Immunohistochemical and Immunoelectron Microscopical Distribution of MEGF8 in the Mouse Central Nervous System

Mutations in multiple epidermal growth factor-like domain 8 (MEGF8), a multidomain transmembrane protein encoded by a gene conserved across species, cause Carpenter's syndrome, which is associated with learning disabilities, mental health issues, and left-right patterning abnormalities. MEGF8 interacts with MGRN1, a protein that functions as an E3 ubiquitin ligase and is involved in multiple physiological and pathological processes. However, the mechanism underlying the distribution of MEGF8 in the central nervous system (CNS) and its cellular and subcellular locations remain unknown. This study aimed to map MEGF8 in the mouse CNS using a new antibody. We discovered that MEGF8 was distributed in the majority of neuronal cell somata across most CNS regions. High levels of MEGF8 were expressed in the neuropils of the CNS gray matter. Immunoelectron microscopy showed that MEGF8 was present in the synapses and around the outer mitochondrial membrane. These findings show that MEGF8 is uniformly distributed throughout the mouse CNS, and its distribution indicates that it plays a substantial role in synaptic and mitochondrial functions. To the best of our knowledge, this is the first study to document MEGF8 distribution in the CNS.

The conserved MASRPF motif in the Attractin homolog, Distracted, is required for association with Drosophila E3-ligase Mgrn1

In rodents, all three paralogs of the Attractin (Atrn) transmembrane protein family exhibit strong phenotypic overlap and are implicated in the regulation of the same G-protein coupled receptors (GPCR) as E3-ligase Mahogunin ring finger 1 (Mgrn1). Recently it was shown that the highly conserved intracellular MASRPF motif in mammal Multiple epidermal growth factor-like domain 8 protein is required for binding of Mgrn1 to mediate ubiquitination of GPCR Smoothened in vitro. Here, we show that the MASRPF motif of Drosophila Distracted, the ortholog of ATRN and Attractin-like 1, is required for association with Drosophila Mgrn1 (dMgrn1) in vivo.

A big-data approach to understanding metabolic rate and response to obesity in laboratory mice

Maintaining a healthy body weight requires an exquisite balance between energy intake and energy expenditure. To understand the genetic and environmental factors that contribute to the regulation of body weight, an important first step is to establish the normal range of metabolic values and primary sources contributing to variability. Energy metabolism is measured by powerful and sensitive indirect calorimetry devices. Analysis of nearly 10,000 wild-type mice from two large-scale experiments revealed that the largest variation in energy expenditure is due to body composition, ambient temperature, and institutional site of experimentation. We also analyze variation in 2329 knockout strains and establish a reference for the magnitude of metabolic changes. Based on these findings, we provide suggestions for how best to design and conduct energy balance experiments in rodents. These recommendations will move us closer to the goal of a centralized physiological repository to foster transparency, rigor and reproducibility in metabolic physiology experimentation.

Prolidase enzyme is required for extracellular matrix integrity and impacts on postnatal cerebellar cortex development

The extracellular matrix is essential for brain development, lamination, and synaptogenesis. In particular, the basement membrane below the pial meninx (pBM) is required for correct cortical development. The last step in the catabolism of the most abundant protein in pBM, collagen Type IV, requires prolidase, an exopeptidase cleaving the imidodipeptides containing pro or hyp at the C-terminal end. Mutations impairing prolidase activity lead in humans to the rare disease prolidase deficiency characterized by severe skin ulcers and mental impairment. Thus, the dark-like (dal) mouse, in which the prolidase is knocked-out, was used to investigate whether the deficiency of prolidase affects the neuronal maturation during development of a brain cortex area. Focusing on the cerebellar cortex, thinner collagen fibers and disorganized pBM were found. Aberrant cortical granule cell proliferation and migration occurred, associated to defects in brain lamination, and in particular in maturation of Purkinje neurons and formation of synaptic contacts. This study deeply elucidates a link between prolidase activity and neuronal maturation shedding new light on the molecular basis of functional aspects in the prolidase deficiency.

