Drosophila Fezf functions as a transcriptional repressor to direct layer-specific synaptic connectivity in the fly visual system.

The layered compartmentalization of synaptic connections, a common feature of nervous systems, underlies proper connectivity between neurons and enables parallel processing of neural information. However, the stepwise development of layered neuronal connections is not well understood. The medulla neuropil of the Drosophila visual system, which comprises 10 discrete layers (M1 to M10), where neural computations underlying distinct visual features are processed, serves as a model system for understanding layered synaptic connectivity. The first step in establishing layer-specific connectivity in the outer medulla (M1 to M6) is the innervation by lamina (L) neurons of one of two broad, primordial domains that will subsequently expand and transform into discrete layers. We previously found that the transcription factor dFezf cell-autonomously directs L3 lamina neurons to their proper primordial broad domain before they form synapses within the developing M3 layer. Here, we show that dFezf controls L3 broad domain selection through temporally precise transcriptional repression of the transcription factor slp1 (sloppy paired 1). In wild-type L3 neurons, slp1 is transiently expressed at a low level during broad domain selection. When dFezf is deleted, slp1 expression is up-regulated, and ablation of slp1 fully rescues the defect of broad domain selection in dFezf-null L3 neurons. Although the early, transient expression of slp1 is expendable for broad domain selection, it is surprisingly necessary for the subsequent L3 innervation of the M3 layer. DFezf thus functions as a transcriptional repressor to coordinate the temporal dynamics of a transcriptional cascade that orchestrates sequential steps of layer-specific synapse formation.

Identification of FCN1 as a novel macrophage infiltration-associated biomarker for diagnosis of pediatric inflammatory bowel diseases.

BACKGROUND: The incidence of pediatric inflammatory bowel disease (PIBD) has been steadily increasing globally. Delayed diagnosis of PIBD increases the risk of complications and contributes to growth retardation. To improve long-term outcomes, there is a pressing need to identify novel markers for early diagnosis of PIBD. METHODS: The candidate biomarkers for PIBD were identified from the GSE117993 dataset by two machine learning algorithms, namely LASSO and mSVM-RFE, and externally validated in the GSE126124 dataset and our PIBD cohort. The role of ficolin-1 (FCN1) in PIBD and its association with macrophage infiltration was investigated using the CIBERSORT method and enrichment analysis of the single-cell dataset GSE121380, and further validated using immunoblotting, qRT-PCR, and immunostaining in colon biopsies from PIBD patients, a juvenile murine DSS-induced colitis model, and THP-1-derived macrophages. RESULTS: FCN1 showed great diagnostic performance for PIBD in an independent clinical cohort with the AUC of 0.986. FCN1 expression was upregulated in both colorectal biopsies and blood samples from PIBD patients. Functionally, FCN1 was associated with immune-related processes in the colonic mucosa of PIBD patients, and correlated with increased proinflammatory M1 macrophage infiltration. Furthermore, single-cell transcriptome analysis and immunostaining revealed that FCN1 was almost exclusively expressed in macrophages infiltrating the colonic mucosa of PIBD patients, and these FCN1+ macrophages were related to hyper-inflammation. Notably, proinflammatory M1 macrophages derived from THP-1 expressed high levels of FCN1 and IL-1ß, and FCN1 overexpression in THP-1-derived macrophages strongly promoted LPS-induced activation of the proinflammatory cytokine IL-1ß via the NLRP3-caspase-1 axis. CONCLUSIONS: FCN1 is a novel and promising diagnostic biomarker for PIBD. FCN1+ macrophages enriched in the colonic mucosa of PIBD exhibit proinflammatory phenotypes, and FCN1 promotes IL-1ß maturation in macrophages via the NLRP3-caspase-1 axis.

Assessing the Understanding of Helicobacter pylori Infection Among Chinese Pediatricians.

