In vitro and in vivo modeling systems of supratentorial ependymomas.

Ependymomas are rare brain tumors that can occur in both children and adults. Subdivided by the tumors' initial location, ependymomas develop in the central nervous system in the supratentorial or infratentorial/posterior fossa region, or the spinal cord. Supratentorial ependymomas (ST-EPNs) are predominantly characterized by common driver gene fusions such as ZFTA and YAP1 fusions. Some variants of ST-EPNs carry a high overall survival rate. In poorly responding ST-EPN variants, high levels of inter- and intratumoral heterogeneity, limited therapeutic strategies, and tumor recurrence are among the reasons for poor patient outcomes with other ST-EPN subtypes. Thus, modeling these molecular profiles is key in further studying tumorigenesis. Due to the scarcity of patient samples, the development of preclinical in vitro and in vivo models that recapitulate patient tumors is imperative when testing therapeutic approaches for this rare cancer. In this review, we will survey ST-EPN modeling systems, addressing the strengths and limitations, application for therapeutic targeting, and current literature findings.

SOX9 switch links regeneration to fibrosis at the single-cell level in mammalian kidneys.

The steps governing healing with or without fibrosis within the same microenvironment are unclear. After acute kidney injury (AKI), injured proximal tubular epithelial cells activate SOX9 for self-restoration. Using a multimodal approach for a head-to-head comparison of injury-induced SOX9 lineages, we identified a dynamic SOX9 switch in repairing epithelia. Lineages that regenerated epithelia silenced SOX9 and healed without fibrosis (SOX9on-off). By contrast, lineages with unrestored apicobasal polarity maintained SOX9 activity in sustained efforts to regenerate, which were identified as a SOX9on-on Cadherin6pos cell state. These reprogrammed cells generated substantial single-cell WNT activity to provoke a fibroproliferative response in adjacent fibroblasts, driving AKI to chronic kidney disease. Transplanted human kidneys displayed similar SOX9/CDH6/WNT2B responses. Thus, we have uncovered a sensor of epithelial repair status, the activity of which determines regeneration with or without fibrosis.

Increasing Ciliary ARL13B Expression Drives Active and Inhibitor-Resistant Smoothened and GLI into Glioma Primary Cilia.

ADP-ribosylation factor-like protein 13B (ARL13B), a regulatory GTPase and guanine exchange factor (GEF), enriches in primary cilia and promotes tumorigenesis in part by regulating Smoothened (SMO), GLI, and Sonic Hedgehog (SHH) signaling. Gliomas with increased ARL13B, SMO, and GLI2 expression are more aggressive, but the relationship to cilia is unclear. Previous studies have showed that increasing ARL13B in glioblastoma cells promoted ciliary SMO accumulation, independent of exogenous SHH addition. Here, we show that SMO accumulation is due to increased ciliary, but not extraciliary, ARL13B. Increasing ARL13B expression promotes the accumulation of both activated SMO and GLI2 in glioma cilia. ARL13B-driven increases in ciliary SMO and GLI2 are resistant to SMO inhibitors, GDC-0449, and cyclopamine. Surprisingly, ARL13B-induced changes in ciliary SMO/GLI2 did not correlate with canonical changes in downstream SHH pathway genes. However, glioma cell lines whose cilia overexpress WT but not guanine exchange factor-deficient ARL13B, display reduced INPP5e, a ciliary membrane component whose depletion may favor SMO/GLI2 enrichment. Glioma cells overexpressing ARL13B also display reduced ciliary intraflagellar transport 88 (IFT88), suggesting that altered retrograde transport could further promote SMO/GLI accumulation. Collectively, our data suggest that factors increasing ARL13B expression in glioma cells may promote both changes in ciliary membrane characteristics and IFT proteins, leading to the accumulation of drug-resistant SMO and GLI. The downstream targets and consequences of these ciliary changes require further investigation.

Differential Susceptibility of Ex Vivo Primary Glioblastoma Tumors to Oncolytic Effect of Modified Zika Virus.

