Phytoestrogen-containing diets offer benefits for mouse embryology but lead to fewer offspring being produced.

One of the most commonly used protein sources in rodent diets is soy, which is naturally rich in phytoestrogens. Although phytoestrogens have shown potential health benefits in humans, they may also have the ability to disrupt reproduction. Consequently, there has been a tendency to try to exclude them from rodent diets. In the current study, we investigated whether phytoestrogen content in the mouse diet could affect reproduction in mice used as embryo donors. Donor mice (C57BL/6JOlaHsd) were maintained with three different diets: high phytoestrogen (ca. 400 mg/kg genistein), low phytoestrogen (ca. 10 mg/kg genistein) and standard breeding diet (ca. 120 mg/kg genistein). Mice fed a high phytoestrogen diet had a high yield of plugs, embryos, and injectable embryos, as well as producing good quality embryos. Results from donor mice fed a low phytoestrogen diet were consistently but only slightly inferior, whereas mice fed a standard diet performed the poorest. Interestingly, the largest number of born and weaned offspring were observed when recipient females received embryos from the standard diet group. Sperm yield and quality of stud males did not differ between the groups. We surmize that for experimental endpoints requiring fertilized embryos it may be more beneficial to feed mice a diet containing phytoestrogen, but if the goal is to produce transgenic mice, a diet high in phytoestrogen may be inadvisable. In conclusion, care should be taken when selecting a diet for experimental mouse colonies as phytoestrogen could influence the study outcome.

Endothelial-specific YY1 governs sprouting angiogenesis through directly interacting with RBPJ.

Angiogenesis, the formation of new blood vessels, is tightly regulated by gene transcriptional programs. Yin Ying 1 (YY1) is a ubiquitously distributed transcription factor with diverse and complex biological functions; however, little is known about the cell-type-specific role of YY1 in vascular development and angiogenesis. Here we report that endothelial cell (EC)-specific YY1 deletion in mice led to embryonic lethality as a result of abnormal angiogenesis and vascular defects. Tamoxifen-inducible EC-specific YY1 knockout (YY1iΔEC ) mice exhibited a scarcity of retinal sprouting angiogenesis with fewer endothelial tip cells. YY1iΔEC mice also displayed severe impairment of retinal vessel maturation. In an ex vivo mouse aortic ring assay and a human EC culture system, YY1 depletion impaired endothelial sprouting and migration. Mechanistically, YY1 functions as a repressor protein of Notch signaling that controls EC tip-stalk fate determination. YY1 deficiency enhanced Notch-dependent gene expression and reduced tip cell formation. Specifically, YY1 bound to the N-terminal domain of RBPJ (recombination signal binding protein for Ig Kappa J region) and competed with the Notch coactivator MAML1 (mastermind-like protein 1) for binding to RBPJ, thereby impairing the NICD (intracellular domain of the Notch protein)/MAML1/RBPJ complex formation. Our study reveals an essential role of endothelial YY1 in controlling sprouting angiogenesis through directly interacting with RBPJ and forming a YY1-RBPJ nuclear repression complex.

Parameters of the Mouse Embryo Assay that affect detection of peroxides in mineral oil.

RESEARCH QUESTION: Can culture conditions influence the sensitivity of a Mouse Embryo Assay and its potential to detect peroxide-related toxicity in mineral oil samples? DESIGN: Protein type and concentration, embryo density and culture dish design were selected as the variables in the culture system with the potential to influence the assay's sensitivity. Fresh 1-cell mouse embryos were cultured under mineral oil samples with known peroxide concentrations. Protein type (human serum albumin [HSA] + α/ß-Globulins versus HSA versus bovine serum albumin [BSA]), concentration (5 mg/ml versus 0.5 mg/ml), embryo density (25 versus 3 µl/embryo) and culture dish (Petri versus micro-well dish) were adjusted to define the culture conditions with the highest sensitivity. RESULTS: High concentrations of peroxides can be easily detected by current quality control standards. However, for oil samples with a lower concentration of peroxides, supplementing the culture medium with 5 mg/ml of HSA + alpha/beta-globulins or with HSA resulted in an increased detection of embryo toxicity compared with when BSA was used as the protein supplement. The sensitivity of the assay was greatly reduced when embryos were cultured in groups and when certain micro-well dishes were used. CONCLUSIONS: Current quality control protocols may not be sensitive enough to identify low concentrations of peroxides, which, if undetected, can increase over time and become potentially harmful during gamete and embryo culture. The different parameters established in this study allow the sensitivity of the Mouse Embryo Assays to be optimized to specifically detect peroxides in mineral oil samples prior to their release into the market and their broad use in human IVF.

[Chrysin inhibits adipogenic differentiation of mouse embryonic fibroblasts].