Background: Helicobacter pylori (Hp) is a global public health concern, particularly among children. While the "detection and treatment" approach gains ground in adult patients, paediatricians have divergent opinions regarding the current clinical protocols for diagnosing and treating Hp infection. Some argue for its potential impact on children's growth, emphasizing the need for adequate attention. Additionally, there are uncertainties regarding the appropriate screening tests for children who require Hp testing or have functional dyspepsia. Objective: This study aims to investigate pediatricians' current perspectives and understanding of Hp infection to provide valuable insights for Hp treatment. Methods: This study employs a cross-sectional research design. A questionnaire was designed using the "Questionnaire Star" platform and distributed online to physicians participating in the 12th Shanghai Pediatric Gastroenterology Forum in September 2020. The questionnaire covered topics such as physician professional information, the status of Hp diagnosis in hospitals, Hp knowledge, and knowledge of Hp treatment. Categorical data from each group were analyzed using chi-square tests to understand the diagnostic and treatment practices of pediatricians regarding Hp infection. Results: Among the 218 participating physicians who completed the questionnaire, 49.5% specialized in gastroenterology and practiced in hospitals equipped with Hp testing capabilities. Additionally, 85.8% practiced in hospitals with electronic gastroscopes. Notably, 94% considered Hp an infectious disease. Pediatric gastroenterology specialists, in particular, favored endoscopy for Hp detection compared to non-pediatric gastroenterologists. The investigation revealed variations in Hp detection understanding and consensus among the enrolled physicians. Challenges included determining the age for initiating Hp treatment in children and implementing family-based strategies. Conclusions: Further research is essential to inform the development of comprehensive detection and treatment strategies for Hp infection in children. Currently, the primary approach may involve individualized and standardized diagnosis and treatment.

Multi-omics reveals the mechanisms of DEHP driven pulmonary toxicity in ovalbumin-sensitized mice.

The plasticizer di- (2-ethylhexyl) phthalate (DEHP) is considered a risk factor for allergic diseases and has attracted public attention for its adverse effects on health. However, respiratory adverse effects after DEHP exposure in food allergies have rarely been reported. MiRNAs are considered to be key regulators in the complex interrelationships between the host and microbiome and may be a potential factor involved in DEHP-induced pulmonary toxicity. To investigate the adverse effects of DEHP on the lung during sensitization, we established an ovalbumin (OVA)-sensitized mouse model exposed to DEHP and performed 16S rDNA gene sequencing, miRNA sequencing, and correlation analysis. Our results showed that DEHP aggravated the immune disorder in OVA-sensitized mice, which was mainly characterized by an increase in the proportion of Th2 lymphocytes, and further enhanced OVA-induced airway inflammation without promoting pulmonary fibrosis. Compared with the OVA group, DEHP interfered with the lung microbial community, making Proteobacteria the dominant phylum, while Bacteroidetes were significantly reduced. Differentially expressed miRNAs were enriched in the PI3K/AKT pathway, which was closely related to immune function and airway inflammation. The expression of miR-146b-5p was elevated in the DEHP group, which was positively correlated with the proportion of Th2 cells and significantly negatively correlated with the abundance of Bacteroidetes. The results indicate that DEHP may interfere with the expression of miR-146b-5p, affect the composition of the lung microbiota, induce an imbalance in T cells, and lead to immune disorders and airway inflammation. The current study uses multi-omics to reveal the potential link between the plasticizer DEHP and allergic diseases and provides new insights into the ecotoxicology of environmental exposures to DEHP.

Extracellular and Intracellular Signaling for Neuronal Polarity.

Neurons are one of the highly polarized cells in the body. One of the fundamental issues in neuroscience is how neurons establish their polarity; therefore, this issue fascinates many scientists. Cultured neurons are useful tools for analyzing the mechanisms of neuronal polarization, and indeed, most of the molecules important in their polarization were identified using culture systems. However, we now know that the process of neuronal polarization in vivo differs in some respects from that in cultured neurons. One of the major differences is their surrounding microenvironment; neurons in vivo can be influenced by extrinsic factors from the microenvironment. Therefore, a major question remains: How are neurons polarized in vivo? Here, we begin by reviewing the process of neuronal polarization in culture conditions and in vivo. We also survey the molecular mechanisms underlying neuronal polarization. Finally, we introduce the theoretical basis of neuronal polarization and the possible involvement of neuronal polarity in disease and traumatic brain injury.