Lack of prolidase causes a bone phenotype both in human and in mouse

The degradation of the main fibrillar collagens, collagens I and II, is a crucial process for skeletal development. The most abundant dipeptides generated from the catabolism of collagens contain proline and hydroxyproline. In humans, prolidase is the only enzyme able to hydrolyze dipeptides containing these amino acids at their C-terminal end, thus being a key player in collagen synthesis and turnover. Mutations in the prolidase gene cause prolidase deficiency (PD), a rare recessive disorder. Here we describe 12 PD patients, 9 of whom were molecularly characterized in this study. Following a retrospective analysis of all of them a skeletal phenotype associated with short stature, hypertelorism, nose abnormalities, microcephaly, osteopenia and genu valgum, independent of both the type of mutation and the presence of the mutant protein was identified. In order to understand the molecular basis of the bone phenotype associated with PD, we analyzed a recently identified mouse model for the disease, the dark-like (dal) mutant. The dal/dal mice showed a short snout, they were smaller than controls, their femurs were significantly shorter and pQCT and μCT analyses of long bones revealed compromised bone properties at the cortical and at the trabecular level in both male and female animals. The differences were more pronounce at 1 month being the most parameters normalized by 2 months of age. A delay in the formation of the second ossification center was evident at postnatal day 10. Our work reveals that reduced bone growth was due to impaired chondrocyte proliferation and increased apoptosis rate in the proliferative zone associated with reduced hyperthrophic zone height. These data suggest that lack of prolidase, a cytosolic enzyme involved in the final stage of protein catabolism, is required for normal skeletogenesis especially at early age when the requirement for collagen synthesis and degradation is the highest.

Expression of Attractin in male reproductive tract of human and mice and its correlation with male reproduction

The expression of Attractin mRNA and protein in testis and semen of human and male mice was investigated. Human testis and semen samples were all collected from Reproductive Center of Renmin Hospital, Wuhan University in December, 2012. Testis samples were collected from 7 cases of obstructive azoospermias when they were subjected to diagnosed testis biopsy, and 30 normal human semen samples were obtained from those cases of semen analysis. Adult mice testis tissues were obtained from 10 2-month-old male BALB/c mice, and 60 male mice at different ages were classified into 10 groups (day 1, 5, 10, 15, 21, 28, 35, 42, 56, and 120 respectively, n=6 each). The expression of Attractin mRNA and protein in testis was detected by RT-PCR and Western blotting respectively. Human semen samples were centrifuged into sperm plasma (SP) and sperm extract (SE), and mice sperm samples were collected from the epididymis of 10 adult male BALB/c mice. Western blotting was used to determine the Attractin protein expression level. Attractin mRNA and protein were expressed in the testis of both patients with obstructive azoospermias and adult Bcl/B mice. Quantitative RT-PCR revealed that no Attractin mRNA was detectable in day 1 male BALB/c mice group. The Attractin mRNA and protein levels were low on the day 10, and increased with age until day 56. On the day 120, the expression levels of Attractin were decreased. As for human semen samples, Attractin protein was expressed in both SP and SE, but didn't exist in samples from the epididymis of male BALB/c mice. It was suggested that Attractin acted as a novel active substance and was involved in male reproduction in both human and BALB/c mice, but it exerted a different expression profile in different mammal species.

