The cerebral cortex develops through the coordinated generation of dozens of neuronal subtypes, but the mechanisms involved remain unclear. Here we show that mouse embryonic stem cells, cultured without any morphogen but in the presence of a sonic hedgehog inhibitor, recapitulate in vitro the major milestones of cortical development, leading to the sequential generation of a diverse repertoire of neurons that display most salient features of genuine cortical pyramidal neurons. When grafted into the cerebral cortex, these neurons develop patterns of axonal projections corresponding to a wide range of cortical layers, but also to highly specific cortical areas, in particular visual and limbic areas, thereby demonstrating that the identity of a cortical area can be specified without any influence from the brain. The discovery of intrinsic corticogenesis sheds new light on the mechanisms of neuronal specification, and opens new avenues for the modelling and treatment of brain diseases. In a further attempt to prove the validity of this model, we have initiated the study of the mechanism of action of FoxG1, a forkhead box transcription factor involved in the control of cell fate decision in the developing cortex.

Le cortex cérébral constitue l’une des structures les plus évoluées et complexes de notre cerveau. Sa surface est divisée en de nombreuses aires fonctionnelles. La mise en place des aires corticales dépend à la fois de facteurs intrinsèques comme la sécrétion de morphogènes ou l’expression en gradient de différents facteurs de transcription, mais elle dépend aussi de facteurs extrinsèques au cortex, en particulier l'innervation par le thalamus. Les ephrines et leurs récepteurs Eph constituent une famille multigénique de facteurs de signalisation impliqués dans divers événements clé du développement cortical où ils sont exprimés selon des profils spatio-temporels complexes. Aux stades tardifs du développement, EphA7 et l’ephrine-A5 sont exprimés en gradients complémentaires au sein de chaque territoire des aires présomptives, constituant ainsi les marqueurs les plus précoces de ces aires corticales. Par la combinaison d’approches in-vitro utilisant la technique d’électroporation focale de tranches corticales embryonnaires, puis in-vivo en utilisant la technique de transgénèse d’addition, nous avons identifié une séquence régulatrice de EphA7 appelée pA7, capable de mimer l’expression endogène de EphA7 au sein du télencéphale dorsal en développement. La lignée de souris pA7-GFP ainsi générée exprime la GFP spécifiquement au sein du télencéphale dorsal durant les stades précoces. Aux stades périnataux cette expression se régionalise au sein de la plaque corticale de chacune des aires présomptives selon des gradients récapitulant ceux observés pour EphA7. Nous avons ensuite purifié des neurones exprimant différents niveaux d’EphA7 par la technique de FACS «Fluorescence-Activated Cell Sorting » et l’analyse de leur transcriptome nous a permis de trouver un grand nombre de gènes différentiellement exprimés. Tous ceux testés par la technique d’hybridation in situ sont exprimés selon un gradient latéral fort et médial faible dans le cortex pariétal, similaire à celui d’EphA7. L’examination de leur profil au sein de cortex de souris dépourvus d’afférences thalamiques, nous a permis de conclure que l’expression de ces gènes incluant EphA7 s’établit indépendamment de celles-ci. Ainsi, notre étude a permis d'identifier un répertoire de gènes neuronaux, pouvant agir en amont ou en combinaison avec EphA7 pour contrôler les facteurs intrinsèques essentiels à l’établissement des aires corticales./ The cerebral cortex is subdivided into distinct cortical areas characterized by specific patterns of gene expression and neuronal connectivity. The patterning of cortical areas is thought to be controlled by a combination of intrinsic factors that are expressed in the cortex, and external signals such as inputs from the thalamus. EphA7 is a member of the ephrin/Eph family of guidance factors that is involved in key aspects of the development of the cortex, and is expressed in several gradients within developing cortical areas. By combining in vitro transcriptional assays and mouse transgenics, we identified a regulatory element of the EphA7 promoter, named pA7, that can recapitulate salient features of the pattern of expression of EphA7 in the developing forebrain, including gradients in the cortex. Using a mouse reporter line where GFP expression recapitulates EphA7 expression, we developed a GFP-based cell sorting procedure to isolate cortical neuron populations displaying different levels of EphA7 expression. Transcriptome analysis of these populations enabled to identify a specific array of differentially expressed genes. All genes validated further in vivo were confirmed to be expressed along distinct gradients in the developing cortical plate, similarly to EphA7. The expression of these genes was unchanged in mutant mice defective for thalamocortical projections, indicating that their graded pattern is largely intrinsic to the cortex. Our study identifies a novel repertoire of cortical neuron genes that may act upstream of, or together with EphA7, to control the intrinsic patterning of cortical areas.