[Association between drug trough concentration and disease outcome before infliximab maintenance treatment in children with Crohn's disease]. / å ‹ç½—æ©ç— æ‚£å„¿è‹±å¤«åˆ©è¥¿å•æŠ—ç»´æŒæ²»ç–—å‰è¡€è¯æµ“åº¦ä¸Žç–¾ç— è½¬å½’çš„å ³ç³».

OBJECTIVES: To study the association between infliximab trough level (IFX-TL) prior to maintenance treatment and disease outcome in children with Crohn's disease (CD). METHODS: A retrospective analysis was performed on 35 children with CD who received induction therapy with infliximab (IFX) and the measurement of IFX-TL before maintenance treatment from August 2018 to November 2021. Clinical data and laboratory markers at baseline and before maintenance treatment were collected, and the association between outcome and IFX-TL was analyzed. RESULTS: The clinical remission group, endoscopic remission group, and combined remission group had a significantly higher IFX-TL level than the corresponding non-remission groups (P<0.05), and there was no significant difference in the IFX-TL level between the biological remission and non-biological remission groups (P>0.05). The receiver operating characteristic (ROC) curve showed that IFX-TL had an area under the ROC curve of 0.959 (95%CI: 0.894-1) in predicting clinical remission, with a sensitivity of 90% and a specificity of 100% at the optimal cutoff value of 2.3 µg/mL (P<0.001). CONCLUSIONS: Among children with CD receiving infliximab induction therapy, the children achieving clinical and endoscopic remission before maintenance treatment tend to have a higher level of IFX-TL. IFX-TL has a certain predictive value for clinical remission.

Lipopolysaccharide-induced DC-SIGN/TLR4 crosstalk activates NLRP3 inflammasomes via MyD88-independent signaling in gastric epithelial cells.

Abnormal pattern recognition receptor (PRR) signaling plays an important role in gastric mucosal damage caused by stomach microbiota; however, the underlying molecular mechanisms remain obscure. Here, we show that DC-SIGN, a surface phenotype marker of dendritic cells, is overexpressed in gastric epithelial cells facing LPS stimulation. NLRP3 expression in gastric epithelial cells are significantly increased and related to the degree of LPS stimulation. Furthermore, DC-SIGN could interact with TLR4, promote NLRP3 and related genes expression via MyD88-independent signaling pathway and regulate the secretion of IL-1ß and IL-18 in gastric epithelial cells. The results of flow cytometry analysis show that DC-SIGN primarily mediates Th1 differentiation when co-cultured with gastric epithelial cells. These results reveal that LPS-induced DC-SIGN expression modulates NLRP3 inflammasomes formation via MyD88-independent TLR4 signaling in gastric epithelial cell, and induces a Th1-predominant host immune response,these findings may indicate a new function of DC-SIGN in non-immune cells, and elucidate the diversity role of gastric epithelial cells in mechanism of immune damage caused by microbial flora.

Bifidobacterium breve M-16V alters the gut microbiota to alleviate OVA-induced food allergy through IL-33/ST2 signal pathway.

There has been a marked increase in life-threatening food allergy (FA). One hypothesis is that changes in bacterial communities may be key to FA. To better understand how gut microbiota regulates FA in humans, we established a mouse model with FA induced by ovalbumin. We found that the mice with FA had abnormal bacterial composition, accompanied by increased immunoglobulin G, immunoglobulin E, and interleukin-4/interferon-γ, and there existed a certain coherence between them. Interestingly, Bifidobacterium breve M-16V may alter the gut microbiota to alleviate the allergy symptoms by IL-33/ST2 signaling. Our results indicate that gut microbiota is essential for regulating FA to dietary antigens and demonstrate that intervention in bacterial community regulation may be therapeutically related to FA.

