Incidence of COVID-19 mRNA vaccine symptomatic breakthrough infections during Omicron circulation in adults with or without infection prior to vaccination.

OBJECTIVES: COVID-19 vaccine breakthrough infections were frequently reported during circulation of the Omicron variant. The ANRS|MIE CoviCompareP study investigated these infections in adults vaccinated and boosted with BNT162b2 [Pfizer-BioNTech] and with/without SARS-CoV-2 infection before vaccination. METHODS: In the first half of 2021, healthy adults (aged 18-45, 65-74 and 75 or older) received either one dose of BNT162b2 (n = 120) if they had a documented history of SARS-CoV-2 infection at least five months previously, or two doses (n = 147) if they had no history confirmed by negative serological tests. A first booster dose was administered at least 6 months after the primary vaccination, and a second booster dose, if any, was reported in the database. Neutralizing antibodies (NAbs) against the European (D614G) strain and the Omicron BA.1 variant were assessed up to 28 days after the first booster dose. A case-control analysis was performed for the 252 participants who were followed up in 2022, during the Omicron waves. RESULTS: From January to October 2022, 78/252 (31%) had a documented symptomatic breakthrough infection after full vaccination: 21/117 (18%) in those who had been infected before vaccination vs. 57/135 (42%) in those who had not. In a multivariate logistic regression model, factors associated with a lower risk of breakthrough infection were older age, a higher number of booster doses, and higher levels of Omicron BA.1 NAb titers in adults with infection before vaccination, but not in those without prior infection. CONCLUSION: Our results highlight the need to consider immune markers of protection in association with infection and vaccination history.

Neutralizing and enhancing monoclonal antibodies in SARS-CoV-2 convalescent patients: lessons from early variant infection and impact on shaping emerging variants.

Serological studies of COVID-19 convalescent patients have identified polyclonal lineage-specific and cross-reactive antibodies (Abs), with varying effector functions against virus variants. Individual specificities of anti-SARS-CoV-2 Abs and their impact on infectivity by other variants have been little investigated to date. Here, we dissected at a monoclonal level neutralizing and enhancing Abs elicited by early variants and how they affect infectivity of emerging variants. B cells from 13 convalescent patients originally infected by D614G or Alpha variants were immortalized to isolate 445 naturally-produced anti-SARS-CoV-2 Abs. Monoclonal antibodies (mAbs) were tested for their abilities to impact the cytopathic effect of D614G, Delta, and Omicron (BA.1) variants. Ninety-eight exhibited robust neutralization against at least one of the three variant types, while 309 showed minimal or no impact on infectivity. Thirty-eight mAbs enhanced infectivity of SARS-CoV-2. Infection with D614G/Alpha variants generated variant-specific (65 neutralizing Abs, 35 enhancing Abs) and cross-reactive (18 neutralizing Abs, 3 enhancing Abs) mAbs. Interestingly, among the neutralizing mAbs with cross-reactivity restricted to two of the three variants tested, none demonstrated specific neutralization of the Delta and Omicron variants. In contrast, cross-reactive mAbs enhancing infectivity (n = 3) were found exclusively specific to Delta and Omicron variants. Notably, two mAbs that amplified in vitro the cytopathic effect of the Delta variant also exhibited neutralization against Omicron. These findings shed light on functional diversity of cross-reactive Abs generated during SARS-CoV-2 infection and illustrate how the balance between neutralizing and enhancing Abs facilitate variant emergence.

Application of Machine Learning Prediction of Individual SARS-CoV-2 Vaccination and Infection Status to the French Serosurveillance Survey From March 2020 to 2022: Cross-Sectional Study.

BACKGROUND: The seroprevalence of SARS-CoV-2 infection in the French population was estimated with a representative, repeated cross-sectional survey based on residual sera from routine blood testing. These data contained no information on infection or vaccination status, thus limiting the ability to detail changes observed in the immunity level of the population over time. OBJECTIVE: Our aim is to predict the infected or vaccinated status of individuals in the French serosurveillance survey based only on the results of serological assays. Reference data on longitudinal serological profiles of seronegative, infected, and vaccinated individuals from another French cohort were used to build the predictive model. METHODS: A model of individual vaccination or infection status with respect to SARS-CoV-2 obtained from a machine learning procedure was proposed based on 3 complementary serological assays. This model was applied to the French nationwide serosurveillance survey from March 2020 to March 2022 to estimate the proportions of the population that were negative, infected, vaccinated, or infected and vaccinated. RESULTS: From February 2021 to March 2022, the estimated percentage of infected and unvaccinated individuals in France increased from 7.5% to 16.8%. During this period, the estimated percentage increased from 3.6% to 45.2% for vaccinated and uninfected individuals and from 2.1% to 29.1% for vaccinated and infected individuals. The decrease in the seronegative population can be largely attributed to vaccination. CONCLUSIONS: Combining results from the serosurveillance survey with more complete data from another longitudinal cohort completes the information retrieved from serosurveillance while keeping its protocol simple and easy to implement.