Chrysin is an active flavonoid wildly presented in many herbs. It has the effect to reduce serum lipid. To investigate the effect of chrysin on the adipogenic differentiation of mouse embryonic fibroblasts, methyl thiazolyl tetrazolium (MTT) and crystal violet were used to detect the cytotoxic effect of chrysin on Immortalized mouse embryonic fibroblasts (iMEFs). Propidium iodide (PI) staining combined with flow cytometry (FCM) was employed to detect the effects of different concentrations of chrysin on iMEFs cell cycle. The effect of chrysin on adipogenic differentiation ability of iMEFs was determined by oil red O staining. Semi-quantitative PCR was employed to detect the effect of chrysin on mRNA transcriptional levels of adipogenic differentiation markers, including perilipin 2, adiponectin (adipoq), Fabp4, LPL, MCP-1 and adipogenic differentiation key transcription factor peroxisome proliferators-actiated receptor-gamma 2(PPAR-γ2). Results indicated that chrysin had certain cytotoxic effect for iMEFs in a dose-dependent manner, and the IC50 was identified nearly to 30 µmol•L⁻¹. FCM analysis showed that chrysin could affect the cell-cycle distribution of iMEFs, increasing the ratio of cells in G1 phase. Adipogenic differentiation inducing experiment showed that 30 µmol•L⁻¹ chrysin significantly reduced lipid drops accumulation induced by insulin and dexamethasone. In addition, the mRNA transcriptional levels of PPAR-γ2 and LPL were significantly decreased and mRNA levels of fabp 4, MCP-1, adipoq were also affected after chrysin treatment. The experiment results suggest that chrysin attenuates the adipogenic differentiation capacity of mesenchymal stem cells.

Zinc-deficient diet decreases fetal long bone growth through decreased bone matrix formation in mice.

This study evaluated the effects of zinc on skeletal development during fetal development in pregnant ICR mice fed a zinc-deficient (3 mg/kg) or zinc-adequate (30 mg/kg) diet. We also included a group pair-fed with the zinc-deficient group to control for decreased appetite due to zinc deficiency. Developing fetuses at embryonic day 18.5 were removed by cesarean section, and the skeletal development was evaluated by histological analysis as well as by body weight and longitudinal growth measurement. Reduced maternal food intake in the zinc-deficient and pair-fed groups resulted in a marked and significant (P < .05) decrease in fetal weight compared to that of the zinc-adequate group. However, fetal length retardation in the pair-fed group was less marked than in the zinc-deficient group, suggesting that reduced supply of zinc from maternal circulation may play a role in longitudinal growth through skeletal development. The fetal developing tibia of the zinc-deficient group showed marked shortening of diaphysis and a mild narrowing of the hypertrophic chondrocyte zone width with increased osteoclast number, but there was no influence on the mineralization of bone matrix. This may be the result of reduced activation of osteoblasts and maturation of chondrocytes with increased osteoclastic activity, suggesting that zinc deficiency during the fetal development has a greater impact on the matrix formation of bone than the mineralization of bone matrix.

A comparison study of effects of Echinacea extract and levamisole on phenytoin-induced cleft palate in mice.

There are many reports that the teratogenic effects of phenytoin, especially cleft palate can be decreased by stimulation of maternal immune system. Also, there is some evidence that Echinacea extract and levamisole are immunomodulator drugs. So, in this study, we compared the prophylactic effects of levamisole and Echinacea extract on teratogenic effects of phenytoin. This study was performed on 32 pregnant mice that were divided into four groups. The first group (control group) received normal saline intraperitoneally and the other groups (test groups) received phenytoin (65 mg/kg intraperitoneally) at 10th day of gestation. Levamisole and extract of Echinacea purpurea were administrated at dose of 10 and 360 mg/kg intraperitoneally, respectively, in along with and 12h later after phenytoin injection, in two groups. Fetuses were carried out in 19th day of gestation and after determination of weight and length; they were stained by Alizarin red-Alcian blue method. Cleft palate incidence was 16, 5.3, and 3.2% in fetuses of mice that received only phenytoin, phenytoin with levamisole, and phenytoin with Echinacea extract, respectively. Mean weight and length of fetuses of animals that received levamisole and Echinacea extract were significantly greater than those received only phenytoin. It is concluded that Echinacea can stimulate immune system more than levamisole and has better prophylactic effect on incidence of phenytoin-induced cleft palate, but it is not significant.

Conduction abnormality in gap junction protein connexin45-deficient embryonic stem cell-derived cardiac myocytes.