Probiotics as a functional food ingredient in allergic diseases: regulation of CD4+ T helper cell differentiation.

Allergic diseases are increasing worldwide, associating with increased health costs and decreased quality of life. Allergy is immune-related diseases caused by an allergic immune response to innocuous substance in the environment. At present, research has focussed on the study of the relevance to the microbiome and the phenotypes of allergy, including the relationships among the gastrointestinal microbiome, immune function, and allergic sensitisation. Probiotics as functional food ingredient are thought to secrete functional metabolites that have antibacterial effects on ameliorating intestinal health and CD4+ T helper cells-mediated immunity. This review will summarise the role of probiotics in the immune regulation and flora balance, highlighting recent advances in our understanding of the imbalance of Th subsets and cytokine leading to the immunopathology of allergic reactions. Finally, we discussed the unresolved problems and future research directions in order to promote the clinical application of probiotics immunotherapy.

[Clinical effect of sirolimus in treatment of blue rubber bleb nevus syndrome in children: a report of 2 cases and literature review].

To study the clinical effect of oral sirolimus in the treatment of children with blue rubber bleb nevus syndrome (BRBNS) in the gastrointestinal tract, a retrospective analysis was performed on the clinical data and follow-up results of two children with BRBNS treated by sirolimus. The two children with BRBNS had gastrointestinal bleeding and anemia and were treated with sirolimus at a dose of 1 mg/day as part of treatment. The plasma concentration of the drug was maintained between 2.5-12.0 ng/mL. The children showed disappearance of gastrointestinal bleeding and improvements in anemia and coagulation function, and blood transfusion could be stopped during treatment, with no obvious adverse drug reactions. PubMed, Wanfang Data, and CNKI were searched for related articles on sirolimus in the treatment of BRBNS. A total of 26 cases of children with BRBNS, aged 0-18 years, were obtained. With the addition of the 2 cases in this study, sirolimus treatment achieved a satisfactory clinical effect in all 28 cases. Sirolimus may be effective and safe in the treatment of children with BRBNS, and further prospective studies are needed to evaluate the long-term efficacy of this drug.

Neuronal polarization.

Neurons are highly polarized cells with structurally and functionally distinct processes called axons and dendrites. This polarization underlies the directional flow of information in the central nervous system, so the establishment and maintenance of neuronal polarization is crucial for correct development and function. Great progress in our understanding of how neurons establish their polarity has been made through the use of cultured hippocampal neurons, while recent technological advances have enabled in vivo analysis of axon specification and elongation. This short review and accompanying poster highlight recent advances in this fascinating field, with an emphasis on the signaling mechanisms underlying axon and dendrite specification in vitro and in vivo.

Study of disease phenotype and its association with prognosis of paediatric inflammatory bowel disease in China.

BACKGROUND: To investigate the unique features of inflammatory bowel disease (IBD) in children, we wanted to identify whether there might be a strong correlation between the disease phenotype and its prognosis at various ages in paediatric patients. METHODS: We collected data from patients diagnosed with IBD (ulcerative colitis (UC) or Crohn's disease (CD)) from 2002 to 2016. The diagnosis was made according to the Porto criteria and Paris Classification. Patient characteristics, clinical manifestations and treatments were collected. Risk factors for surgery, mortality and relapse were analysed by Cox proportional hazard models. RESULTS: Of the 143 patients, 113 had CD, and 30 had UC; there were 89 males and 54 females with a median age of 9 years (y). Thirteen patients in the 0-2 y group were identified as having mutations in IL-10 receptor A, and this mutation was significantly more common in this age group than in 3-9 and 10-16 y patients. The risk factor for surgery was the B3 phenotype; risk factors for death were age 0-2 y and B3 phenotype; 0-2 y, B3 phenotype and steroid dependency were risk factors for early relapse. CONCLUSIONS: Clinical manifestations of the onset of IBD in infants and toddlers were extensive and aggressive and were closely associated with early relapse and death. It is of particular interest that some of these patients developed IBD due to monogenic disorders; thus, introduction of genetic testing is essential for these patients.