Most of the extant humor research has focused on humor comprehension with only a few studies investigating humor appreciation as a separate construct. The purpose of this investigation was to determine the relation between humor and underlying cognitive processes. Literature on brain injured individuals has indicated that working memory, verbal and visual-spatial reasoning, cognitive flexibility, and concept formation are related to performance on comprehension tests of humor. In this study, cognitive processes underlying both verbal and nonverbal humor were investigated in a sample of healthy young adults. There is evidence that semantic and phonological humor are associated with different neural networks; therefore, both semantic and phonological humor were explored. Studies investigating physiological arousal and humor have indicated that arousal is necessary for the experience of humor. This suggests that the appreciation of humor may require the integration of cognitive and affective information, a process mediated by the ventromedial prefrontal cortex (VMPFC). Thus, a second goal of this study was to investigate the relationship between humor comprehension and appreciation and the VMPFC, by including experimental tasks that previously have been linked to VMPFC functioning. Participants included 94 undergraduate psychology students between the ages of 18 and 39 years. Participants watched film clips and listened to jokes. After the presentation of each joke and each film clip, they completed a humor comprehension/appreciation inventory developed for this study. They also completed measures assessing a range of cognitive abilities hypothesized to underlie humor perception. Hierarchical regression analyses revealed that verbal reasoning was predictive of semantic humor comprehension, indicating that verbal reasoning is a core cognitive ability for the comprehension of jokes in which the humor depends on factors other than simple word play. Cognitive measures were not predictive of phonological humor comprehension or nonverbal humor comprehension. Hierarchical regression analyses revealed that the indicators of VMPFC functioning did not correlate with either humor comprehension or humor appreciation and did not moderate the relation between humor comprehension and humor appreciation. Future research is necessary to elucidate the relationships between cognitive abilities and humor perception and to further explore the contribution of the VMPFC to humor appreciation.

In the human adrenal cortex, adrenocorticotropin (ACTH) activates steroid hormone biosynthesis by acutely increasing cholesterol delivery to the mitochondria and chronically up-regulating the transcription of steroidogenic genes (including CYP17). Sphingolipids are a diverse family of phospholipids and glycolipids that mediate a wide variety of cellular processes, including apoptosis, proliferation, and survival. Sterol regulatory element binding proteins (SREBPs) are a family of transcription factors that regulate genes that are involved in cholesterol biosynthesis and fatty acid metabolism. In this study, we investigated the role of sphingolipids in ACTH-dependent steroidogenesis. H295R human adrenocortical cells were treated with ACTH or dibutyryl cAMP (Bt2cAMP) for various time periods and the content of several sphingolipid species was quantified by mass spectrometry. Both ACTH and Bt2cAMP decreased cellular amounts of sphingomyelin, ceramides, sphingosine (So) and sphingosine-1-phosphate (S1P). However, both ACTH and Bt2cAMP increased the activity of sphingosine kinase and the amounts of S1P released into the media. Both So and S1P increased CYP17 mRNA expression and increased cortisol biosynthesis. This increase in CYP17 transcription occurs by promoting SREBP binding to an SRE at -450/-436 basepairs upstream of the transcription initiation site. Furthermore, chromatin immunoprecipitation (ChIP) assays revealed that Bt2cAMP and S1P treatment results in an increase in acetylation of histone H3 and SREBP1 binding to CYP17 promoter. Additionally, transient transfection studies using wild type or mutated hCYP17 promoters and RNA interference (RNAi) assays confirmed the role of SREBP1 in mediating the stimulatory effect of S1P on CYP17 transcription. In summary, our studies demonstrate a link between sphingolipid metabolism and ACTH-dependent steroidogenesis which requires the activation of SREBP1 in human adrenal cortex.

The present study was conducted to determine the effect of differential endogenous estrogen exposure in rats on stress-induced changes in spatial working memory. Subjects comprised male (n=8) and female (n=10) Sprague-Dawley rats, which were trained to complete a T maze, delayed alternation task. Performance was scored as a percentage of trials during which the correct maze arm was selected. Subjects scores were recorded after 1 and 2 hours of restraint stress, as well as after 1 hour of unimpeded movement in a cage placed in the testing room. Restraint stress was effected through physical confinement within plastic, cylindrical tubing. Female subjects underwent each of the testing conditions twice, during periods of high and low endogenous estrogen exposure, as ascertained by microscopic examination of vaginal epithelial cells for estrous cycle stage determination. Females in proestrus (elevated endogenous estrogen exposure) subjected to 1 hour of restraint performed significantly worse than their baseline scores (p=0.0017) or females in estrus (low endogenous estrogen exposure) after 1 hour of restraint (p=0.00014). After 1 hour of restraint, females in proestrus also committed an increased rate of perseverative errors compared to females in estrus, although this increase did not achieve statistical significance (p=0.06). No appreciable differences existed among subject groups in baseline performance or subsequent to 2 hours of restraint stress. Resultant data indicate impaired working memory among female rats under conditions of stress in the context of elevated endogenous estrogen exposure. This study, then, suggests a potential synergistic effect of stress and estrogen in compromising prefrontal cortex function and, therefore, may lend insight into the observed sex-related disparity in the incidence of major depressive disorder and other anxiety-related mood disorders.

Thesis (Ph. D.)--Cornell University, January, 2007. / Vita. Includes bibliographical references (leaves 214-229).

Reproduction de : Thèse de doctorat : Sciences cognitives. Neurosciences : Lyon 2 : 2007. / Bibliogr.

Thèse doctorat : Neurosciences : Strasbourg 1 : 2006. / Titre provenant de l'écran-titre. Bibliogr. 31 p.

Thesis (Ph. D. in Physics)--Vanderbilt University, Dec. 2007. / Title from title screen. Includes bibliographical references.

Dissertation (Ph.D.)--University of Toledo, 2009. / "Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Biomedical Sciences." Title from title page of PDF document. Table of contents (p. iv) gives incorrect starting page numbers for "Bibliography" and "Abstract". "Bibliography" starts on p. 120 (not p. 119); "Abstract" starts on p. 150. Bibliography: p. 64-70, 97-100, 120-149.