Glioblastoma (GBM), the most common primary malignant brain tumor, is a highly lethal form of cancer with a very limited set of treatment options. High heterogeneity in the tumor cell population and the invasive nature of these cells decrease the likely efficacy of traditional cancer treatments, thus requiring research into novel treatment options. The use of oncolytic viruses as potential therapeutics has been researched for some time. Zika virus (ZIKV) has demonstrated oncotropism and oncolytic effects on GBM stem cells (GSCs). To address the need for safe and effective GBM treatments, we designed an attenuated ZIKV strain (ZOL-1) that does not cause paralytic or neurological diseases in mouse models compared with unmodified ZIKV. Importantly, we found that patient-derived GBM tumors exhibited susceptibility (responders) and non-susceptibility (non-responders) to ZOL-1-mediated tumor cell killing, as evidenced by differential apoptotic cell death and cell viability upon ZOL-1 treatment. The oncolytic effect observed in responder cells was seen both in vitro in neurosphere models and in vivo upon xenograft. Finally, we observed that the use of ZOL-1 as combination therapy with multiple PI3K-AKT inhibitors in non-responder GBM resulted in enhanced chemotherapeutic efficacy. Altogether, this study establishes ZOL-1 as a safe and effective treatment against GBM and provides a foundation to conduct further studies evaluating its potential as an effective adjuvant with other chemotherapies and kinase inhibitors.

Modeling Brain Tumors In Vivo Using Electroporation-Based Delivery of Plasmid DNA Representing Patient Mutation Signatures.

Tumor models are critical for the preclinical testing of brain tumors in terms of exploring new, more efficacious treatments. With significant interest in immunotherapy, it is even more critical to have a consistent, clinically pertinent, immunocompetent mouse model to examine the tumor and immune cell populations in the brain and their response to treatment. While most preclinical models utilize orthotopic transplantation of established tumor cell lines, the modeling system presented here allows for a "personalized" representation of patient-specific tumor mutations in a gradual, yet effective development from DNA constructs inserted into dividing neural precursor cells (NPCs) in vivo. DNA constructs feature the mosaic analysis with the dual-recombinase-mediated cassette exchange (MADR) method, allowing for single-copy, somatic mutagenesis of driver mutations. Using newborn mouse pups between birth and 3 days old, NPCs are targeted by taking advantage of these dividing cells lining the lateral ventricles. Microinjection of DNA plasmids (e.g., MADR-derived, transposons, CRISPR-directed sgRNA) into the ventricles is followed by electroporation using paddles that surround the rostral region of the head. Upon electrical stimulation, the DNA is taken up into the dividing cells, with the potential of integrating into the genome. The use of this method has successfully been demonstrated in developing both pediatric and adult brain tumors, including the most common malignant brain tumor, glioblastoma. This article discusses and demonstrates the different steps of developing a brain tumor model using this technique, including the procedure of anesthetizing young mouse pups, to microinjection of the plasmid mix, followed by electroporation. With this autochthonous, immunocompetent mouse model, researchers will have the ability to expand preclinical modeling approaches, in efforts to improve and examine efficacious cancer treatment.

Tetracycline-Inducible and Reversible Stable Gene Expression in Human iPSC-Derived Neural Progenitors and in the Postnatal Mouse Brain.

Our group has developed several approaches for stable, non-viral integration of inducible transgenic elements into the genome of mammalian cells. Specifically, a piggyBac tetracycline-inducible genetic element of interest (pB-tet-GOI) plasmid system allows for stable piggyBac transposition-mediated integration into cells, identification of cells that have been transfected using a fluorescent nuclear reporter, and robust transgene activation or suppression upon the addition of doxycycline (dox) to the cell culture or the diet of the animal. Furthermore, the addition of luciferase downstream of the target gene allows for quantitative assessment of gene activity in a non-invasive manner. More recently, we have developed a transgenic system as an alternative to piggyBac called mosaic analysis by dual recombinase-mediated cassette exchange (MADR), as well as additional in vitro transfection techniques and in vivo dox chow applications. The protocols herein provide instructions for the use of this system in cell lines and in the neonatal mouse brain. © 2023 Wiley Periodicals LLC. Basic Protocol 1: Cloning of respective genetic element of interest (GOI) into response plasmid Basic Protocol 2: In vitro nucleofection of iPSC-derived human/mouse neural progenitor cells and subsequent derivation of stable inducible cell lines Alternate Protocol: In vitro electroporation of iPSC-derived human/mouse neural progenitor cells Support Protocol: Recovery stage after in vitro transfection Basic Protocol 3: Adding doxycycline to cells to induce/reverse GOI Basic Protocol 4: Assessing gene expression in vitro by non-invasive bioluminescence imaging of luciferase activity.

Murine-Derived Glioma Organoids and Cell Line Culture Systems.