Runt-related Transcription Factor 1 (RUNX1) Binds to p50 in Macrophages and Enhances TLR4-triggered Inflammation and Septic Shock.

An appropriate inflammatory response plays critical roles in eliminating pathogens, whereas an excessive inflammatory response can cause tissue damage. Runt-related transcription factor 1 (RUNX1), a master regulator of hematopoiesis, plays critical roles in T cells; however, its roles in Toll-like receptor 4 (TLR4)-mediated inflammation in macrophages are unclear. Here, we demonstrated that upon TLR4 ligand stimulation by lipopolysaccharide (LPS), macrophages reduced the expression levels of RUNX1 Silencing of Runx1 attenuated the LPS-induced IL-1ß and IL-6 production levels, but the TNF-α levels were not affected. Overexpression of RUNX1 promoted IL-1ß and IL-6 production in response to LPS stimulation. Moreover, RUNX1 interacted with the NF-κB subunit p50, and coexpression of RUNX1 with p50 further enhanced the NF-κB luciferase activity. Importantly, treatment with the RUNX1 inhibitor, Ro 5-3335, protected mice from LPS-induced endotoxic shock and substantially reduced the IL-6 levels. These findings suggest that RUNX1 may be a new potential target for resolving TLR4-associated uncontrolled inflammation and preventing sepsis.

Targeted Gene Next-Generation Sequencing in Chinese Children with Chronic Pancreatitis and Acute Recurrent Pancreatitis.

OBJECTIVE: To identify causal mutations in certain genes in children with acute recurrent pancreatitis (ARP) or chronic pancreatitis (CP). STUDY DESIGN: After patients were enrolled (CP, 55; ARP, 14) and their clinical characteristics were investigated, we performed next-generation sequencing to detect nucleotide variations among the following 10 genes: cationic trypsinogen protease serine 1 (PRSS1), serine protease inhibitor, Kazal type 1 (SPINK1), cystic fibrosis transmembrane conductance regulator gene (CFTR), chymotrypsin C (CTRC), calcium-sensing receptor (CASR), cathepsin B (CTSB), keratin 8 (KRT8), CLAUDIN 2 (CLDN2), carboxypeptidase A1 (CPA1), and ATPase type 8B member 1 (ATP8B1). Mutations were searched against online databases to obtain information on the cause of the diseases. Certain novel mutations were analyzed using the SIFT2 and Polyphen-2 to predict the effect on protein function. RESULTS: There were 45 patients with CP and 10 patients with ARP who harbored 1 or more mutations in these genes; 45 patients had at least 1 mutation related to pancreatitis. Mutations were observed in the PRSS1, SPINK1, and CFTR genes in 17 patients, the CASR gene in 5 patients, and the CTSB, CTRC, and KRT8 genes in 1 patient. Mutations were not found in the CLDN, CPA1, or ATP8B1 genes. We found that mutations in SPINK1 may increase the risk of pancreatic duct stones (OR, 11.07; P = .003). The patients with CFTR mutations had a higher level of serum amylase (316.0 U/L vs 92.5 U/L; P = .026). CONCLUSION: Mutations, especially those in PRSS1, SPINK1, and CFTR, accounted for the major etiologies in Chinese children with CP or ARP. Children presenting mutations in the SPINK1 gene may have a higher risk of developing pancreatic duct stones.

Radial Glial Cell-Neuron Interaction Directs Axon Formation at the Opposite Side of the Neuron from the Contact Site.

