CEP120-mediated KIAA0753 recruitment onto centrioles is required for timely neuronal differentiation and germinal zone exit in the developing cerebellum

Joubert syndrome (JS) is a recessive ciliopathy in which all affected individuals have congenital cerebellar vermis hypoplasia. Here, we report that CEP120, a JS-associated protein involved in centriole biogenesis and cilia assembly, regulates timely neuronal differentiation and the departure of granule neuron progenitors (GNPs) from their germinal zone during cerebellar development. Our results show that depletion of Cep120 perturbs GNP cell cycle progression, resulting in a delay of cell cycle exit in vivo. To dissect the potential mechanism, we investigated the association between CEP120 interactome and the JS database and identified KIAA0753 (a JS-associated protein) as a CEP120-interacting protein. Surprisingly, we found that CEP120 recruits KIAA0753 to centrioles, and that loss of this interaction induces accumulation of GNPs in the germinal zone and impairs neuronal differentiation. Importantly, the replenishment of wild-type CEP120 rescues the above defects, whereas expression of JS-associated CEP120 mutants, which hinder KIAA0753 recruitment, does not. Together, our data reveal a close interplay between CEP120 and KIAA0753 for the germinal zone exit and timely neuronal differentiation of GNPs during cerebellar development, and mutations in CEP120 and KIAA0753 may participate in the heterotopia and cerebellar hypoplasia observed in JS patients.

Fine structure of spermatogenesis in the spider crab Lissa chiragra (Fabricius, 1775) (Eubrachyura, Epialtidae)

This article uses the male spider crab Lissa chiragra, collected from Ras el Tin beach on the Mediterranean Sea at Alexandria, Egypt, between January and December 2017, as a model for a descriptive study of the functional morphology of the different structures of spermatogenesis with the aid of the transmission electron microscope. This study divides the seminiferous tubule into three zones, i.e., the germinal, transformation, and evacuation zone. The transformation or maturation zone occupies the central area. The evacuation zone lies at a pole opposite to the germinal zone. The anterior vas deferens is a tube where the formation of the spermatophore occurs by means of secretions from the epithelium. The ejaculatory duct is located between the muscles of the coxae of the fifth walking legs. This study concluded that the complex acrosome vesicle is formed during spermiogenesis and the cytoplasm includes the membrane system, constituted by the endoplasmic reticulum, Golgi apparatus, and vesicles associated with microtubules, and a few mitochondria. The Golgi apparatus is developed and is organized progressively to produce various vesicles. The cytoplasm forms a ring at the base of the nuclear extensions. The merger of the plasma and nuclear membranes, results in a pentalaminar membranous structure in some regions of the cell surface.

Perinatal Inflammation Disturbs Secondary Germinal Zone Neurogenesis and Gliogenesis Producing Deficits in Sociability

Epidemiologic studies have demonstrated that infections during pregnancy increase the risk of offspring developing Schizophrenia, Autism, Depression and Bipolar Disorder and have implicated interleukin-6 (IL-6) as a causal agent. However, other cytokines have been associated with psychiatric disorders; therefore, it remains to be established whether elevating IL-6 is sufficient to alter the trajectory of neural development. Furthermore, most rodent studies have manipulated the maternal immune system at mid-gestation, which affects the stem cells and progenitors in both the primary and secondary germinal matrices. Therefore, a question that remains to be addressed is whether elevating IL-6 when the secondary germinal matrices are most active will affect brain development. Here, we have increased IL-6 from postnatal days 3-6, when the secondary germinal matrices are rapidly expanding. Using Nestin-CreERT2 fate mapping we show that this transient increase in IL-6 decreased neurogenesis in the dentate gyrus of the dorsal hippocampus, reduced astrogliogenesis in the prefrontal cortex and amygdala and decreased oligodendrogenesis in the body and splenium of the corpus callosum all by ~50%. Moreover, the IL-6 treatment elicited behavioral changes classically associated with neurodevelopmental disorders. As adults, IL-6 injected male mice lost social preference in the social approach test, spent ~30% less time socially engaging with sexually receptive females and produced ~50% fewer ultrasonic vocalizations during mating. They also engaged ~50% more time in self-grooming behavior and had an increase in inhibitory avoidance. Altogether, these data provide new insights into the biological mechanisms linking perinatal immune activation to complex neurodevelopmental brain disorders.

MiR-137 and miR-122, two outer subventricular zone-enriched non-coding RNAs, regulate basal progenitor expansion and neuronal differentiation

Cortical expansion in the primate brain relies on the presence and the spatial enlargement of multiple germinal zones during development and on a prolonged developmental period. In contrast to other mammals, which have two cortical germinal zones, the ventricular zone (VZ) and subventricular zone (SVZ), gyrencephalic species display an additional germinal zone, the outer subventricular zone (OSVZ), which role is to increase the number and types of neurons generated during corticogenesis. How the OSVZ emerged during evolution is poorly understood but recent studies suggest a role for non-coding RNAs, which allow tight regulations of transcriptional programs in time and space during development (Dehay et al. 2015; Arcila et al., 2014). Here, using in vivo functional genetics, single-cell RNA sequencing, live imaging and electrophysiology to assess progenitor and neuronal properties in mice, we identify two ferret and human OSVZ-enriched microRNAs (miR), miR-137 and miR-122, which regulate key cellular features associated with cortical expansion. MiR-137 promotes basal progenitor self-replication and superficial layer neuron fate, while miR-122 slows down neuronal differentiation pace. Together, these findings support a cell-type specific role for miR-mediated transcriptional regulation in cortical expansion.