Research models in cancer have greatly evolved in the last decade, with the advent of several new methods both in vitro and in vivo. While in vivo models remain the gold standard for preclinical studies, these methods present a series of disadvantages such as a high cost and long periods of time to produce results compared with in vitro models. We have previously developed a method named Mosaic Analysis by Dual Recombinase-mediated cassette exchange (MADR) that generates autochthonous gliomas in immunocompetent mice through the transgenesis of personalized driver mutations, which highly mimic the spatial and temporal tumor development of their human counterparts. Due to the control of single-copy expression of transgenes, it allows for comparing the visualization of tumor cells and non-tumor cells. Here we describe a method to generate murine-derived glioma organoids (MGOs) and cell line cultures from these murine models by physical and enzymatic methods for in vitro downstream applications. Tumor cells can be readily distinguished from non-tumor cell populations, in both organoids and monolayer cell cultures, and isolated due to the use of personalized fluorescent reporter transgenes. © 2023 Wiley Periodicals LLC. Basic Protocol 1: Generation of 3D murine-derived glioma organoids Basic Protocol 2: Generation of 2D glioma monolayer cell lines.

Pediatric low-grade glioma models: advances and ongoing challenges.

Pediatric low-grade gliomas represent the most common childhood brain tumor class. While often curable, some tumors fail to respond and even successful treatments can have life-long side effects. Many clinical trials are underway for pediatric low-grade gliomas. However, these trials are expensive and challenging to organize due to the heterogeneity of patients and subtypes. Advances in sequencing technologies are helping to mitigate this by revealing the molecular landscapes of mutations in pediatric low-grade glioma. Functionalizing these mutations in the form of preclinical models is the next step in both understanding the disease mechanisms as well as for testing therapeutics. However, such models are often more difficult to generate due to their less proliferative nature, and the heterogeneity of tumor microenvironments, cell(s)-of-origin, and genetic alterations. In this review, we discuss the molecular and genetic alterations and the various preclinical models generated for the different types of pediatric low-grade gliomas. We examined the different preclinical models for pediatric low-grade gliomas, summarizing the scientific advances made to the field and therapeutic implications. We also discuss the advantages and limitations of the various models. This review highlights the importance of preclinical models for pediatric low-grade gliomas while noting the challenges and future directions of these models to improve therapeutic outcomes of pediatric low-grade gliomas.

First-line Immune Checkpoint Inhibitor Combinations in Metastatic Renal Cell Carcinoma: Where Are We Going, Where Have We Been?

The combination of targeted therapy and immunotherapy in the treatment of metastatic renal cell carcinoma (mRCC) has significantly improved outcomes for many patients. There are multiple FDA-approved regimens for the frontline setting based on numerous randomized Phase III trials. Despite these efforts, there remains a conundrum of identifying a biomarker-driven approach for these patients and it is unclear how to predict which patients are most likely to respond to these agents. This is due, in part, to an incomplete understanding of how these drug combinations work. The use of tyrosine kinase inhibitors that have multiple 'off-target' effects may lend themselves to the benefits observed when given in combination with immunotherapy. Further, targeting multiple clones within a patient's heterogenic tumor that are responsive to targeted therapy and others that are responsive to immunotherapy may also explain some level of improved response rates to the combination approaches compared to monotherapies. This review highlights the 5 FDA-approved regimens for mRCC in the frontline setting and offers insights into potential mechanisms for improved outcomes seen in these combination approaches.

SF3B1 inhibition disrupts malignancy and prolongs survival in glioblastoma patients through BCL2L1 splicing and mTOR/ß-catenin pathways imbalances.