How extracellular cues direct axon-dendrite polarization in mouse developing neurons is not fully understood. Here, we report that the radial glial cell (RGC)-cortical neuron interaction directs axon formation at the opposite side of the neuron from the contact site. N-cadherin accumulates at the contact site between the RGC and cortical neuron. Inhibition of the N-cadherin-mediated adhesion decreases this oriented axon formation in vitro, and disrupts the axon-dendrite polarization in vivo. Furthermore, the RGC-neuron interaction induces the polarized distribution of active RhoA at the contacting neurite and active Rac1 at the opposite neurite. Inhibition of Rho-Rho-kinase signaling in a neuron impairs the oriented axon formation in vitro, and prevents axon-dendrite polarization in vivo. Collectively, these results suggest that the N-cadherin-mediated radial glia-neuron interaction determines the contacting neurite as the leading process for radial glia-guided neuronal migration and directs axon formation to the opposite side acting through the Rho family GTPases.

DC-SIGN expression on podocytes and its role in inflammatory immune response of lupus nephritis.

Podocytes, the main target of immune complex, participate actively in the development of glomerular injury as immune cells. Dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN) is an innate immune molecular that has an immune recognition function, and is involved in mediation of cell adhesion and immunoregulation. Here we explored the expression of DC-SIGN on podocytes and its role in immune and inflammatory responses in lupus nephritis (LN). Expression of DC-SIGN and immunoglobulin (Ig)G1 was observed in glomeruli of LN patients. DC-SIGN was co-expressed with nephrin on podocytes. Accompanied by increased proteinuria of LN mice, DC-SIGN and IgG1 expressions were observed in the glomeruli from 20 weeks, and the renal function deteriorated up to 24 weeks. Mice with anti-DC-SIGN antibody showed reduced proteinuria and remission of renal function. After the podocytes were stimulated by serum of LN mice in vitro, the expression of DC-SIGN, major histocompatibility complex (MHC) class II and CD80 was up-regulated, stimulation of T cell proliferation was enhanced and the interferon (IFN)-γ/interleukin (IL)-4 ratio increased. However, anti-DC-SIGN antibody treatment reversed these events. These results suggested that podocytes in LN can exert DC-like function through their expression of DC-SIGN, which may be involved in immune and inflammatory responses of renal tissues. However, blockage of DC-SIGN can inhibit immune functions of podocytes, which may have preventive and therapeutic effects.

[Therapeutic effects of zinc supplement as adjunctive therapy in infants and young children with rotavirus enteritis].

OBJECTIVE: To investigate the therapeutic effects of oral zinc supplement in infants and young children with rotavirus enteritis, and its preventive effects against diarrhea recurrence within 3 months after treatment. METHODS: A total of 103 infants and young children with rotavirus enteritis were randomly divided into zinc supplement group (n=51) and conventional treatment group (n=52). Both groups were equally treated with a comprehensive therapy, besides which the zinc supplement group received zinc gluconate granules for 10 days. The treatment outcomes were examined at 72 hours after treatment, and the time required for the disappearance of positive symptoms and the recovery of injured extra-intestinal organs were determined. In addition, these patients were followed up for 3 months to determine the incidence of diarrhea recurrence after treatment. RESULTS: The overall response rate in the zinc supplement group was significantly higher than that in the conventional treatment group (90% vs 75%; P<0.05). The durations of diarrhea, high fever, and vomiting in the zinc supplement group were significantly shorter than that in the conventional treatment group (P<0.05). In addition, the recurrence rate of diarrhea and the incidence of severe diarrhea within 3 months after treatment in the zinc supplement group were significantly lower than in the conventional treatment group (P<0.05). CONCLUSIONS: Oral zinc supplement as adjunctive therapy is effective in treating infants and young children with rotavirus enteritis, and reducing the incidence and severity of diarrhea recurrence in the subsequent 3 months.

ERK2-mediated phosphorylation of Par3 regulates neuronal polarization.