Estimated protection against COVID-19 based on predicted neutralisation titres from multiple antibody measurements in a longitudinal cohort, France, April 2020 to November 2021.

BackgroundThe risk of SARS-CoV-2 (re-)infection remains present given waning of vaccine-induced and infection-acquired immunity, and ongoing circulation of new variants.AimTo develop a method that predicts virus neutralisation and disease protection based on variant-specific antibody measurements to SARS-CoV-2 antigens.MethodsTo correlate antibody and neutralisation titres, we collected 304 serum samples from individuals with either vaccine-induced or infection-acquired SARS-CoV-2 immunity. Using the association between antibody and neutralisation titres, we developed a prediction model for SARS-CoV-2-specific neutralisation titres. From predicted neutralising titres, we inferred protection estimates to symptomatic and severe COVID-19 using previously described relationships between neutralisation titres and protection estimates. We estimated population immunity in a French longitudinal cohort of 905 individuals followed from April 2020 to November 2021.ResultsWe demonstrated a strong correlation between anti-SARS-CoV-2 antibodies measured using a low cost high-throughput assay and antibody response capacity to neutralise live virus. Participants with a single vaccination or immunity caused by infection were especially vulnerable to symptomatic or severe COVID-19. While the median reduced risk of COVID-19 from Delta variant infection in participants with three vaccinations was 96% (IQR: 94-98), median reduced risk among participants with infection-acquired immunity was only 42% (IQR: 22-66).ConclusionOur results are consistent with data from vaccine effectiveness studies, indicating the robustness of our approach. Our multiplex serological assay can be readily adapted to study new variants and provides a framework for development of an assay that would include protection estimates.

SARS-CoV-2-related bat virus behavior in human-relevant models sheds light on the origin of COVID-19.

Bat sarbecovirus BANAL-236 is highly related to SARS-CoV-2 and infects human cells, albeit lacking the furin cleavage site in its spike protein. BANAL-236 replicates efficiently and pauci-symptomatically in humanized mice and in macaques, where its tropism is enteric, strongly differing from that of SARS-CoV-2. BANAL-236 infection leads to protection against superinfection by a virulent strain. We find no evidence of antibodies recognizing bat sarbecoviruses in populations in close contact with bats in which the virus was identified, indicating that such spillover infections, if they occur, are rare. Six passages in humanized mice or in human intestinal cells, mimicking putative early spillover events, select adaptive mutations without appearance of a furin cleavage site and no change in virulence. Therefore, acquisition of a furin site in the spike protein is likely a pre-spillover event that did not occur upon replication of a SARS-CoV-2-like bat virus in humans or other animals. Other hypotheses regarding the origin of the SARS-CoV-2 should therefore be evaluated, including the presence of sarbecoviruses carrying a spike with a furin cleavage site in bats.

Neutralising antibody responses to SARS-CoV-2 omicron among elderly nursing home residents following a booster dose of BNT162b2 vaccine: A community-based, prospective, longitudinal cohort study.