BACKGROUND: Glioblastoma is one of the most devastating cancer worldwide based on its locally aggressive behavior and because it cannot be cured by current therapies. Defects in alternative splicing process are frequent in cancer. Recently, we demonstrated that dysregulation of the spliceosome is directly associated with glioma development, progression, and aggressiveness. METHODS: Different human cohorts and a dataset from different glioma mouse models were analyzed to determine the mutation frequency as well as the gene and protein expression levels between tumor and control samples of the splicing-factor-3B-subunit-1 (SF3B1), an essential and druggable spliceosome component. SF3B1 expression was also explored at the single-cell level across all cell subpopulations and transcriptomic programs. The association of SF3B1 expression with relevant clinical data (e.g., overall survival) in different human cohorts was also analyzed. Different functional (proliferation/migration/tumorspheres and colonies formation/VEGF secretion/apoptosis) and mechanistic (gene expression/signaling pathways) assays were performed in three different glioblastomas cell models (human primary cultures and cell lines) in response to SF3B1 blockade (using pladienolide B treatment). Moreover, tumor progression and formation were monitored in response to SF3B1 blockade in two preclinical xenograft glioblastoma mouse models. RESULTS: Our data provide novel evidence demonstrating that the splicing-factor-3B-subunit-1 (SF3B1, an essential and druggable spliceosome component) is low-frequency mutated in human gliomas (~ 1 %) but widely overexpressed in glioblastoma compared with control samples from the different human cohorts and mouse models included in the present study, wherein SF3B1 levels are associated with key molecular and clinical features (e.g., overall survival, poor prognosis and/or drug resistance). Remarkably, in vitro and in vivo blockade of SF3B1 activity with pladienolide B drastically altered multiple glioblastoma pathophysiological processes (i.e., reduction in proliferation, migration, tumorspheres formation, VEGF secretion, tumor initiation and increased apoptosis) likely by suppressing AKT/mTOR/ß-catenin pathways, and an imbalance of BCL2L1 splicing. CONCLUSIONS: Together, we highlight SF3B1 as a potential diagnostic and prognostic biomarker and an efficient pharmacological target in glioblastoma, offering a clinically relevant opportunity worth to be explored in humans.

Neurosurgery at the crossroads of immunology and nanotechnology. New reality in the COVID-19 pandemic.

Neurosurgery as one of the most technologically demanding medical fields rapidly adapts the newest developments from multiple scientific disciplines for treating brain tumors. Despite half a century of clinical trials, survival for brain primary tumors such as glioblastoma (GBM), the most common primary brain cancer, or rare ones including primary central nervous system lymphoma (PCNSL), is dismal. Cancer therapy and research have currently shifted toward targeted approaches, and personalized therapies. The orchestration of novel and effective blood-brain barrier (BBB) drug delivery approaches, targeting of cancer cells and regulating tumor microenvironment including the immune system are the key themes of this review. As the global pandemic due to SARS-CoV-2 virus continues, neurosurgery and neuro-oncology must wrestle with the issues related to treatment-related immune dysfunction. The selection of chemotherapeutic treatments, even rare cases of hypersensitivity reactions (HSRs) that occur among immunocompromised people, and number of vaccinations they have to get are emerging as a new chapter for modern Nano neurosurgery.

Integrated single-cell transcriptome analysis reveals heterogeneity of esophageal squamous cell carcinoma microenvironment.

The tumor microenvironment is a highly complex ecosystem of diverse cell types, which shape cancer biology and impact the responsiveness to therapy. Here, we analyze the microenvironment of esophageal squamous cell carcinoma (ESCC) using single-cell transcriptome sequencing in 62,161 cells from blood, adjacent nonmalignant and matched tumor samples from 11 ESCC patients. We uncover heterogeneity in most cell types of the ESCC stroma, particularly in the fibroblast and immune cell compartments. We identify a tumor-specific subset of CST1+ myofibroblasts with prognostic values and potential biological significance. CST1+ myofibroblasts are also highly tumor-specific in other cancer types. Additionally, a subset of antigen-presenting fibroblasts is revealed and validated. Analyses of myeloid and T lymphoid lineages highlight the immunosuppressive nature of the ESCC microenvironment, and identify cancer-specific expression of immune checkpoint inhibitors. This work establishes a rich resource of stromal cell types of the ESCC microenvironment for further understanding of ESCC biology.

In vivo discovery of RNA proximal proteins via proximity-dependent biotinylation.

RNA molecules function as messenger RNAs (mRNAs) that encode proteins and noncoding transcripts that serve as adaptor molecules, structural components, and regulators of genome organization and gene expression. Their function and regulation are largely mediated by RNA binding proteins (RBPs). Here we present RNA proximity labelling (RPL), an RNA-centric method comprising the endonuclease-deficient Type VI CRISPR-Cas protein dCas13b fused to engineered ascorbate peroxidase APEX2. RPL discovers target RNA proximal proteins in vivo via proximity-based biotinylation. RPL applied to U1 identified proteins involved in both U1 canonical and noncanonical functions. Profiling of poly(A) tail proximal proteins uncovered expected categories of RBPs and provided additional evidence for 5'-3' proximity and unexplored subcellular localizations of poly(A)+ RNA. Our results suggest that RPL allows rapid identification of target RNA binding proteins in native cellular contexts, and is expected to pave the way for discovery of novel RNA-protein interactions important for health and disease.

RELA Fusion-Positive Ependymoma in a Child with Down Syndrome: A Case Report.