LONG TERM RESULTS OF REVERSE TRANSOSAL SUTURE OF FINGER FLEXOR TENDON TO DISTAL PHALANGE

Aim: To analyze results of proposed reverse transosal suture. Materials: 264 cases (187 patients; 143 men, 44 women, age between 5 to 75 y. o.) of tendon fixation to distal phalanx by proposed technique was accepted in our research, after two stages flexor tendon grafting, in 2008—2019. On 2nd day after surgery - early full amplitude movement rehabilitation protocol (modification of Kleinart technique) was applied. Results: In an interim analysis of 109 patients treatment results, we noted complications associated with a transossal tendon suture to distal phalanx in 7.5 % (8/159) of cases: infectious complication — 1 case, serious nail growth disorders — 1, slight deformation of the nail plate — 5 cases, periodic pain in distant period — 1 case. To avoid complications associated with nail plate disorders, suture technique was modified by displacing the transcutaneous canal to the side of the nail germinal zone without incision on the back of the finger. No deformation of the nail plate was observed after changing of suture technique. Conclusions: flexor digitorum profundus tendon fixation technique minimizes trauma to surrounding tissues. Strong internal fixation of the tendon gives the possibility of early movements. Intermediate material analysis made it possible to change the suture technique to effectively eliminate the most common complications.

Siah2 integrates mitogenic and extracellular matrix signals linking neuronal progenitor ciliogenesis with germinal zone occupancy

Evidence is lacking as to how developing neurons integrate mitogenic signals with microenvironment cues to control proliferation and differentiation. We determine that the Siah2 E3 ubiquitin ligase functions in a coincidence detection circuit linking responses to the Shh mitogen and the extracellular matrix to control cerebellar granule neurons (CGN) GZ occupancy. We show that Shh signaling maintains Siah2 expression in CGN progenitors (GNPs) in a Ras/Mapk-dependent manner. Siah2 supports ciliogenesis in a feed-forward fashion by restraining cilium disassembly. Efforts to identify sources of the Ras/Mapk signaling led us to discover that GNPs respond to laminin, but not vitronectin, in the GZ microenvironment via integrin β1 receptors, which engages the Ras/Mapk cascade with Shh, and that this niche interaction is essential for promoting GNP ciliogenesis. As GNPs leave the GZ, differentiation is driven by changing extracellular cues that diminish Siah2-activity leading to primary cilia shortening and attenuation of the mitogenic response.

Proneural genes define ground state rules to regulate neurogenic patterning and cortical folding

SUMMARYTransition from smooth, lissencephalic brains to highly-folded, gyrencephalic structures is associated with neuronal expansion and breaks in neurogenic symmetry. Here we show that Neurog2 and Ascl1 proneural genes regulate cortical progenitor cell differentiation through cross-repressive interactions to sustain neurogenic continuity in a lissencephalic rodent brain. Using in vivo lineage tracing, we found that Neurog2 and Ascl1 expression defines a lineage continuum of four progenitor pools, with ‘double+ progenitors’ displaying several unique features (least lineage-restricted, complex gene regulatory network, G2 pausing). Strikingly, selective killing of double+ progenitors using split-Cre;Rosa-DTA transgenics breaks neurogenic symmetry by locally disrupting Notch signaling, leading to cortical folding. Finally, consistent with NEUROG2 and ASCL1 driving discontinuous neurogenesis and folding in gyrencephalic species, their transcripts are modular in folded macaque cortices and pseudo-folded human cerebral organoids. Neurog2/Ascl1 double+ progenitors are thus Notch-ligand expressing ‘niche’ cells that control neurogenic periodicity to determine cortical gyrification.HIGHLIGHTSNeurog2 and Ascl1 expression defines four distinct transitional progenitor statesDouble+ NPCs are transcriptionally complex and mark a lineage branch pointDouble+ NPCs control neurogenic patterning and cortical folding via Notch signalingNeurog2 and Ascl1 expression is modular in folded and not lissencephalic corticeseTOC BLURBEmergence of a gyrencephalic cortex is associated with a break in neurogenic continuity across the cortical germinal zone. Han et al. identify a pool of unbiased neural progenitors at a lineage bifurcation point that co-express Neurog2 and Ascl1 and produce Notch ligands to control neurogenic periodicity and cortical folding.

A subpopulation of astrocyte progenitors defined by Sonic hedgehog signaling

ABSTRACTThe molecular signaling pathway, Sonic hedgehog (Shh), is critical for the proper development of the central nervous system. The requirement for Shh signaling in neuronal and oligodendrocyte development in the developing embryo are well established. Here, we show that Shh signaling also operates in a subpopulation of progenitor cells that generate cortical astrocytes. In the neonatal brain, cells expressing the Shh target gene, Gli1, are found in the subventricular zone (SVZ), a germinal zone harboring astrocyte progenitor cells. Using a genetic inducible fate mapping strategy, we show that these cells give rise to half of the cortical astrocyte population, suggesting that the cortex harbors astrocytes from different lineages. Shh activity in SVZ progenitor cells is transient but recurs in a subpopulation of mature astrocytes localized in layers IV and V in a manner independent of their lineage. These data identify a novel role for Shh signaling in cortical astrocyte development and support a growing body of evidence pointing to astrocyte heterogeneity.