Background: The protective immunity against omicron following a BNT162b2 Pfizer booster dose among elderly individuals (ie, those aged >65 years) is not well characterised. Methods: In a community-based, prospective, longitudinal cohort study taking place in France in which 75 residents from three nursing homes were enrolled, we selected 38 residents who had received a two-dose regimen of mRNA vaccine and a booster dose of Pfizer BNT162b2 vaccine. We excluded individuals that did not receive three vaccine doses or did not have available sera samples. We measured anti-S IgG antibodies and neutralisation capacity in sera taken 56 (28-68) and 55 (48-64) days (median (range)) after the 2nd and 3rd vaccine doses, respectively. Antibodies targeting the SARS-CoV-2 Spike protein were measured with the S-Flow assay as binding antibody units per milliliter (BAU/mL). Neutralising activities in sera were measured as effective dilution 50% (ED50) with the S-Fuse assay using authentic isolates of delta and omicron BA.1. Findings: Among the 38 elderly individuals recruited to the cohort study between November 23rd, 2020 and April 29th, 2021, with median age of 88 (range 72-101) years, 30 (78.95%) had been previously infected with SARS-CoV-2. After three vaccine doses, serum neutralising activity was lower against omicron BA.1 (median ED50 of 774.5, range 15.0-34660.0) than the delta variant (median ED50 of 4972.0, range 213.7-66340.0), and higher among previously infected (ie, convalescent; median ED50 against omicron: 1088.0, range 32.6-34660.0) compared with infection-naive residents (median ED50 against omicron: 188.4, range 15.0-8918.0). During the French omicron wave in December 2021-January 2022, 75% (6/8) of naive residents were infected, compared to 25% (7/30) of convalescent residents (P=0.0114). Anti-Spike antibody levels and neutralising activity against omicron BA.1 after a third BNT162b2 booster dose were lower in those with breakthrough BA.1 infection (n=13) compared with those without (n=25), with a median of 1429.9 (range 670.9-3818.3) BAU/mL vs 2528.3 (range 695.4-8832.0) BAU/mL (P=0.029) and a median ED50 of 281.1 (range 15.0-2136.0) vs 1376.0 (range 32.6-34660.0) (P=0.0013), respectively. Interpretation: This study shows that elderly individuals who received three vaccine doses elicit neutralising antibodies against the omicron BA.1 variant of SARS-CoV-2. Elderly individuals who had also been previously infected showed higher neutralising activity compared with naive individuals. Yet, breakthrough infections with omicron occurred. Individuals with breakthrough infections had significantly lower neutralising titers compared to individuals without breakthrough infection. Thus, a fourth dose of vaccine may be useful in the elderly population to increase the level of neutralising antibodies and compensate for waning immunity. Funding: Institut Pasteur, Fondation pour la Recherche Médicale (FRM), European Health Emergency Preparedness and Response Authority (HERA), Agence nationale de recherches sur le sida et les hépatites virales - Maladies Infectieuses Emergentes (ANRS-MIE), Agence nationale de la recherche (ANR), Assistance Publique des Hôpitaux de Paris (AP-HP) and Fondation de France.

Locus specific epigenetic modalities of random allelic expression imbalance.

Most autosomal genes are thought to be expressed from both alleles, with some notable exceptions, including imprinted genes and genes showing random monoallelic expression (RME). The extent and nature of RME has been the subject of debate. Here we investigate the expression of several candidate RME genes in F1 hybrid mouse cells before and after differentiation, to define how they become persistently, monoallelically expressed. Clonal monoallelic expression is not present in embryonic stem cells, but we observe high frequencies of monoallelism in neuronal progenitor cells by assessing expression status in more than 200 clones. We uncover unforeseen modes of allelic expression that appear to be gene-specific and epigenetically regulated. This non-canonical allelic regulation has important implications for development and disease, including autosomal dominant disorders and opens up therapeutic perspectives.

Humoral immunity to SARS-CoV-2 and seasonal coronaviruses in children and adults in north-eastern France.

