Normal neonatal TREC and KREC levels in early onset juvenile idiopathic arthritis.

OBJECTIVE: Dysregulated central tolerance predisposes to autoimmune diseases. Reduced thymic output as well as compromised central B cell tolerance checkpoints have been proposed in the pathogenesis of juvenile idiopathic arthritis (JIA). The aim of this study was to investigate neonatal levels of T-cell receptor excision circles (TRECs) and kappa-deleting element excision circles (KRECs), as markers of T- and B-cell output at birth, in patients with early onset JIA. METHODS: TRECs and KRECs were quantitated by multiplex qPCR from dried blood spots (DBS), collected 2-5 days after birth, in 156 children with early onset JIA and in 312 matched controls. RESULTS: When analysed from neonatal dried blood spots, the median TREC level was 78 (IQR 55-113) in JIA cases and 88 (IQR 57-117) copies/well in controls. The median KREC level was 51 (IQR 35-69) and 53 (IQR 35-74) copies/well, in JIA cases and controls, respectively. Stratification by sex and age at disease onset did not reveal any difference in the levels of TRECs and KRECs. CONCLUSION: T- and B-cell output at birth, as measured by TREC and KREC levels in neonatal dried blood spots, does not differ in children with early onset JIA compared to controls.

First Year of TREC-Based National SCID Screening in Sweden.

Screening for severe combined immunodeficiency (SCID) was introduced into the Swedish newborn screening program in August 2019 and here we report the results of the first year. T cell receptor excision circles (TRECs), kappa-deleting element excision circles (KRECs), and actin beta (ACTB) levels were quantitated by multiplex qPCR from dried blood spots (DBS) of 115,786 newborns and children up to two years of age, as an approximation of the number of recently formed T and B cells and sample quality, respectively. Based on low TREC levels, 73 children were referred for clinical assessment which led to the diagnosis of T cell lymphopenia in 21 children. Of these, three were diagnosed with SCID. The screening performance for SCID as the outcome was sensitivity 100%, specificity 99.94%, positive predictive value (PPV) 4.11%, and negative predictive value (NPV) 100%. For the outcome T cell lymphopenia, PPV was 28.77%, and specificity was 99.95%. Based on the first year of screening, the incidence of SCID in the Swedish population was estimated to be 1:38,500 newborns.

ALK4 coordinates extracellular and intrinsic signals to regulate development of cortical somatostatin interneurons.

Although the role of transcription factors in fate specification of cortical interneurons is well established, how these interact with extracellular signals to regulate interneuron development is poorly understood. Here we show that the activin receptor ALK4 is a key regulator of the specification of somatostatin interneurons. Mice lacking ALK4 in GABAergic neurons of the medial ganglionic eminence (MGE) showed marked deficits in distinct subpopulations of somatostatin interneurons from early postnatal stages of cortical development. Specific losses were observed among distinct subtypes of somatostatin+/Reelin+ double-positive cells, including Hpse+ layer IV cells targeting parvalbumin+ interneurons, leading to quantitative alterations in the inhibitory circuitry of this layer. Activin-mediated ALK4 signaling in MGE cells induced interaction of Smad2 with SATB1, a transcription factor critical for somatostatin interneuron development, and promoted SATB1 nuclear translocation and repositioning within the somatostatin gene promoter. These results indicate that intrinsic transcriptional programs interact with extracellular signals present in the environment of MGE cells to regulate cortical interneuron specification.

Electrotonic Coupling in the Pituitary Supports the Hypothalamic-Pituitary-Gonadal Axis in a Sex Specific Manner.

Gap junctions are present in many cell types throughout the animal kingdom and allow fast intercellular electrical and chemical communication between neighboring cells. Connexin-36 (Cx36), the major neuronal gap junction protein, synchronizes cellular activity in the brain, but also in other organs. Here we identify a sex-specific role for Cx36 within the hypothalamic-pituitary-gonadal (HPG) axis at the level of the anterior pituitary gland (AP). We show that Cx36 is expressed in gonadotropes of the AP sustaining their synchronous activity. Cx36 ablation affects the entire downstream HPG axis in females, but not in males. We demonstrate that Cx36-mediated coupling between gonadotropes in the AP supports gonadotropin-releasing hormone-induced secretion of luteinizing hormone. Furthermore, we provide evidence for negative feedback regulation of Cx36 expression in the AP by estradiol. We thus, conclude that hormonally-controlled plasticity of gap junction communication at the level of the AP constitutes an additional mechanism affecting female reproduction.

GluN2B-containing NMDA receptors promote glutamate synapse development in hippocampal interneurons.