In early-stage heart, the cardiac impulse does not propagate through the specialized conduction system but spreads from myocyte to myocyte. We hypothesized that the gap junction protein connexin45 (Cx45) regulates early-stage contractions, because it is the only gap junction protein described in early hearts. Cx45-deficient (Cx45(-/-)) mice die of heart failure, concomitantly displaying other complex defects in the cardiovascular system. In order to determine the specific cardiac muscular function of Cx45, we created Cx45(-/-) embryonic stem (ES) cells to be differentiated into cardiac muscle in vitro. Unlike the coordinated contractions of wild-type cells, differentiated Cx45(-/-) cardiac myocytes showed high and irregular pulsation rates. Alterations of the electrophysiological properties of the Cx45(-/-) cardiac myocytes were indicated both by extracellular recording on planar multielectrode array probes and by intracellular Ca(2+) recording of the fluorescent Ca(2+) indicator fura-2. The in vitro system minimizes an influence of hemodynamic factors that complicate the phenotypes of Cx45(-/-) mice. Our results indicate that Cx45 is an essential connexin for coordinated conduction through early cardiac myocytes. The Supplementary Material referred to in this article can be found at the Anatomical Record website (http://www.interscience.wiley.com/jpages/0003-276X/suppmat).

Bono1: a gene associated with regions of deposition of bone and dentine.

We have examined the mRNA expression pattern of the murine expressed sequence tag (EST) clone in embryonic and early postnatal mice. Expression was strongly and specifically localised to developing bones and odontoblasts in teeth, therefore we have named this gene Bono1 (Bone and odontoblasts). Bono1, which has human, rat and chicken orthologues designated as FKSG28 was expressed in most ossification regions of the head including calvarial bones, skull and jaws. Expression was localised to osteoblasts derived from both intramembraneous and endochondral ossification processes. Comparative analysis of the expression of Bono1 in the mandible with Bone sialoprotein (BSP), a marker of advanced osteoblastogenesis, revealed that Bono1 expression starts later in the osteoblast cell lineage than BSP. In the tooth, Bono1 was localised in secretory odontoblasts. This expression was complementary to BSP, which was only present in early pre-odontoblasts. In secretory odontoblasts, Bono1 was shown to be co-expressed with Dentin sialophosphoprotein (DSPP). In summary, Bono1 was expressed in functional osteoblasts and odontoblasts and was associated with regions of matrix mineralization.

Cloning and characterization of the full-length mouse Ptk7 cDNA encoding a defective receptor protein tyrosine kinase.

The 3.8-kb full-length mouse Ptk7 cDNA encoding a defective receptor protein tyrosine kinase was cloned by reverse transcription-PCR of mouse liver mRNA. The mouse PTK7 polypeptide showed 92.6% identity to human PTK7. The mouse Ptk7 gene consists of 20 exons and has exactly the same exon structure as the human PTK7 gene. Mouse PTK7 was shown to be phosphorylated neither by itself nor by other protein tyrosine kinases. In addition, its expression did not affect the phospho-tyrosine level of cellular proteins in COS-1 cells. The mouse Ptk7 mRNA was expressed at high levels in lung and un-pregnant uterus among adult tissues, and in the tail, limbs, somites, gut, and craniofacial regions among embryonic tissues. These data suggest that mouse PTK7, an orthologue of human PTK7, plays multiple roles in embryonic development.

MyoR is expressed in nonmyogenic cells and can inhibit their differentiation.

The development of skeletal muscle in mammals is promoted by the muscle-specific basic helix-loop-helix transcription factors of the MyoD family. Evidence also suggests that there are basic helix-loop-helix proteins that specifically inhibit skeletal myogenesis, including Mtwist, Mist1, and the most recently described, MyoR. It has been suggested that MyoR expression is limited to the precursors of the skeletal muscle lineage and acts as a transcriptional repressor of the muscle differentiation program. However, our results demonstrate that MyoR is expressed in several different, nonmuscle adult tissues. Furthermore, MyoR is expressed in the embryonic ectoderm of blastocyst stage mouse embryos, well before skeletal muscle specification and even before delineation of the mesodermal germ layer. Using embryonic ectoderm analogous stem cells, we demonstrate that in these nonmuscle cells, as in skeletal muscle precursor cells, expression of MyoR is inversely correlated with the extent of cellular differentiation as induced by retinoic acid. Our preliminary results indicate that overexpression of exogenous MyoR inhibits retinoic-acid-induced differentiation in EC cells and is lethal to early mouse embryos. Our results suggest a much broader role for MyoR in the repression and/or determination of embryonic cell differentiation.

Cyp26C1 encodes a novel retinoic acid-metabolizing enzyme expressed in the hindbrain, inner ear, first branchial arch and tooth buds during murine development.