BACKGROUND: Children are underrepresented in the COVID-19 pandemic and often experience milder disease than adolescents and adults. Reduced severity is possibly due to recent and more frequent seasonal human coronaviruses (HCoV) infections. We assessed the seroprevalence of SARS-CoV-2 and seasonal HCoV specific antibodies in a large cohort in north-eastern France. METHODS: In this cross-sectional seroprevalence study, serum samples were collected from children and adults requiring hospital admission for non-COVID-19 between February and August 2020. Antibody responses to SARS-CoV-2 and seasonal HCoV (229E, HKU1, NL63, OC43) were assessed using a bead-based multiplex assay, Luciferase-Linked ImmunoSorbent Assay, and a pseudotype neutralisation assay. FINDINGS: In 2,408 individuals, seroprevalence of SARS-CoV-2-specific antibodies was 7-8% with three different immunoassays. Antibody levels to seasonal HCoV increased substantially up to the age of 10. Antibody responses in SARS-CoV-2 seropositive individuals were lowest in adults 18-30 years. In SARS-CoV-2 seronegative individuals, we observed cross-reactivity between antibodies to the four HCoV and SARS-CoV-2 Spike. In contrast to other antibodies to SARS-CoV-2, specific antibodies to sub-unit 2 of Spike (S2) in seronegative samples were highest in children. Upon infection with SARS-CoV-2, antibody levels to Spike of betacoronavirus OC43 increased across the whole age spectrum. No SARS-CoV-2 seropositive individuals with low levels of antibodies to seasonal HCoV were observed. INTERPRETATION: Our findings underline significant cross-reactivity between antibodies to SARS-CoV-2 and seasonal HCoV, but provide no significant evidence for cross-protective immunity to SARS-CoV-2 infection due to a recent seasonal HCoV infection. In particular, across all age groups we did not observe SARS-CoV-2 infected individuals with low levels of antibodies to seasonal HCoV. FUNDING: This work was supported by the « URGENCE COVID-19 ¼ fundraising campaign of Institut Pasteur, by the French Government's Investissement d'Avenir program, Laboratoire d'Excellence Integrative Biology of Emerging Infectious Diseases (Grant No. ANR-10-LABX-62-IBEID), and by the REACTing (Research & Action Emerging Infectious Diseases), and by the RECOVER project funded by the European Union's Horizon 2020 research and innovation programme under grant agreement No. 101003589, and by a grant from LabEx IBEID (ANR-10-LABX-62-IBEID).

SPEN integrates transcriptional and epigenetic control of X-inactivation.

Xist represents a paradigm for the function of long non-coding RNA in epigenetic regulation, although how it mediates X-chromosome inactivation (XCI) remains largely unexplained. Several proteins that bind to Xist RNA have recently been identified, including the transcriptional repressor SPEN1-3, the loss of which has been associated with deficient XCI at multiple loci2-6. Here we show in mice that SPEN is a key orchestrator of XCI in vivo and we elucidate its mechanism of action. We show that SPEN is essential for initiating gene silencing on the X chromosome in preimplantation mouse embryos and in embryonic stem cells. SPEN is dispensable for maintenance of XCI in neural progenitors, although it significantly decreases the expression of genes that escape XCI. We show that SPEN is immediately recruited to the X chromosome upon the upregulation of Xist, and is targeted to enhancers and promoters of active genes. SPEN rapidly disengages from chromatin upon gene silencing, suggesting that active transcription is required to tether SPEN to chromatin. We define the SPOC domain as a major effector of the gene-silencing function of SPEN, and show that tethering SPOC to Xist RNA is sufficient to mediate gene silencing. We identify the protein partners of SPOC, including NCoR/SMRT, the m6A RNA methylation machinery, the NuRD complex, RNA polymerase II and factors involved in the regulation of transcription initiation and elongation. We propose that SPEN acts as a molecular integrator for the initiation of XCI, bridging Xist RNA with the transcription machinery-as well as with nucleosome remodellers and histone deacetylases-at active enhancers and promoters.

Landscape of monoallelic DNA accessibility in mouse embryonic stem cells and neural progenitor cells.

We developed an allele-specific assay for transposase-accessible chromatin with high-throughput sequencing (ATAC-seq) to genotype and profile active regulatory DNA across the genome. Using a mouse hybrid F1 system, we found that monoallelic DNA accessibility across autosomes was pervasive, developmentally programmed and composed of several patterns. Genetically determined accessibility was enriched at distal enhancers, but random monoallelically accessible (RAMA) elements were enriched at promoters and may act as gatekeepers of monoallelic mRNA expression. Allelic choice at RAMA elements was stable across cell generations and bookmarked through mitosis. RAMA elements in neural progenitor cells were biallelically accessible in embryonic stem cells but premarked with bivalent histone modifications; one allele was silenced during differentiation. Quantitative analysis indicated that allelic choice at the majority of RAMA elements is consistent with a stochastic process; however, up to 30% of RAMA elements may deviate from the expected pattern, suggesting a regulated or counting mechanism.

Structural organization of the inactive X chromosome in the mouse.

