Growth factors synthesized by ovarian somatic cells directly affect oocyte growth and function, but it is unclear whether oocyte-secreted factors play a reciprocal role in modulating somatic cell functions in vivo. During the functional analysis of members of the transforming growth factor-beta superfamily in mouse development, we have uncovered a new family member, growth differentiation factor-9 (GDF-9), which is required for ovarian folliculogenesis. GDF-9 messenger RNA is synthesized only in the oocyte from the primary one-layer follicle stage until after ovulation. Here we analyse ovaries from GDF-9-deficient female mice and demonstrate that primordial and primary one-layer follicles can be formed, but there is a block in follicular development beyond the primary one-layer follicle stage which leads to complete infertility. Oocyte growth and zona pellucida formation proceed normally, but other aspects of oocyte differentiation are compromised. Thus, GDF-9 is the first oocyte-derived growth factor required for somatic cell function in vivo.

The adult stem cell marker Lgr5 and its relative Lgr4 are often co-expressed in Wnt-driven proliferative compartments. We find that conditional deletion of both genes in the mouse gut impairs Wnt target gene expression and results in the rapid demise of intestinal crypts, thus phenocopying Wnt pathway inhibition. Mass spectrometry demonstrates that Lgr4 and Lgr5 associate with the Frizzled/Lrp Wnt receptor complex. Each of the four R-spondins, secreted Wnt pathway agonists, can bind to Lgr4, -5 and -6. In HEK293 cells, RSPO1 enhances canonical WNT signals initiated by WNT3A. Removal of LGR4 does not affect WNT3A signalling, but abrogates the RSPO1-mediated signal enhancement, a phenomenon rescued by re-expression of LGR4, -5 or -6. Genetic deletion of Lgr4/5 in mouse intestinal crypt cultures phenocopies withdrawal of Rspo1 and can be rescued by Wnt pathway activation. Lgr5 homologues are facultative Wnt receptor components that mediate Wnt signal enhancement by soluble R-spondin proteins. These results will guide future studies towards the application of R-spondins for regenerative purposes of tissues expressing Lgr5 homologues.

The oxytocin receptor (OXTR) and its ligand, oxytocin (OXT), regulate reproductive physiology (i.e., parturition and lactation) and sociosexual behaviors. To define the essential functions of OXTR, we generated mice with a null mutation in the Oxtr gene (Oxtr ؊/؊ ) and compared them with OXT-deficient (Oxt ؊/؊ ) mice. Oxtr ؊/؊ mice were viable and had no obvious deficits in fertility or reproductive behavior. Oxtr ؊/؊ dams exhibited normal parturition but demonstrated defects in lactation and maternal nurturing. Infant Oxtr ؊/؊ males emitted fewer ultrasonic vocalizations than wild-type littermates in response to social isolation. Adult Oxtr ؊/؊ males also showed deficits in social discrimination and elevated aggressive behavior. Ligand Oxt ؊/؊ males from Oxt ؊/؊ dams, but not from Oxt ؉/؊ dams, showed similar high levels of aggression. These data suggest a developmental role for the OXT͞OXTR system in shaping adult aggressive behavior. Our studies demonstrate that OXTR plays a critical role in regulating several aspects of social behavior and may have important implications for developmental psychiatric disorders characterized by deficits in social behavior.lactation ͉ maternal behavior ͉ ultrasonic vocalization ͉ social discrimination ͉ aggressive behavior

The oxytocin receptor has been implicated in the regulation of reproductive physiology as well as social and emotional behaviors. The neurochemical mechanisms by which oxytocin receptor modulates social and emotional behavior remains elusive, in part because of a lack of sensitive and selective antibodies for cellular localization. To more precisely characterize oxytocin receptor-expressing neurons within the brain, we generated an oxytocin receptor-reporter mouse in which part of the oxytocin receptor gene was replaced with Venus cDNA (a variant of yellow fluorescent protein). Examination of the Venus expression revealed that, in the raphe nuclei, about one-half of tryptophan hydroxylase-immunoreactive neurons were positive for Venus, suggesting a potential role for oxytocin in the modulation of serotonin release. Oxytocin infusion facilitated serotonin release within the median raphe nucleus and reduced anxiety-related behavior. Infusion of a 5-HT 2A/2C receptor antagonist blocked the anxiolytic effect of oxytocin, suggesting that oxytocin receptor activation in serotonergic neurons mediates the anxiolytic effects of oxytocin. This is the first demonstration that oxytocin may regulate serotonin release and exert anxiolytic effects via direct activation of oxytocin receptor expressed in serotonergic neurons of the raphe nuclei. These results also have important implications for psychiatric disorders such as autism and depression in which both the oxytocin and serotonin systems have been implicated.

