Molecular programs guiding arealization of descending cortical pathways.

Layer 5 extratelencephalic (ET) neurons are present across neocortical areas and send axons to multiple subcortical targets1-6. Two cardinal subtypes exist7,8: (1) Slco2a1-expressing neurons (ETdist), which predominate in the motor cortex and project distally to the pons, medulla and spinal cord; and (2) Nprs1- or Hpgd-expressing neurons (ETprox), which predominate in the visual cortex and project more proximally to the pons and thalamus. An understanding of how area-specific ETdist and ETprox emerge during development is important because they are critical for fine motor skills and are susceptible to spinal cord injury and amyotrophic lateral sclerosis9-12. Here, using cross-areal mapping of axonal projections in the mouse neocortex, we identify the subtype-specific developmental dynamics of ET neurons. Whereas subsets of ETprox emerge by pruning of ETdist axons, others emerge de novo. We outline corresponding subtype-specific developmental transcriptional programs using single-nucleus sequencing. Leveraging these findings, we use postnatal in vivo knockdown of subtype-specific transcription factors to reprogram ET neuron connectivity towards more proximal targets. Together, these results show the functional transcriptional programs driving ET neuron diversity and uncover cell subtype-specific gene regulatory networks that can be manipulated to direct target specificity in motor corticofugal pathways.

Extracellular vesicle-mediated trafficking of molecular cues during human brain development.

Cellular crosstalk is an essential process influenced by numerous factors, including secreted vesicles that transfer nucleic acids, lipids, and proteins between cells. Extracellular vesicles (EVs) have been the center of many studies focusing on neurodegenerative disorders, but whether EVs display cell-type-specific features for cellular crosstalk during neurodevelopment is unknown. Here, using human-induced pluripotent stem cell-derived cerebral organoids, neural progenitors, neurons, and astrocytes, we identify heterogeneity in EV protein content and dynamics in a cell-type-specific and time-dependent manner. Our results support the trafficking of key molecules via EVs in neurodevelopment, such as the transcription factor YAP1, and their localization to differing cell compartments depending on the EV recipient cell type. This study sheds new light on the biology of EVs during human brain development.

Non-cell-autonomous regulation of interneuron specification mediated by extracellular vesicles.

Disruption in neurogenesis and neuronal migration can influence the assembly of cortical circuits, affecting the excitatory-inhibitory balance and resulting in neurodevelopmental and neuropsychiatric disorders. Using ventral cerebral organoids and dorsoventral cerebral assembloids with mutations in the extracellular matrix gene LGALS3BP, we show that extracellular vesicles released into the extracellular environment regulate the molecular differentiation of neurons, resulting in alterations in migratory dynamics. To investigate how extracellular vesicles affect neuronal specification and migration dynamics, we collected extracellular vesicles from ventral cerebral organoids carrying a mutation in LGALS3BP, previously identified in individuals with cortical malformations and neuropsychiatric disorders. These results revealed differences in protein composition and changes in dorsoventral patterning. Proteins associated with cell fate decision, neuronal migration, and extracellular matrix composition were altered in mutant extracellular vesicles. Moreover, we show that treatment with extracellular vesicles changes the transcriptomic profile in neural progenitor cells. Our results indicate that neuronal molecular differentiation can be influenced by extracellular vesicles.

Heterogeneous fates of simultaneously-born neurons in the cortical ventricular zone.

Neocortical excitatory neurons belong to diverse cell types, which can be distinguished by their dates of birth, laminar location, connectivity, and molecular identities. During embryogenesis, apical progenitors (APs) located in the ventricular zone first give birth to deep-layer neurons, and next to superficial-layer neurons. While the overall sequential construction of neocortical layers is well-established, whether APs produce multiple neuron types at single time points of corticogenesis is unknown. To address this question, here we used FlashTag to fate-map simultaneously-born (i.e. isochronic) cohorts of AP daughter neurons at successive stages of corticogenesis. We reveal that early in corticogenesis, isochronic neurons differentiate into heterogeneous laminar, hodological and molecular cell types. Later on, instead, simultaneously-born neurons have more homogeneous fates. Using single-cell gene expression analyses, we identify an early postmitotic surge in the molecular heterogeneity of nascent neurons during which some early-born neurons initiate and partially execute late-born neuron transcriptional programs. Together, these findings suggest that as corticogenesis unfolds, mechanisms allowing increased homogeneity in neuronal output are progressively implemented, resulting in progressively more predictable neuronal identities.

Author Correction: Temporal plasticity of apical progenitors in the developing mouse neocortex.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Temporal plasticity of apical progenitors in the developing mouse neocortex.