X-chromosome inactivation (XCI) involves major reorganization of the X chromosome as it becomes silent and heterochromatic. During female mammalian development, XCI is triggered by upregulation of the non-coding Xist RNA from one of the two X chromosomes. Xist coats the chromosome in cis and induces silencing of almost all genes via its A-repeat region, although some genes (constitutive escapees) avoid silencing in most cell types, and others (facultative escapees) escape XCI only in specific contexts. A role for Xist in organizing the inactive X (Xi) chromosome has been proposed. Recent chromosome conformation capture approaches have revealed global loss of local structure on the Xi chromosome and formation of large mega-domains, separated by a region containing the DXZ4 macrosatellite. However, the molecular architecture of the Xi chromosome, in both the silent and expressed regions,remains unclear. Here we investigate the structure, chromatin accessibility and expression status of the mouse Xi chromosome in highly polymorphic clonal neural progenitors (NPCs) and embryonic stem cells. We demonstrate a crucial role for Xist and the DXZ4-containing boundary in shaping Xi chromosome structure using allele-specific genome-wide chromosome conformation capture (Hi-C) analysis, an assay for transposase-accessible chromatin with high throughput sequencing (ATAC-seq) and RNA sequencing. Deletion of the boundary disrupts mega-domain formation, and induction of Xist RNA initiates formation of the boundary and the loss of DNA accessibility. We also show that in NPCs, the Xi chromosome lacks active/inactive compartments and topologically associating domains (TADs), except around genes that escape XCI. Escapee gene clusters display TAD-like structures and retain DNA accessibility at promoter-proximal and CTCF-binding sites. Furthermore, altered patterns of facultative escape genes indifferent neural progenitor clones are associated with the presence of different TAD-like structures after XCI. These findings suggest a key role for transcription and CTCF in the formation of TADs in the context of the Xi chromosome in neural progenitors.

Live cell imaging of the nascent inactive X chromosome during the early differentiation process of naive ES cells towards epiblast stem cells.

Random X-chromosome inactivation ensures dosage compensation in mammals through the transcriptional silencing of one of the two X chromosomes present in each female cell. Silencing is initiated in the differentiating epiblast of the mouse female embryos through coating of the nascent inactive X chromosome by the non-coding RNA Xist, which subsequently recruits the Polycomb Complex PRC2 leading to histone H3-K27 methylation. Here we examined in mouse ES cells the early steps of the transition from naive ES cells towards epiblast stem cells as a model for inducing X chromosome inactivation in vitro. We show that these conditions efficiently induce random XCI. Importantly, in a transient phase of this differentiation pathway, both X chromosomes are coated with Xist RNA in up to 15% of the XX cells. In an attempt to determine the dynamics of this process, we designed a strategy aimed at visualizing the nascent inactive X-chromosome in live cells. We generated transgenic female XX ES cells expressing the PRC2 component Ezh2 fused to the fluorescent protein Venus. The fluorescent fusion protein was expressed at sub-physiological levels and located in nuclei of ES cells. Upon differentiation of ES cell towards epiblast stem cell fate, Venus-fluorescent territories appearing in interphase nuclei were identified as nascent inactive X chromosomes by their association with Xist RNA. Imaging of Ezh2-Venus for up to 24 hours during the differentiation process showed survival of some cells with two fluorescent domains and a surprising dynamics of the fluorescent territories across cell division and in the course of the differentiation process. Our data reveal a strategy for visualizing the nascent inactive X chromosome and suggests the possibility for a large plasticity of the nascent inactive X chromosome.

Developmental dynamics and disease potential of random monoallelic gene expression.

X chromosome inactivation (XCI) and allelic exclusion of olfactory receptors or immunoglobulin loci represent classic examples of random monoallelic expression (RME). RME of some single copy genes has also been reported, but the in vivo relevance of this remains unclear. Here we identify several hundred RME genes in clonal neural progenitor cell lines derived from embryonic stem cells. RME occurs during differentiation, and, once established, the monoallelic state can be highly stable. We show that monoallelic expression also occurs in vivo, in the absence of DNA sequence polymorphism. Several of the RME genes identified play important roles in development and have been implicated in human autosomal-dominant disorders. We propose that monoallelic expression of such genes contributes to the fine-tuning of the developmental regulatory pathways they control, and, in the context of a mutation, RME can predispose to loss of function in a proportion of cells and thus contribute to disease.

Nucleosome assembly proteins and their interacting proteins in neuronal differentiation.

