Musashi Exerts Control of Gonadotrope Target mRNA Translation During the Mouse Estrous Cycle.

The anterior pituitary controls key biological processes, including growth, metabolism, reproduction, and stress responses through distinct cell types that each secrete specific hormones. The anterior pituitary cells show a remarkable level of cell type plasticity that mediates the shifts in hormone-producing cell populations that are required to meet organismal needs. The molecular mechanisms underlying pituitary cell plasticity are not well understood. Recent work has implicated the pituitary stem cell populations and specifically, the mRNA binding proteins of the Musashi family in control of pituitary cell type identity. In this study we have identified the target mRNAs that mediate Musashi function in the adult mouse pituitary and demonstrate the requirement for Musashi function in vivo. Using Musashi RNA immunoprecipitation, we identify a cohort of 1184 mRNAs that show specific Musashi binding. Identified Musashi targets include the Gnrhr mRNA, which encodes the gonadotropin-releasing hormone receptor (GnRHR), and the Fshb mRNA, encoding follicle-stimulating hormone (FSH). Reporter assays reveal that Musashi functions to exert repression of translation of the Fshb mRNA, in addition to the previously observed repression of the Gnrhr mRNA. Importantly, mice engineered to lack Musashi in gonadotropes demonstrate a failure to repress translation of the endogenous Gnrhr and Fshb mRNAs during the estrous cycle and display a significant heterogeneity in litter sizes. The range of identified target mRNAs suggests that, in addition to these key gonadotrope proteins, Musashi may exert broad regulatory control over the pituitary proteome in a cell type-specific manner.

Comprehensive motor testing in Fmr1-KO mice exposes temporal defects in oromotor coordination.

Fragile X syndrome (FXS; MIM #300624), a well-recognized form of inherited human mental retardation is caused, in most cases, by a CGG trinucleotide repeat expansion in the 5'-untranslated region of FMR1, resulting in reduced expression of the fragile X mental retardation protein (FMRP). Clinical features include macroorchidism, anxiety, mental retardation, motor coordination, and speech articulation deficits. The Fmr1 knockout (Fmr1-KO) mouse, a mouse model for FXS, has been shown to replicate the macroorchidism, cognitive deficits, and neuroanatomical abnormalities found in human FXS. Here we asked whether Fmr1-KO mice also display appendicular and oromotor deficits comparable to the ataxia and dysarthric speech seen in FXS patients. We employed standard motor tests for balance and appendicular motor coordination, and used a novel long-term fluid-licking assay to investigate oromotor function in Fmr1-KO mice and their wild-type (WT) littermates. Fmr1-KO mice performed equally well as their WT littermates on standard motor tests, with the exception of a raised-beam task. However, Fmr1-KO mice had a significantly slower licking rhythm than their WT littermates. Deficits in rhythmic fluid-licking in Fmr1-KO mice have been linked to cerebellar pathologies. It is believed that balance and motor coordination deficits in FXS patients are caused by cerebellar neurophathologies. The neuronal bases of speech articulation deficits in FXS patients are currently unknown. It is yet to be established whether similar neuronal circuits control rhythmic fluid-licking pattern in mice and speech articulation movement in humans.

Normal social seeking behavior, hypoactivity and reduced exploratory range in a mouse model of Angelman syndrome.

BACKGROUND: Angelman syndrome (AS) is a neurogenetic disorder characterized by severe developmental delay with mental retardation, a generally happy disposition, ataxia and characteristic behaviors such as inappropriate laughter, social-seeking behavior and hyperactivity. The majority of AS cases are due to loss of the maternal copy of the UBE3A gene. Maternal Ube3a deficiency (Ube3a m-/p+), as well as complete loss of Ube3a expression (Ube3a m-/p-), have been reproduced in the mouse model used here. RESULTS: Here we asked if two characteristic AS phenotypes - social-seeking behavior and hyperactivity - are reproduced in the Ube3a deficient mouse model of AS. We quantified social-seeking behavior as time spent in close proximity to a stranger mouse and activity as total time spent moving during exploration, movement speed and total length of the exploratory path. Mice of all three genotypes (Ube3a m+/p+, Ube3a m-/p+, Ube3a m-/p-) were tested and found to spend the same amount of time in close proximity to the stranger, indicating that Ube3a deficiency in mice does not result in increased social seeking behavior or social dis-inhibition. Also, Ube3a deficient mice were hypoactive compared to their wild-type littermates as shown by significantly lower levels of activity, slower movement velocities, shorter exploratory paths and a reduced exploratory range. CONCLUSIONS: Although hyperactivity and social-seeking behavior are characteristic phenotypes of Angelman Syndrome in humans, the Ube3a deficient mouse model does not reproduce these phenotypes in comparison to their wild-type littermates. These phenotypic differences may be explained by differences in the size of the genetic defect as ~70% of AS patients have a deletion that includes several other genes surrounding the UBE3A locus.

Impairment of contextual conditioned fear extinction after microinjection of alpha-1-adrenergic blocker prazosin into the medial prefrontal cortex.

Long-lasting memories of aversive or stressful events have been associated with the noradrenergic system activation. Alpha-1-adrenergic antagonist prazosin has successfully been used in the last years to treat anxiety disorders related to aversive memories recurrence in humans. Contextual conditioned fear extinction paradigm in rats has been used to better understand the mechanisms involved in the attenuation of defensive behaviour after a traumatic situation. Here we investigated the effects of systemic administration of prazosin in the fear extinction processes. Rats were previously paired in a contextual fear conditioning box (1 footshock, 1 mA, 2s duration), further returning to the same box during three consecutive days receiving an intraperitoneal injection of vehicle or prazosin 30 min before (acquisition of extinction; 0.1 or 0.5mg/kg) or immediately after (consolidation of extinction, 0.5 or 1.5mg/kg) each extinction session (10 min). On the last day, all animals were re-exposed undrugged to the apparatus. Since the medial prefrontal cortex (mPFC) has been described as a key structure in the modulation of conditioned fear extinction, the effects of intra-mPFC microinjection (0.2 microl per side) of vehicle (PBS) or prazosin (0.75 or 2.5 nmol) in the acquisition of fear extinction (10 min before extinction session 1) were further evaluated. Subjects were drug-free re-exposed to the same box in the next day (extinction session 2). The percentage of freezing time was used as the memory retention parameter. The results showed that either systemic or intra-mPFC-alpha-1-adrenergic blockade increased the freezing time in the last extinction sessions, suggesting impairment of the extinction of contextual conditioned fear in rats.