S2 – The role of epigenetic mechanisms in typical and stressed developmental trajectories

The symposium will focus on the intricate ways in which neural development is influenced by various factors, including epigenetic mechanisms related to early life adversities and sex-specific differences. The research presented will highlight the importance of intercellular communication in proper trigeminal ganglion formation, with a particular emphasis on the role of microRNA-203 and neural crest-placode interactions. Additionally, the symposium will delve into how methylation/demethylation machinery associates with sex differences during critical periods of development, which may underlie disparities in neural function. Furthermore, studies on the effects of perinatal protein malnutrition and social and material deprivation on brain development and behavioral outcomes will be discussed. These investigations reveal the significant impact of early life experiences on brain structure, function, and behavior, shedding light on the molecular mechanisms that underlie long-lasting effects on mental health. Overall, these results in the field of neural development and epigenetic regulation provide new insights into the complex interplay between genetics, environment, and behavior.

While interactions between neural crest and placode cells are critical for the proper formation of the trigeminal ganglion, the mechanisms underlying this process remain largely uncharacterized. In our study, we show that the microRNA-(miR)203, whose epigenetic repression is required for neural crest migration, is reactivated in coalescing and condensing trigeminal ganglion cells. Overexpression of miR-203 induces ectopic coalescence of neural crest cells and increases ganglion size. Reciprocally, loss of miR-203 function in placode, but not neural crest, cells perturb trigeminal ganglion condensation. Demonstrating intercellular communication, overexpression of miR-203 in the neural crest in vitro or in vivo represses a miR-responsive sensor in placode cells. Moreover, neural crest-secreted extracellular vesicles (EVs), visualized using pHluorin-CD63 vector, become incorporated into the cytoplasm of placode cells. Finally, RT-PCR analysis shows that small EVs isolated from condensing trigeminal ganglia are selectively loaded with miR-203. Together, our findings reveal a critical role in vivo for neural crest-placode communication mediated by small EVs and their selective microRNA cargo for proper trigeminal ganglion formation.

Pablo H. Strobl Mazzulla
Laboratory of Developmental Biology
Instituto Tecnológico de Chascomús (INTECH), CONICET – UNSAM.
Chascomús, Argentina.
www.intech.conicet.gov.ar

In mammals, neural sex differences have been extensively studied offering insight into the neural underpinnings of sex differences in behavior and vulnerabilities to neuropsychiatric disorders. Differences in stable patterns of gene expression in neurons, which determine the neurochemical cell phenotype could underlie differences in neural function, connectivity and neurotransmitter production in males and females. However, the mechanisms underlying sexual differentiation of cell phenotype remain understudied. Recent evidence points to epigenetic modifications occurring early in life as mediators of the organizational effects of testosterone or estradiol during a perinatal critical period. We have found that expression of the epigenetic factors/enzymes involved in DNA methylation and demethylation is greatest during the first week of life. Sex differences in expression of the epigenetic machinery are brain region-specific and a transient inhibition of DNA methylation or demethylation in neonatal male and female mice abolishes several sex differences in cell phenotype in the mouse hypothalamus suggesting that both DNA methylation and demethylation contribute to the development of neural sex differences. Taken together these findings highlight the role of epigenetics as early programing mechanisms mediating sexual differentiation of the brain.

Carla Cisternas
ccisternas@immf.uncor.edu
Instituto de Investigación Médica M. y M. Ferreyra INIMEC, CONICET – UNC, Facultad de Ciencias Exactas Físicas y Naturales, Universidad Nacional de Córdoba – Córdoba, Argentina.
http://www.institutoferreyra.org

Brain development trajectory is altered by early life adversities during critical periods. Mental health is affected in a sex-specific manner, increasing the risk to suffer emotional disorders. We developed a mouse model of perinatal protein malnutrition in which dams were fed with normal (NP) or low (LP) protein diet during gestation and lactation. We observed sex-specific changes associated with memory, social cognition and emotive disorders. Transcriptional deregulation was observed in the immediate early genes and neurotransmission related molecules affecting excitatory/inhibitory balance. In order to understand the mechanisms underlying these changes we evaluate the expression of molecular machinery related with DNA methylation and demethylation, histone acetylation and deacetylation, histones methylation and demethylation and miRNAs. Sex- and region- specific changes on DNA methylation/demethylation machinery, genes encoding enzymes related with H3K27me3 and several miRNAs were found. Our results suggest that epigenetic mechanisms might be involved in the long-lasting effects of perinatal protein malnutrition in mental health.

Mariela Chertoff
marielachertoff@gmail.com
Laboratorio de Neuroepigenética y Adversidades Tempranas – DQB, FCEyN, UBA – IQUIBICEN, CONICET – Buenos Aires, Argentina
www.iquibicen.fcen.uba.ar

Early-life adversities (ELA), such as child low socioeconomic conditions, affect the structure and function of the brain leading to impaired health and psychological well-being later in life. With the aim of understanding the neurobiological sequelae and mechanisms of risk of ELA, we designed and validated a multifactorial murine model of social and material deprivation (SMD) produced by a set of adverse environmental factors assumed to be the proximal factors of low socioeconomic status. Dams exposed to SMD displayed depression-like traits and offered less care to their pups than control dams. Regarding offspring, SMD treated mice presented a neurodevelopmental delay, a dominant behavior, and impaired social cognition. Moreover, SMD males showed signs of aggressiveness. The neural correlates of these behaviors are constituted by morphological changes in the medial prefrontal cortex (mPFC), the amygdala and the hippocampus. Thus, we analyzed global gene expression through RNA-seq in the mPFC from SMD and control offspring. We observed that factors of epigenetic machinery, particularly related to histone methylation/demethylation, were dysregulated in SMD mice in a sex-specific manner. Gene expression alterations in the mPFC provide a molecular mechanism for understanding the neurobiology of exposure to early multidimensional adverse conditions.

Bruno G. Berardino
Laboratorio de Neuroepigenética y Adversidades Tempranas – DQB, FCEyN, UBA – IQUIBICEN, CONICET – Buenos Aires, Argentina
www.iquibicen.fcen.uba.ar