Estrogen receptor alpha is required in GABAergic, but not glutamatergic, neurons to masculinize the brain.

Abstract Masculinization of the rodent brain is driven by estrogen signaling during a perinatal critical period. Genetic deletion of estrogen receptor alpha ( Esr1/ ERα) results in altered hypothalamic-pituitary-gonadal (HPG) axis signaling and a dramatic reduction of male sexual and territorial behaviors. However, the requirement of ERα function in masculinizing distinct classes of neurons, and if these populations mediate components of male-typical behavior, remains unexplored. We deleted ERα in excitatory or inhibitory neurons using either a Vglut2 or Vgat driver and assessed male behaviors. We find that Vglut2 -Cre; Esr1 lox/lox mutant males lack ERa in the ventrolateral region of the ventromedial hypothalamus (VMHvl) and posterior ventral portion of the medial amygdala (MePV). These mutants recapitulate the increased serum testosterone levels seen with constitutive ERα deletion, but have none of the behavioral deficits. In contrast, Vgat -Cre; Esr1 lox/lox males with substantial ERα deletion in inhibitory neurons, including those of the principal nucleus of the bed nucleus of the stria terminalis (BNSTpr), posterior dorsal MeA (MePD), and medial preoptic area (MPOA) have normal testosterone levels, but display alterations in mating and territorial behaviors. These mutants also show demasculinized expression of androgen receptor (AR) and estrogen receptor beta (Esr2). Our results demonstrate that ERα masculinizes GABAergic neurons that gate the display of male-typical behaviors

Notch-Dependent Pituitary SOX2(+) Stem Cells Exhibit a Timed Functional Extinction in Regulation of the Postnatal Gland.

Although SOX2(+) stem cells are present in the postnatal pituitary gland, how they are regulated molecularly and whether they are required for pituitary functions remain unresolved questions. Using a conditional knockout animal model, here we demonstrate that ablation of the canonical Notch signaling in the embryonic pituitary gland leads to progressive depletion of the SOX2(+) stem cells and hypoplastic gland. Furthermore, we show that the SOX2(+) stem cells initially play a significant role in contributing to postnatal pituitary gland expansion by self-renewal and differentiating into distinct lineages in the immediate postnatal period. However, we found that within several weeks postpartum, the SOX2(+) stem cells switch to an essentially dormant state and are no longer required for homeostasis/tissue adaptation. Our results present a dynamic tissue homeostatic model in which stem cells provide an initial contribution to the growth of the neonatal pituitary gland, whereas the mature gland can be maintained in a stem cell-independent fashion

Epithelial Cell Integrin Β1 is Required for Developmental Angiogenesis in the Pituitary Gland

As a key component of the vertebrate neuroendocrine system, the pituitary gland relies on the progressive and coordinated development of distinct hormone-producing cell types and an invading vascular network. The molecular mechanisms that drive formation of the pituitary vasculature, which is necessary for regulated synthesis and secretion of hormones that maintain homeostasis, metabolism, and endocrine function, remain poorly understood. Here, we report that expression of integrin β1 in embryonic pituitary epithelial cells is required for angiogenesis in the developing mouse pituitary gland. Deletion of pituitary epithelial integrin β1 before the onset of angiogenesis resulted in failure of invading endothelial cells to recruit pericytes efficiently, whereas deletion later in embryogenesis led to decreased vascular density and lumen formation. In both cases, lack of epithelial integrin β1 was associated with a complete absence of vasculature in the pituitary gland at birth. Within pituitary epithelial cells, integrin β1 directs a large transcriptional program that includes components of the extracellular matrix and associated signaling factors that are linked to the observed non–cell-autonomous effects on angiogenesis. We conclude that epithelial integrin β1 functions as a critical and canonical regulator of developmental angiogenesis in the pituitary gland, thus providing insight into the long-standing systems biology conundrum of how vascular invasion is coordinated with tissue development

