Myelin is a defining feature of the vertebrate nervous system. Variability in the thickness of the myelin envelope is a structural feature affecting the conduction of neuronal signals. Conversely, the distribution of myelinated tracts along the length of axons has been assumed to be uniform. Here, we traced high-throughput electron microscopy (EM) reconstructions of single axons of pyramidal neurons in the mouse neocortex and built high-resolution maps of myelination. We find that individual neurons have distinct longitudinal distribution of myelin. Neurons in the superficial layers displayed the most diversified profiles, including a new pattern where myelinated segments are interspersed with long, unmyelinated tracts. Our data indicate that the profile of longitudinal distribution of myelin is an integral feature of neuronal identity and may have evolved as a strategy to modulate long-distance communication in the neocortex.

SUMMARY L3mbtl2 has been implicated in transcriptional repression and chromatin compaction but its biological function has not been defined. Here we show that disruption of L3mbtl2 results in embryonic lethality with failure of gastrulation. This correlates with compromised proliferation and abnormal differentiation of L3mbtl2−/− embryonic stem (ES) cells. L3mbtl2 regulates genes by recruiting a Polycomb Repressive Complex1 (PRC1)-related complex, resembling the previously described E2F6-complex, and including G9A, Hdac1, and Ring1b. Presence of L3mbtl2 at target genes is associated with H3K9-dimethylation, low histone-acetylation, and H2AK119-ubiquitination, but the latter is neither dependent on L3mbtl2 nor sufficient for repression. Genome wide studies revealed that the L3mbtl2-dependent complex predominantly regulates genes not bound by canonical PRC1 and PRC2. However, some developmental regulators are repressed by the combined activity of all three complexes. Together, we have uncovered a highly selective, essential role for an atypical PRC1-family complex in ES cells and early development.

Highlights d A searchable database of eQTL from macula and peripheral retina and RPE/choroid d Single-cell expression from human retina and RPE with cell subtype resolution d Integrative analysis of bulk and single-cell transcriptomics in the human eye d Co-localization of GWAS and eQTL identified putative causal genes for AMD

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SummaryThe scarcity of primordial germ cells (PGCs) in the developing mammalian embryo hampers robust biochemical analysis of the processes that underlie early germ cell formation. Here, we demonstrate that DAZL, a germ cell-specific RNA binding protein, is a robust PGC marker during in vitro germ cell development. Using Dazl-GFP reporter ESCs, we demonstrate that DAZL plays a central role in a large mRNA/protein interactive network that blocks the translation of core pluripotency factors, including Sox2 and Sall4, as well as of Suz12, a polycomb family member required for differentiation of pluripotent cells. Thus, DAZL limits both pluripotency and somatic differentiation in nascent PGCs. In addition, we observed that DAZL associates with mRNAs of key Caspases and similarly inhibits their translation. This elegant fail-safe mechanism ensures that, whereas loss of DAZL results in prolonged expression of pluripotency factors, teratoma formation is avoided due to the concomitant activation of the apoptotic cascade.