INTRODUCTION: Down syndrome (DS) is the most common multiple malformation syndrome in humans and is associated with an increased risk of childhood malignancy, particularly leukemia. Incidence of brain tumors in patients with DS is limited to sporadic cases. We report the first case of a RELA fusion-positive ependymoma in a 3-year-old boy with DS. CASE PRESENTATION: Imaging prompted by new left-sided hemiparesis demonstrated an 8-cm hemorrhagic right temporal-parietal mass. Subsequent image-complete resection confirmed a RELA fusion-positive anaplastic ependymoma with 90% OLIG2 staining. Postoperatively, the patient, unfortunately, experienced fatal recurrence and drop metastases with leptomeningeal involvement. CONCLUSION: To our knowledge, this is the first reported case of a confirmed RELA fusion-positive ependymoma in a child with DS. We discuss this finding in the context of intracranial tumors in children with DS, as well as the finding of 90% positive OLIG2 expression and its potential as a prognostic marker.

A Transcriptional Regulatory Loop of Master Regulator Transcription Factors, PPARG, and Fatty Acid Synthesis Promotes Esophageal Adenocarcinoma.

Although obesity is one of the strongest risk factors for esophageal adenocarcinoma, the molecular mechanisms underlying this association remain unclear. We recently identified four esophageal adenocarcinoma-specific master regulator transcription factors (MRTF) ELF3, KLF5, GATA6, and EHF. In this study, gene-set enrichment analysis of both esophageal adenocarcinoma patient samples and cell line models unbiasedly underscores fatty acid synthesis as the central pathway downstream of three MRTFs (ELF3, KLF5, GATA6). Further characterizations unexpectedly identified a transcriptional feedback loop between MRTF and fatty acid synthesis, which mutually activated each other through the nuclear receptor, PPARG. MRTFs cooperatively promoted PPARG transcription by directly regulating its promoter and a distal esophageal adenocarcinoma-specific enhancer, leading to PPARG overexpression in esophageal adenocarcinoma. PPARG was also elevated in Barrett's esophagus, a recognized precursor to esophageal adenocarcinoma, implying that PPARG might play a role in the intestinal metaplasia of esophageal squamous epithelium. Upregulation of PPARG increased de novo synthesis of fatty acids, phospholipids, and sphingolipids as revealed by mass spectrometry-based lipidomics. Moreover, ChIP-seq, 4C-seq, and a high-fat diet murine model together characterized a novel, noncanonical, and cancer-specific function of PPARG in esophageal adenocarcinoma. PPARG directly regulated the ELF3 super-enhancer, subsequently activating the transcription of other MRTFs through an interconnected regulatory circuitry. Together, elucidation of this novel transcriptional feedback loop of MRTF/PPARG/fatty acid synthesis advances our understanding of the mechanistic foundation for epigenomic dysregulation and metabolic alterations in esophageal adenocarcinoma. More importantly, this work identifies a potential avenue for prevention and early intervention of esophageal adenocarcinoma by blocking this feedback loop. SIGNIFICANCE: These findings elucidate a transcriptional feedback loop linking epigenomic dysregulation and metabolic alterations in esophageal adenocarcinoma, indicating that blocking this feedback loop could be a potential therapeutic strategy in high-risk individuals.

De Novo Generation of Murine and Human MADR Recipient Cell Lines for Locus-Specific, Stable Integration of Transgenic Elements.

Mosaic analysis by dual recombinase-mediated cassette exchange (MADR) is a technology that allows stable and locus-specific integration of transgenic elements into recipient cells carrying loxP and FRT sites. Nevertheless, most cell lines lack these recombination-specific sites. This protocol describes a method to introduce the minimum requirements into cells, leading to the generation of de novo primary MADR recipient cells or MADR "Proxy" cells. These cell lines allow the combinatorial use of a wide range of transgenic elements through MADR. For complete details on the use and execution of this protocol, please refer to Kim et al. (2019).

Preparation, Assembly, and Transduction of Transgenic Elements Using Mosaic Analysis with Dual Recombinases (MADR).

This protocol focuses on the cloning and stable integration of sequences of interest by the use of a mosaic analysis with dual recombinases (MADR) plasmid that includes fusion proteins or independent proteins under the control of 2A peptide or IRES elements. Additionally, we describe how to generate a neural stem cell culture from Gt(ROSA)26Sortm4(ACTB-tdTomato, EGFP)Luo/J mice, and validate the MADR plasmids in vitro and in vivo by neonatal mouse brain electroporation. This protocol can be generalized to analyze any transgenic element using MADR technology. For complete details on the use and execution of this protocol, please refer to Kim et al. (2019).