Oxytocin, a neurohypophyseal hormone, has been traditionally considered essential for mammalian reproduction. In addition to uterine contractions during labor and milk ejection during nursing, oxytocin has been implicated in anterior pituitary function, paracrine effects in the testis and ovary, and the neural control of maternal and sexual behaviors. To determine the essential role(s) of oxytocin in mammalian reproductive function, mice deficient in oxytocin have been generated using embryonic stem cell technology. A deletion of exon 1 encoding the oxytocin peptide was generated in embryonic stem cells at a high frequency and was successfully transmitted in the germ line. Southern blot analysis of genomic DNA from homozygote offspring and in situ hybridization with an exonic probe 3' of the deletion failed to detect any oxytocin or neurophysin sequences, respectively, confirming that the mutation was a null mutation.

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We report that oxytocin (OT), a primitive neurohypophyseal hormone, hitherto thought solely to modulate lactation and social bonding, is a direct regulator of bone mass. Deletion of OT or the OT receptor (Oxtr) in male or female mice causes osteoporosis resulting from reduced bone formation. Consistent with low bone formation, OT stimulates the differentiation of osteoblasts to a mineralizing phenotype by causing the up-regulation of BMP-2, which in turn controls Schnurri-2 and 3, Osterix, and ATF-4 expression. In contrast, OT has dual effects on the osteoclast. It stimulates osteoclast formation both directly, by activating NF-B and MAP kinase signaling, and indirectly through the up-regulation of RANK-L. On the other hand, OT inhibits bone resorption by mature osteoclasts by triggering cytosolic Ca 2؉ release and NO synthesis. Together, the complementary genetic and pharmacologic approaches reveal OT as a novel anabolic regulator of bone mass, with potential implications for osteoporosis therapy.osteoblast ͉ osteoclast ͉ osteoporosis ͉ pituitary hormones ͉ bone density O xytocin (OT), a hypothalamic nanopeptide secreted into the circulation from the posterior pituitary, is indispensable for lactation. It acts on a G protein-coupled receptor (Oxtr), the expression of which in reproductive tissues is regulated by sex steroids and OT. In humans and rodents, plasma OT levels are elevated maximally during suckling (1, 2).Mice lacking OT or its receptor (Oxtr) are unable to lactate, despite unperturbed breast tissue and milk formation (3, 4). Most notably, newborn pups die shortly after birth in the absence of a foster mother postpartum. This effect of OT is exerted peripherally, as the i.p. administration of recombinant OT to OT Ϫ/Ϫ mice rescues milk ejection, allowing the newborn to feed normally. In contrast to the milk ejection defect, no deficits in copulation, gestation, fecundity, or parturition have been noted in either OT Ϫ/Ϫ or Oxtr Ϫ/Ϫ mice, suggesting that these mice are typically eugonadal (5). Furthermore, compound mutants with both the Oxtr and the prostaglandin F2␣ receptor deleted exhibit no defects in parturition, indicating significant redundancy in the birth process per se (5). However, in view of the established pharmacology of circulating OT on the uterine myometrium, the possibility of a physiological action of OT during childbirth cannot be excluded, even without a loss-of-function phenotype.Two other key actions of OT warrant mention: effects on social , behavior and on the regulation of food intake. Male OT Ϫ/Ϫ and Oxtr Ϫ/Ϫ mice show deficits in social recognition, without altered cognition or olfactory learning. That this social amnesia is a central rather than a peripheral action of OT is supported by the observation that recombinant OT injected directly into the amygdala rescues the defect (6). Compared with males, female OT or Oxtr null mice display anxiety and exaggerated stress responses, which are likewise mediated through central OT-ergic neurones (7). OT also is involved in the reg...

The oxytocin receptor has been suggested to be involved in energy metabolism, such as food intake and energy consumption. Here, we demonstrate that oxytocin receptor-deficient (Oxtr-/-) male mice exhibited late-onset obesity with increases in abdominal fat pads and fasting plasma triglycerides. Daily food intake and spontaneous motor activity of Oxtr-/- mice were not significantly different as compared with wild-type mice. In contrast, brown adipose tissue in Oxtr-/- mice contained large lipid droplets and cold-induced thermogenesis was impaired. This study demonstrates that oxytocin receptor plays essential roles in the regulation of energy homeostasis.