O colecionismo etnográfico no Brasil (1955-1975): entrevista com René Fuerst

Heritage of Indigenous People

Genetics and physiology of defective lysogeny in K12 (λ): Studies of early mutants

The properties of a number of strains of K12 (λ) which are defective in their ability to form lambda DNA after induction have been examined by genetic, physiological, and biochemical tests. The strains fall into four classes, and include mutants in cistrons N, O, and P, previously identified by Campbell (1961), and a fourth new class, called x, in a region between CI and CII. Mutants in each of the classes can be distinguished genetically, by their relative ability to form the λ-exonuclease, and by their tendency to show curing of their prophage after induction. Mutants in the P and O cistrons form normal levels of λ-exonuclease, whereas mutants in the N cistron form very low levels, and mutants in the x region, relatively high levels of this enzyme. Curing is very efficient for mutants in the x region, less efficient for mutants in the O and P cistrons, and is seldom observed with mutants in the N cistron. These patterns of curing are reflected in the curves for UV survival of the strains carrying defective mutations in the various cistrons. The significance of these findings in respect to the early events in phage development are discussed. © 1966.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

DSCAM gene triplication causes excessive GABAergic synapses in the neocortex in Down syndrome mouse models

Down syndrome (DS) is caused by the trisomy of human chromosome 21 (HSA21). A major challenge in DS research is to identify the HSA21 genes that cause specific symptoms. Down syndrome cell adhesion molecule (DSCAM) is encoded by a HSA21 gene. Previous studies have shown that the protein level of the Drosophila homolog of DSCAM determines the size of presynaptic terminals. However, whether the triplication of DSCAM contributes to presynaptic development in DS remains unknown. Here, we show that DSCAM levels regulate GABAergic synapses formed on neocortical pyramidal neurons (PyNs). In the Ts65Dn mouse model for DS, where DSCAM is overexpressed due to DSCAM triplication, GABAergic innervation of PyNs by basket and chandelier interneurons is increased. Genetic normalization of DSCAM expression rescues the excessive GABAergic innervations and the increased inhibition of PyNs. Conversely, loss of DSCAM impairs GABAergic synapse development and function. These findings demonstrate excessive GABAergic innervation and synaptic transmission in the neocortex of DS mouse models and identify DSCAM overexpression as the cause. They also implicate dysregulated DSCAM levels as a potential pathogenic driver in related neurological disorders. Developmental brain disorders are a hallmark of Down syndrome, but what cellular and molecular mechanisms underlie these disorders? This study shows that the excessive number of inhibitory synapses in the neocortex of Down syndrome mouse models is caused by increased levels of Down Syndrome Cell Adhesion Molecule (DSCAM)

Excitability, firing rate, and sEPSCs of ChCs (related to Fig 2).

Quantification of electrophysiology parameters of ChCs in the ACC in euploid (gray), Ts65Dn (light blue), and Ts65Dn:DSCAM+/+/− (pink) brain slices. Kruskal–Wallis test with post hoc Mann–Whitney tests for two-group comparisons, except for (G). *: p p > 0.05). (A-F) Quantifications of membrane potential (mV) (A), threshold (mV) (B), SAP amplitude (mV) (C), SAP half-width (ms) (D), the depolarization velocity of SAP (dv/dt) (E), and repolarization velocity of SAP (dv/dt) (F). Cell numbers: 13 for euploid, 9 for Ts65Dn, and 8 Ts65Dn:DSCAM+/+/−. (G) Curves showing the relationship between the average firing frequencies of evoked AP (Hz) and the currents (pA) in ChCs. Two-way ANOVA, Tukey’s multiple comparisons test. Euploid vs. Ts65Dn: p DSCAM+/+/−: p > 0.05. (H) Rheobase (pA) from ChCs in (G). Cell numbers: 13 for euploid, 9 for Ts65Dn, and 9 Ts65Dn:DSCAM+/+/−. (I, J) Quantification of sEPSC frequency (I) and amplitude (J). For each mouse, 2–4 PyNs were recorded. Cell numbers: 12 for euploid, 7 for Ts65Dn, and 7 Ts65Dn:DSCAM+/+/−. The data underlying this Figure can be found in https://doi.org/10.5281/zenodo.7714234. ACC, anterior cingulate cortex; ChC, chandelier cell; DSCAM, Down syndrome cell adhesion molecule; SAP, single action potential; sEPSC, spontaneous excitatory postsynaptic current. (TIF)</p

DSCAM regulates ChC cartridge length and synaptogenesis in a dosage-dependent manner (related to Figs 3 and 5).