In postnatal development, GluN2B-containing NMDARs are critical for the functional maturation of glutamatergic synapses. GluN2B-containing NMDARs prevail until the second postnatal week when GluN2A subunits are progressively added, conferring mature properties to NMDARs. In cortical principal neurons, deletion of GluN2B results in an increase in functional AMPAR synapses, suggesting that GluN2B-containing NMDARs set a brake on glutamate synapse maturation. The function of GluN2B in the maturation of glutamatergic inputs to cortical interneurons is not known. To examine the function of GluN2B in interneurons, we generated mutant mice with conditional deletion of GluN2B in interneurons (GluN2B(ΔGAD67)). In GluN2B(ΔGAD67) mice interneurons distributed normally in cortical brain regions. After the second postnatal week, GluN2B(ΔGAD67) mice developed hippocampal seizures and died shortly thereafter. Before the onset of seizures, GluN2B-deficient hippocampal interneurons received fewer glutamatergic synaptic inputs than littermate controls, indicating that GluN2B-containing NMDARs positively regulate the maturation of glutamatergic input synapses in interneurons. These findings suggest that GluN2B-containing NMDARs keep the circuit activity under control by promoting the maturation of excitatory synapses in interneurons.

Neuroendocrine control of female reproductive function by the activin receptor ALK7.

Activins are critical components of the signaling network that controls female reproduction. However, their roles in hypothalamus, and the specific functions of their different receptors, have not been elucidated. Here, we investigated the expression and function of the activin receptor ALK7 in the female reproductive axis using Alk7-knockout mice. ALK7 was found in subsets of SF1-expressing granulosa cells in the ovary, FSH gonadotrophs in the pituitary, and NPY-expressing neurons in the arcuate nucleus of the hypothalamus. Alk7-knockout females showed delayed onset of puberty and abnormal estrous cyclicity, had abnormal diestrous levels of FSH and LH in serum, and their ovaries showed premature depletion of follicles, oocyte degeneration, and impaired responses to exogenous gonadotropins. In the arcuate nucleus, mutant mice showed reduced expression of Npy mRNA and lower numbers of Npy-expressing neurons than wild-type controls. Alk7 knockouts showed a selective loss of arcuate NPY/AgRP innervation in the medial preoptic area, a key central regulator of reproduction. These results indicate that ALK7 is an important regulator of female reproductive function and reveal a new role for activin signaling in the control of hypothalamic gene expression and wiring. Alk7 gene variants may contribute to female reproductive disorders in humans, such as polycystic ovary syndrome.

Contribution of hippocampal and extra-hippocampal NR2B-containing NMDA receptors to performance on spatial learning tasks.

Controversy revolves around the differential contribution of NR2A- and NR2B-containing NMDA receptors, which coexist in principal forebrain neurons, to synaptic plasticity and learning in the adult brain. Here, we report genetically modified mice in which the NR2B subunit is selectively ablated in principal neurons of the entire postnatal forebrain or only the hippocampus. NR2B ablation resulted in smaller NMDA receptor-mediated EPSCs with accelerated decay kinetics, as recorded in CA1 pyramidal cells. CA3-to-CA1 field LTP remained largely unaltered, although a pairing protocol revealed decreased NMDA receptor-mediated charge transfer and reduced cellular LTP. Mice lacking NR2B in the forebrain were impaired on a range of memory tasks, presenting both spatial and nonspatial phenotypes. In contrast, hippocampus-specific NR2B ablation spared hippocampus-dependent, hidden-platform water maze performance but induced a selective, short-term, spatial working memory deficit for recently visited places. Thus, both hippocampal and extra-hippocampal NR2B containing NMDA receptors critically contribute to spatial performance.

A mouse translocation associated with Caspr5-2 disruption and perinatal lethality.

We have previously described the paralogous mouse genes Caspr5-1, -2, and -3 of the neurexin gene family. Here we present the cytogenetic and molecular mapping of a null mutation of Caspr5-2 which was caused by reciprocal translocation between chromosomes 1 and 8 with breakpoints at bands 1E2.1 and 8B2.1, respectively. The translocation disrupts Caspr5-2 between exons 1 and 2 and causes stillbirth or early postnatal lethality of homozygous carriers. Because no other candidate genes were found, the disruption of Caspr5-2 is most likely the cause of lethality. Only rarely do homozygotes survive the critical stage, reach fertility, and are then apparently normal. They may be rescued by one of the two other Caspr5 paralogs. Caspr5-2 is expressed in spinal cord and brain tissues. Despite giving special attention to regions where in wild-type fetuses maximum expression was found, no malformation that might have caused death could be detected in fetal homozygous carriers of the translocation. We, therefore, suspect that Caspr5-2 disruption leads to dysfunction at the cellular level rather than at the level of organ development.