Axon formation is one of the most important events in neuronal polarization and is regulated by signaling molecules involved in cytoskeletal rearrangement and protein transport. We previously found that Partition-defective 3 (Par3) is associated with KIF3A (kinesin-2) and is transported into the nascent axon in a KIF3A-dependent fashion. Par3 interacts with the Rac-specific guanine nucleotide-exchange factors (GEFs) Tiam1/2, which activate Rac1, and participates in axon formation in cultured hippocampal neurons. However, the regulatory mechanism of the Par3-KIF3A interaction is poorly understood, and the role of Par3 in neuronal polarization in vivo remains elusive. Here, we found that extracellular signal-regulated kinase 2 (ERK2) directly interacts with Par3, that ERK2 phosphorylates Par3 at Ser-1116, and that the phosphorylated Par3 accumulates at the axonal tips in a manner dependent upon ERK2 activity. The phosphorylation of Par3 by ERK2 inhibited the interaction of Par3 with KIF3A but not with the other Par3 partners, including Par6 and aPKC. The phosphomimic mutant of Par3 (Par3-S1116D) showed less binding activity with the KIF3s and slower transport in the axons. The knockdown of Par3 by RNA interference impaired neuronal polarization, which was rescued with RNAi-resistant Par3, but not with the phosphomimic Par3 mutant, in cultured rat hippocampal neurons and mouse cortical projection neurons in vivo. These results suggest that ERK2 phosphorylates Par3 and inhibits its binding with KIF3A, thereby controlling Par3 transport and neuronal polarity.

Notch signaling and Bsh homeodomain activity are integrated to diversify Drosophila lamina neuron types.

Notch signaling is an evolutionarily conserved pathway for specifying binary neuronal fates, yet how it specifies different fates in different contexts remains elusive. In our accompanying paper, using the Drosophila lamina neuron types (L1-L5) as a model, we show that the primary homeodomain transcription factor (HDTF) Bsh activates secondary HDTFs Ap (L4) and Pdm3 (L5) and specifies L4/L5 neuronal fates. Here we test the hypothesis that Notch signaling enables Bsh to differentially specify L4 and L5 fates. We show asymmetric Notch signaling between newborn L4 and L5 neurons, but they are not siblings; rather, Notch signaling in L4 is due to Delta expression in adjacent L1 neurons. While Notch signaling and Bsh expression are mutually independent, Notch is necessary and sufficient for Bsh to specify L4 fate over L5. The NotchON L4, compared to NotchOFF L5, has a distinct open chromatin landscape which allows Bsh to bind distinct genomic loci, leading to L4-specific identity gene transcription. We propose a novel model in which Notch signaling is integrated with the primary HDTF activity to diversify neuron types by directly or indirectly generating a distinct open chromatin landscape that constrains the pool of genes that a primary HDTF can activate.

Homeodomain proteins hierarchically specify neuronal diversity and synaptic connectivity.

How our brain generates diverse neuron types that assemble into precise neural circuits remains unclear. Using Drosophila lamina neuron types (L1-L5), we show that the primary homeodomain transcription factor (HDTF) brain-specific homeobox (Bsh) is initiated in progenitors and maintained in L4/L5 neurons to adulthood. Bsh activates secondary HDTFs Ap (L4) and Pdm3 (L5) and specifies L4/L5 neuronal fates while repressing the HDTF Zfh1 to prevent ectopic L1/L3 fates (control: L1-L5; Bsh-knockdown: L1-L3), thereby generating lamina neuronal diversity for normal visual sensitivity. Subsequently, in L4 neurons, Bsh and Ap function in a feed-forward loop to activate the synapse recognition molecule DIP-ß, thereby bridging neuronal fate decision to synaptic connectivity. Expression of a Bsh:Dam, specifically in L4, reveals Bsh binding to the DIP-ß locus and additional candidate L4 functional identity genes. We propose that HDTFs function hierarchically to coordinate neuronal molecular identity, circuit formation, and function. Hierarchical HDTFs may represent a conserved mechanism for linking neuronal diversity to circuit assembly and function.