(A) Western blots showing DSCAM levels in the neocortex. The mouse neocortex was taken immediately after perfusion. (B-E) The correlation analyses between DSCAM expression level and ChC cartridge length (B), bouton number (C), bouton size (D), or interbouton distance (E). In (B), the DSCAM level of a mouse is plotted against the mean of the total cartridge length in the volume specified in S1 Fig in this mouse. The average cartridge length is calculated as the average value of 4–6 ChCs sampled in each mouse. A total of 4 euploid (gray dots), 5 Ts65Dn (cyan dots), and 4 Ts65Dn:DSCAM+/+/− (red dots) mice were analyzed. R2 and p are calculated for linear regression. The data underlying this Figure can be found in https://doi.org/10.5281/zenodo.7714234. ChC, chandelier cell; DSCAM, Down syndrome cell adhesion molecule. (TIF)</p

Genetic normalization of DSCAM levels rescues the number of GABAergic boutons formed on PyN somas in Ts65Dn mice.

(A) DSCAM overexpression is normalized to the euploid level in Ts65Dn mice by introducing the DSCAM2j loss-of-function allele. Euploid, Ts65Dn, and Ts65Dn:DSCAM+/+/− mice were obtained by crossing female Ts65Dn mice with the male DSCAM2j. Shown are representative western blots (top) and quantifications (bottom) of neocortical samples from each indicated genotype. Each dot in the bar chart represents the sample from 1 mouse. (B) A schematic of the procedure that produced the mice for the experiments. (C) Representative images of perisomatic GABAergic boutons innervating PyNs in layer II/III of the ACC of euploid (wild-type), Ts65Dn, and Ts65Dn:DSCAM+/+/− (i.e., global normalization of DSCAM dosage). The right panel in each genotype group is the magnified view of the regions boxed by dotted lines in the left panel. The soma and proximal dendrites of PyNs were labeled by GRASP1. Yellow arrowheads point to GABAergic boutons as indicated by Bassoon+ puncta that overlapped with VGAT+ puncta. (D) Representative images of perisomatic GABAergic boutons innervating PyNs in layer II/III of the ACC of euploid:Lhx6-Cre+/−; (2) Ts65Dn:Lhx6-Cre+/−; and (3) Ts65Dn:Lhx6-Cre+/−/DSCAMflox (i.e., GABAergic-neuron normalization of DSCAM dosage). (E, F) Quantification of the number of perisomatic GABAergic boutons per PyN in global (E) and GABAergic-neuron (F) normalization of DSCAM dosage experiments. For each mouse, 5–7 PyNs were analyzed; each data point in the chart represents the mean in 1 mouse. Unless specified, mean ± SEM is shown in the figures, and the statistical tests are one-way ANOVA for multi-group comparisons and post hoc Student t tests for pair-wise comparisons. **: p p p https://doi.org/10.5281/zenodo.7714234. ACC, anterior cingulate cortex; DSCAM, Down syndrome cell adhesion molecule; PyN, pyramidal neuron.</p

DSCAM expression levels in the mutant mice used in this study (related to Figs 4 and 5).

Representative western blots and quantifications of protein samples collected from the somatosensory cortex of DSCAM+/+ (+/+), DSCAM2j/+ (+/−), and DSCAM2j/2j (−/−) mice. DSCAM protein was not detected in DSCAM−/− by western blotting (A). The level of DSCAM protein in DSCAM+/− was about 81% of that in DSCAM+/+ (B). Student t test. *: p p https://doi.org/10.5281/zenodo.7714234. DSCAM, Down syndrome cell adhesion molecule. (TIF)</p

The original, uncropped, and minimally adjusted images supporting all blot and gel results reported in the figures and supporting information files (related to Figs 1, S8, and S10).

The original, uncropped, and minimally adjusted images supporting all blot and gel results reported in the figures and supporting information files (related to Figs 1, S8, and S10).</p