The diverse subtypes of excitatory neurons that populate the neocortex are born from apical progenitors located in the ventricular zone. During corticogenesis, apical progenitors sequentially generate deep-layer neurons followed by superficial-layer neurons directly or via the generation of intermediate progenitors. Whether neurogenic fate progression necessarily implies fate restriction in single progenitor types is unknown. Here we specifically isolated apical progenitors and intermediate progenitors, and fate-mapped their respective neuronal progeny following heterochronic transplantation into younger embryos. We find that apical progenitors are temporally plastic and can re-enter past molecular, electrophysiological and neurogenic states when exposed to an earlier-stage environment by sensing dynamic changes in extracellular Wnt. By contrast, intermediate progenitors are committed progenitors that lack such retrograde fate plasticity. These findings identify a diversity in the temporal plasticity of neocortical progenitors, revealing that some subtypes of cells can be untethered from their normal temporal progression to re-enter past developmental states.

Progenitor Hyperpolarization Regulates the Sequential Generation of Neuronal Subtypes in the Developing Neocortex.

During corticogenesis, ventricular zone progenitors sequentially generate distinct subtypes of neurons, accounting for the diversity of neocortical cells and the circuits they form. While activity-dependent processes are critical for the differentiation and circuit assembly of postmitotic neurons, how bioelectrical processes affect nonexcitable cells, such as progenitors, remains largely unknown. Here, we reveal that, in the developing mouse neocortex, ventricular zone progenitors become more hyperpolarized as they generate successive subtypes of neurons. Experimental in vivo hyperpolarization shifted the transcriptional programs and division modes of these progenitors to a later developmental status, with precocious generation of intermediate progenitors and a forward shift in the laminar, molecular, morphological, and circuit features of their neuronal progeny. These effects occurred through inhibition of the Wnt-beta-catenin signaling pathway by hyperpolarization. Thus, during corticogenesis, bioelectric membrane properties are permissive for specific molecular pathways to coordinate the temporal progression of progenitor developmental programs and thus neocortical neuron diversity.

Both exo- and endo-nucleolytic activities of RNase J1 from Staphylococcus aureus are manganese dependent and active on triphosphorylated 5'-ends.

RNA decay and RNA maturation are important steps in the regulation of bacterial gene expression. RNase J, which is present in about half of bacterial species, has been shown to possess both endo- and 5' to 3' exo-ribonuclease activities. The exonucleolytic activity is clearly involved in the degradation of mRNA and in the maturation of at least the 5' end of 16S rRNA in the 2 Firmicutes Staphylococcus aureus and Bacillus subtilis. The endoribonuclease activity of RNase J from several species has been shown to be weak in vitro and 3-D structural data of different RNase J orthologs have not provided a clear explanation for the molecular basis of this activity. Here, we show that S. aureus RNase J1 is a manganese dependent homodimeric enzyme with strong 5' to 3' exo-ribonuclease as well as endo-ribonuclease activity. In addition, we demonstrated that SauJ1 can efficiently degrade 5' triphosphorylated RNA. Our results highlight RNase J1 as an important player in RNA turnover in S. aureus.

Caracterización de la consulta institucional en psicosis y autismo infantil en la ciudad de Buenos Aires. Estudio de caso / Characterization of institutional consultation in infantile psychosis and autism in the city of Buenos Aires case study

El presente trabajo pretende exponer y reflexionar acerca de las dificultades en el acceso a los servicios de salud de niños/as con trastornos psicopatológicos graves.Se trata de un estudio epidemiológico y descriptivo, acerca de las respuestas institucionales del sector público frente al padecimiento estos niños/as diagnosticados con autismo y psicosis infantil. Se enmarca en una perspectiva de investigación en Sistemas y Servicios de Salud cuyo enfoque es interdisciplinario y propone avanzar en metodologías de evaluación sobre organización y utilización de Servicios de salud mental en la infancia.El análisis se centra en el Hospital de Día Infantil perteneciente al Centro de Salud Mental N°1, el cual constituye uno de los dos únicos centros de referencia y derivación del sector público especializados en la atención de niños/as psicóticos y autistas, pertenecientes al gobierno de la Ciudad de Buenos Aires. En el trabajo se desarrolla una caracterización y análisis de las consultas al servicio, en el período comprendido entre los años 1995/1999. También evalúa las modificaciones en el perfil de las consultas, la situación socioeconómica de las familias que concurren al Hospital de Día y profundiza acerca de los principales obstáculos y dificultades en el acceso a los servicios de salud mental infantil.