Dido3)-dependent targeting of histone deacetylase 6 (HDAC6) is a key determinant of cilium size in growth-arrested cells. The amount of either protein negatively correlates with cilium size. Dido3 availability at the centrosome governs ciliary HDAC6 levels, and redistribution of the two proteins controls tubulin acetylation. In turn, basal body localization of Dido3 and HDAC6 depends on the actin network, previously shown to limit cilium size independent of the cell cycle. These results show that not only kinase-dependent activation of a deacetylase but also its subcellular distribution controls substrate selection.

Synaptonemal complex assembly and H3K4Me3 demethylation determine DIDO3 localization in meiosis.

Synapsis of homologous chromosomes is a key meiotic event, mediated by a large proteinaceous structure termed the synaptonemal complex. Here, we describe a role in meiosis for the murine death-inducer obliterator (Dido) gene. The Dido gene codes for three proteins that recognize trimethylated histone H3 lysine 4 through their amino-terminal plant homeodomain domain. DIDO3, the largest of the three isoforms, localizes to the central region of the synaptonemal complex in germ cells. DIDO3 follows the distribution of the central region protein SYCP1 in Sycp3-/- spermatocytes, which lack the axial elements of the synaptonemal complex. This indicates that synapsis is a requirement for DIDO3 incorporation. Interestingly, DIDO3 is missing from the synaptonemal complex in Atm mutant spermatocytes, which form synapses but show persistent trimethylation of histone H3 lysine 4. In order to further address a role of epigenetic modifications in DIDO3 localization, we made a mutant of the Dido gene that produces a truncated DIDO3 protein. This truncated protein, which lacks the histone-binding domain, is incorporated in the synaptonemal complex irrespective of histone trimethylation status. DIDO3 protein truncation in Dido mutant mice causes mild meiotic defects, visible as gaps in the synaptonemal complex, but allows for normal meiotic progression. Our results indicate that histone H3 lysine 4 demethylation modulates DIDO3 localization in meiosis and suggest epigenetic regulation of the synaptonemal complex.