RML prions act through Mahogunin and Attractin-independent pathways

While the conversion of the normal form of prion protein to a conformationally distinct pathogenic form is recognized to be the primary cause of prion disease, it is not clear how this leads to spongiform change, neuronal dysfunction and death. Mahogunin ring finger-1 (Mgrn1) and Attractin (Atrn) null mutant mice accumulate vacuoles throughout the brain that appear very similar to those associated with prion disease, but they do not accumulate the protease-resistant scrapie form of the prion protein or become sick. A study demonstrating an interaction between cytosolically-exposed prion protein and MGRN1 suggested that disruption of MGRN1 function may contribute to prion disease pathogenesis, but we recently showed that neither loss of MGRN1 nor MGRN1 overexpression influences the onset or progression of prion disease following intracerebral inoculation with Rocky Mountain Laboratory prions. Here, we show that loss of ATRN also has no effect on prion disease onset or progression and discuss possible mechanisms that could cause vacuolation of the central nervous system in Mgrn1 and Atrn null mutant mice and whether the same pathways might contribute to this intriguing phenotype in prion disease.

Morphology of mouse external genitalia: implications for a role of estrogen in sexual dimorphism of the mouse genital tubercle

PURPOSE

We examined the role of androgens and estrogens in mammalian sexual differentiation by morphological characterization of adult wt and mutant mouse external genitalia. We tested the hypothesis that external genitalia development depends on androgen and estrogen action.

MATERIALS AND METHODS

We studied serial sections of the external genitalia of the CD-1 and C57BL6 wt strains of adult mice (Charles River Laboratories, Wilmington, Massachusetts). We recorded linear measurements of key structures in each specimen, including the urethra, erectile tissue, bone and cartilage. We used similar methodology to analyze mice mutant for estrogen receptor α (αERKO) and androgen receptor (X(Tfm)/Y) (Jackson Laboratory, Bar Harbor, Maine).

RESULTS

Morphology in X(Tfm)/Y adult murine external genitalia was remarkably similar to that in wt females. Bone and clitoral length was similar in wt females and X(Tfm)/Y mice. Conversely the αERKO clitoris was 59% longer and bone length in αERKO females was many-fold longer than that in female wt mice or X(Tfm)/Y mutants. The αERKO clitoris contained cartilage, which is typical of the wt penis but never observed in the wt clitoris. Serum testosterone was not increased in female αERKO mice 10 days postnatally when sex differentiation occurs, suggesting that masculinization of the αERKO clitoris is not a function of androgen.

CONCLUSIONS

Masculinization of the αERKO clitoris suggests a role for estrogen in the development of female external genitalia. We propose that normal external genital development requires androgen and estrogen action.

Shades of meaning: the pigment-type switching system as a tool for discovery

The pigment-type switching system, which controls whether melanocytes produce black/brown eumelanin or yellow/red pheomelanin, is responsible for many familiar coat coloration patterns in both domestic and wild mammals. In conjunction with the accessory proteins attractin and mahogunin ring finger 1, endogenous agonists and antagonists modulate signaling by the melanocortin 1 receptor to determine pigment type. Mutations in pigment-type switching genes can cause a variety of pleiotropic phenotypes, and these are often similar between mutants at different loci because the proteins encoded by these genes act together as part of conserved molecular pathways that are deployed in multiple biological contexts. When this is the case, pigment-type switching provides a powerful model system for elucidating the shared molecular mechanisms underlying the pigmentary and non-pigmentary phenotypes. This review outlines the current understanding of the pigment-type switching pathway and discusses the opportunities that exist for exploring the molecular basis of pleiotropic phenotypes using this model system.

On the track of the white tiger: pigmentation could be linked to prion diseases, and location explains why

Certain rodent pigmentation mutants spontaneously develop brain spongiform changes. It is hypothesized that animals, and possibly humans, characterized by certain pigmentation gene variants could be more susceptible to prion diseases, which are characterized by this type of neuropathology. This hypothesis could be explained by the common location of the prion protein and several important pigmentation genes in the same chromosome. This common location can promote the joint transfer of both pigmentary and prion protein genes to the progeny. Pigmentation genes could also play a role in regulating protein folding and aggregation. Understanding the relationship between pigmentation genes and prion genes could lead to identify pigmentation variants at higher risk of prion diseases and understand the etiopathogenesis of these still invariably lethal disorders.