Splicing machinery dysregulation drives glioblastoma development/aggressiveness: oncogenic role of SRSF3.

Glioblastomas remain the deadliest brain tumour, with a dismal ∼12-16-month survival from diagnosis. Therefore, identification of new diagnostic, prognostic and therapeutic tools to tackle glioblastomas is urgently needed. Emerging evidence indicates that the cellular machinery controlling the splicing process (spliceosome) is altered in tumours, leading to oncogenic splicing events associated with tumour progression and aggressiveness. Here, we identify for the first time a profound dysregulation in the expression of relevant spliceosome components and splicing factors (at mRNA and protein levels) in well characterized cohorts of human high-grade astrocytomas, mostly glioblastomas, compared to healthy brain control samples, being SRSF3, RBM22, PTBP1 and RBM3 able to perfectly discriminate between tumours and control samples, and between proneural-like or mesenchymal-like tumours versus control samples from different mouse models with gliomas. Results were confirmed in four additional and independent human cohorts. Silencing of SRSF3, RBM22, PTBP1 and RBM3 decreased aggressiveness parameters in vitro (e.g. proliferation, migration, tumorsphere-formation, etc.) and induced apoptosis, especially SRSF3. Remarkably, SRSF3 was correlated with patient survival and relevant tumour markers, and its silencing in vivo drastically decreased tumour development and progression, likely through a molecular/cellular mechanism involving PDGFRB and associated oncogenic signalling pathways (PI3K-AKT/ERK), which may also involve the distinct alteration of alternative splicing events of specific transcription factors controlling PDGFRB (i.e. TP73). Altogether, our results demonstrate a drastic splicing machinery-associated molecular dysregulation in glioblastomas, which could potentially be considered as a source of novel diagnostic and prognostic biomarkers as well as therapeutic targets for glioblastomas. Remarkably, SRSF3 is directly associated with glioblastoma development, progression, aggressiveness and patient survival and represents a novel potential therapeutic target to tackle this devastating pathology.

Rapid Generation of Somatic Mouse Mosaics with Locus-Specific, Stably Integrated Transgenic Elements.

In situ transgenesis methods such as viruses and electroporation can rapidly create somatic transgenic mice but lack control over copy number, zygosity, and locus specificity. Here we establish mosaic analysis by dual recombinase-mediated cassette exchange (MADR), which permits stable labeling of mutant cells expressing transgenic elements from precisely defined chromosomal loci. We provide a toolkit of MADR elements for combination labeling, inducible and reversible transgene manipulation, VCre recombinase expression, and transgenesis of human cells. Further, we demonstrate the versatility of MADR by creating glioma models with mixed reporter-identified zygosity or with "personalized" driver mutations from pediatric glioma. MADR is extensible to thousands of existing mouse lines, providing a flexible platform to democratize the generation of somatic mosaic mice. VIDEO ABSTRACT.

In utero electroporation-based translating ribosome affinity purification identifies age-dependent mRNA expression in cortical pyramidal neurons.

We combined translating ribosome affinity purification (TRAP) with in utero electroporation (IUE), called iTRAP to identify the molecular profile of specific neuronal populations during neonatal development without the need for viral approaches and FACS sorting. We electroporated a plasmid encoding EGFP-tagged ribosomal protein L10a at embryonic day (E) 14-15 to target layer 2-4 cortical neurons of the somatosensory cortex. At three postnatal (P) ages-P0, P7, and P14-when morphogenesis occurs and synapses are forming, TRAP and molecular profiling was performed from electroporated regions. We found that ribosome bound (Ribo)-mRNAs from ∼7300 genes were significantly altered over time and included classical neuronal genes known to decrease (e.g., Tbr1, Dcx) or increase (e.g., Eno2, Camk2a, Syn1) as neurons mature. This approach led to the identification of specific developmental patterns for Ribo-mRNAs not previously reported to be developmentally regulated in neurons, providing rationale for future examination of their role in selective biological processes. These include upregulation of Lynx1, Nrn1, Cntnap1 over time; downregulation of St8sia2 and Draxin; and bidirectional changes to Fkbp1b. iTRAP is a versatile approach that allows researchers to easily assess the molecular profile of specific neuronal populations in selective brain regions under various conditions, including overexpression and knockdown of target genes, and in disease settings.