Neuronal differentiation from neural stem cells into mature neurons is guided by the concerted action of specific transcription factors that stepwise exercise their role in the context of defined chromatin states. Amongst the classes of proteins that influence chromatin compaction and modification are nucleosome assembly proteins (NAPs). Mammals possess several nucleosome assembly protein 1 like proteins (NAP1L) that show either ubiquitous or neuron-restricted expression. The latter group is presumably involved in the process of neuronal differentiation. Mammalian NAP1Ls can potentially form both homo- and hetero-dimers and octamers, in theory allowing thousands of different combinations to be formed. Detailed studies have been performed on several of the NAP1Ls that point to a range of molecular roles, including transcriptional regulation, nuclear import, and control of cell division. This article aims at summarizing current knowledge of the mammalian NAP1L family and its interactions.

Interaction between nucleosome assembly protein 1-like family members.

Mammals possess five nucleosome assembly protein 1-like (NAP1L) proteins, with three of them being expressed exclusively in the nervous system. The biological importance of the neuron-specific NAP1L2 protein is demonstrated by the neural tube defects occurring during the embryonic development of Nap1l2 mutant mice, which are associated with an overproliferation of neural stem cells and decreased neuronal differentiation. NAP1L2 controls the expression of its target genes, such as the cell cycle regulator Cdkn1c, at least in part via an effect on histone acetylation. Using a two-hybrid analysis, we have identified several proteins interacting with NAP1L2, including the ubiquitously expressed members of the nucleosome assembly protein family, NAP1L1 and NAP1L4. Structural studies further predict that all five NAP1-like proteins are able to interact directly via their highly conserved α-helices. These elements, in conjunction with the coexpression of all the NAP1-like proteins in neurons and the finding that deletion of Nap1l2 affects the cytoplasmic-nuclear distribution patterns of both NAP1L1 and NAP1L4 and their recruitment to target genes, suggest that combinatorial variation within the NAP family may ensure adaptation to the specific requirements for neuronal differentiation such as intercellular repartition, chromatin modification, transcriptional regulation, or the recruitment of specific transcription factors.

Molecular coupling of Tsix regulation and pluripotency.

The reprogramming of X-chromosome inactivation during the acquisition of pluripotency in vivo and in vitro is accompanied by the repression of Xist, the trigger of X-inactivation, and the upregulation of its antisense counterpart Tsix. We have shown that key factors supporting pluripotency-Nanog, Oct4 and Sox2-bind within Xist intron 1 in undifferentiated embryonic stem cells (ESC) to repress Xist transcription. However, the relationship between transcription factors of the pluripotency network and Tsix regulation has remained unclear. Here we show that Tsix upregulation in embryonic stem cells depends on the recruitment of the pluripotent marker Rex1, and of the reprogramming-associated factors Klf4 and c-Myc, by the DXPas34 minisatellite associated with the Tsix promoter. Upon deletion of DXPas34, binding of the three factors is abrogated and the transcriptional machinery is no longer efficiently recruited to the Tsix promoter. Additional analyses including knockdown experiments further demonstrate that Rex1 is critically important for efficient transcription elongation of Tsix. Hence, distinct embryonic-stem-cell-specific complexes couple X-inactivation reprogramming and pluripotency, with Nanog, Oct4 and Sox2 repressing Xist to facilitate the reactivation of the inactive X, and Klf4, c-Myc and Rex1 activating Tsix to remodel Xist chromatin and ensure random X-inactivation upon differentiation. The holistic pattern of Xist/Tsix regulation by pluripotent factors that we have identified suggests a general direct governance of complex epigenetic processes by the machinery dedicated to pluripotency.

Nap1l2 promotes histone acetylation activity during neuronal differentiation.

The deletion of the neuronal Nap1l2 (nucleosome assembly protein 1-like 2) gene in mice causes neural tube defects. We demonstrate here that this phenotype correlates with deficiencies in differentiation and increased maintenance of the neural stem cell stage. Nap1l2 associates with chromatin and interacts with histones H3 and H4. Loss of Nap1l2 results in decreased histone acetylation activity, leading to transcriptional changes in differentiating neurons, which include the marked downregulation of the Cdkn1c (cyclin-dependent kinase inhibitor 1c) gene. Cdkn1c expression normally increases during neuronal differentiation, and this correlates with the specific recruitment of the Nap1l2 protein and an increase in acetylated histone H3K9/14 at the site of Cdkn1c transcription. These results lead us to suggest that the Nap1l2 protein plays an important role in regulating transcription in developing neurons via the control of histone acetylation. Our data support the idea that neuronal nucleosome assembly proteins mediate cell-type-specific mechanisms of establishment/modification of a chromatin-permissive state that can affect neurogenesis and neuronal survival.