Epigenetic Mechanisms of Brain Sexual Differentiation

Across vertebrate species, gonadal hormones coordinate physiology with behavior to facilitate social interactions essential for reproduction and survival. In adulthood, these hormones activate neural circuits that regulate behaviors presenting differently in females and males, such as parenting and territorial aggression. Yet long before sex-typical behaviors emerge at puberty, transient hormone production during sensitive periods of neurodevelopment establish the circuits upon which adult hormones act. How transitory waves of early-life hormone signaling exert lasting effects on the brain remains a central question. Here we discuss how perinatal estradiol signaling organizes cellular and molecular sex differences in the rodent brain. We review classic anatomic studies revealing sex differences in cell number, volume, and neuronal projections, and consider how single-cell sequencing methods enable distinction between sex-biased cell-type abundance and gene expression. Finally, we highlight the recent discovery of a gene regulatory program activated by estrogen receptor α (ERα) following the perinatal hormone surge. A subset of this program displays sustained sex-biased gene expression and chromatin accessibility throughout the postnatal sensitive period, demonstrating a bona fide epigenetic mechanism. We propose that ERα-expressing neurons throughout the social behavior network use similar gene regulatory programs to coordinate brain sexual differentiation

Estrogen receptor alpha is required in GABAergic, but not glutamatergic, neurons to masculinize behavior

Masculinization of the altricial rodent brain is driven by estrogen signaling during a perinatal critical period. Genetic deletion of estrogen receptor alpha (Esr1/ERα) results in altered hypothalamic-pituitary-gonadal (HPG) axis signaling and a dramatic reduction of male sexual and territorial behaviors. However, the role of ERα in masculinizing distinct classes of neurons remains unexplored. We deleted ERα in excitatory or inhibitory neurons using either a Vglut2 or Vgat driver and assessed male behaviors. We find that Vglut2-Cre;Esr1lox/lox mutant males lack ERα in the ventrolateral region of the ventromedial hypothalamus (VMHvl) and posterior ventral portion of the medial amygdala (MePV). These mutants recapitulate the increased serum testosterone levels seen with constitutive ERα deletion, but have none of the behavioral deficits. In contrast, Vgat-Cre;Esr1lox/lox males with substantial ERα deletion in inhibitory neurons, including those of the principal nucleus of the bed nucleus of the stria terminalis (BNSTpr), posterior dorsal MeA (MePD), and medial preoptic area (MPOA) have normal testosterone levels, but display alterations in mating and territorial behaviors. These mutants also show dysmasculinized expression of androgen receptor (AR) and estrogen receptor beta (Esr2). Our results demonstrate that ERα masculinizes GABAergic neurons that gate the display of male-typical behaviors

Specificity in sociogenomics: Identifying causal relationships between genes and behavior.

There has been rapid growth in the use of transcriptomic analyses to study the interplay between gene expression and behavior. Experience can modify gene expression in the brain, leading to changes in internal state and behavioral displays, while gene expression variation between species is thought to specify many innate behavior differences. However, providing a causal association between a gene and a given behavior remains challenging as it is difficult to determine when and where a gene contributes to the function of a behaviorally-relevant neuronal population. Moreover, given that there are fewer genetic tools available for non-traditional model organisms, transcriptomic approaches have been largely limited to profiling of bulk tissue, which can obscure the contributions of subcortical brain regions implicated in multiple behaviors. Here, we discuss how emerging single cell technologies combined with methods offering additional spatial and connectivity information can give us insight about the genetic profile of specific cells involved in the neural circuit of target social behaviors. We also emphasize how these techniques are broadly adaptable to non-traditional model organisms. We propose that, ultimately, a combination of these approaches applied throughout development will be key to discerning how genes shape the formation of social behavior circuits

Notch-Dependent Pituitary SOX2(+) Stem Cells Exhibit a Timed Functional Extinction in Regulation of the Postnatal Gland.

Although SOX2(+) stem cells are present in the postnatal pituitary gland, how they are regulated molecularly and whether they are required for pituitary functions remain unresolved questions. Using a conditional knockout animal model, here we demonstrate that ablation of the canonical Notch signaling in the embryonic pituitary gland leads to progressive depletion of the SOX2(+) stem cells and hypoplastic gland. Furthermore, we show that the SOX2(+) stem cells initially play a significant role in contributing to postnatal pituitary gland expansion by self-renewal and differentiating into distinct lineages in the immediate postnatal period. However, we found that within several weeks postpartum, the SOX2(+) stem cells switch to an essentially dormant state and are no longer required for homeostasis/tissue adaptation. Our results present a dynamic tissue homeostatic model in which stem cells provide an initial contribution to the growth of the neonatal pituitary gland, whereas the mature gland can be maintained in a stem cell-independent fashion