Retinoic acid (RA), an active metabolite of vitamin A, is a crucial signaling molecule involved in tissue morphogenesis during embryonic development. RA distribution and concentration is precisely regulated during embryogenesis by balanced complementary activities of RA synthesizing (RALDH) and metabolizing (CYP26) enzymes. Here, we describe the identification of a novel murine p450 cytochrome belonging to the CYP26 family, mCYP26C1. Sequence alignment show that mCYP26C1 is more closely related to mCYP26B1 than mCYP26A1. At early developmental stages (E8.0-E8.5), mCyp26C1 is expressed in prospective rhombomeres 2 and 4, in the first branchial arch and along the lateral surface mesenchyme adjacent to the rostral hindbrain. At E9.5, mCyp26C1 expression persists in rhombomere 2 and in the maxillary and mandibular components of the first branchial arch, and is strongly induced in the lateral cervical mesenchyme. By mid-gestation, mCyp26C1 is weakly expressed in the cervical mesenchyme and in the maxillary component of the first branchial arch. At E11.5, mCyp26C1 can only be seen in a narrow band in the lateral cervical mesenchyme. During late gestation, mCyp26C1 exhibits region-specific expression in the inner ear epithelium and a persistent expression in the inner dental epithelium of the developing teeth. This pattern of expression suggests that mCYP26C1 may play an important role in protecting the hindbrain, first branchial arch, otocyst and tooth buds against RA exposure during embryonic development.

Organization of the mouse dorsal thalamus based on topology, calretinin immnunostaining, and gene expression.

To better understand the organization and evolution of the dorsal thalamus, we have made a first approach to analyze the possible histogenetic compartments of the mammalian dorsal thalamus using mouse embryos. For that, we have analyzed the expression of the proneural gene Math4a and the protein calretinin. Our results suggest the existence of rostrodorsal, caudoventral, and ventral compartments in the embryonic dorsal thalamus of the mouse, which partly parallel the dorsoventral histogenetic tiers postulated in the dorsal thalamus of sauropsids. The rostrodorsal compartment of the mouse dorsal thalamus is characterized by expression of Math4a, and it appears to include sensory and motor thalamic nuclei projecting to the dorsal pallium (isocortex). This compartment appears equivalent to the lemnothalamus proposed by Butler in tetrapods based on hodological grounds. The caudoventral and ventral compartments of the mouse dorsal thalamus lack expression of Math4a in the mantle, but they are characterized by several populations of calretinin-immunorective neurons that show projections to the claustroamygdaloid region in the ventrolateral pallium. More studies will be needed to analyze if the compartments proposed in this study represent true histogenetic units, and to find homologous developmental fields in all vertebrates.

In vitro differentiation of mouse embryonic stem cells after activation by retinoic acid.

Embryonic stem (ES) cells are pluripotent cells isolated from the inner cell mass of blastocysts. ES cells are able to differentiate into the three primitive layers (endoderm, mesoderm, and ectoderm) of the organism, including the germline. In recent reports mouse ES cells have been successfully applied in the treatment of spinal cord injury, hereditary myelin disorder of the central nervous system, and diabetes mellitus. In this study, we investigated the induction of mouse ES cell differentiation, using culture of embryoid bodies (EBs) into the diverse tissues. EBs were formed by culturing ES cells (129/SV strain) in DMEM supplemented with 10% FBS, in the absence of feeder cells and leukemia inhibitory factor (LF). EBs were induced to differentiate by treatment with retinoic acid (RA). In control medium (non-RA medium) beating muscles, blood vessels, hemocytes, and cartilages were frequently observed in EBs. Moreover, when EBs were cultured in medium including RA (5 x 10(-8) M, and 5 x 10(-9) M), differentiation of the optic vesicle, lens, retina, and neural groove was observed. In this study we demonstrated that an efficient system for inducing the differentiation of ES cells using EBs.

Cyclin-dependent kinase 5-deficient mice demonstrate novel developmental arrest in cerebral cortex.

The cerebral cortex of mice with a targeted disruption in the gene for cyclin-dependent kinase 5 (cdk5) is abnormal in its structure. Bromodeoxyuridine labeling reveals that the normal inside-out neurogenic gradient is inverted in the mutants; earlier born neurons are most often found superficial to those born later. Despite this, the early preplate layer separates correctly and neurons with a normal, pyramidal morphology can be found between true marginal zone and subplate. Consistent with their identity as layer VI corticothalamic neurons, they can be labeled by DiI injections into thalamus. The DiI injections also reveal that the trajectories of the cdk5(-/-) thalamocortical axons are oblique and cut across the entire cortical plate, instead of being oriented tangentially in the subcortical white matter. We propose a model in which the cdk5(-/-) defect blocks cortical development at a heretofore undescribed intermediate stage, after the splitting of the preplate, but before the migration of the full complement of cortical neurons.

Combinatorial expression patterns of individual TLE proteins during cell determination and differentiation suggest non-redundant functions for mammalian homologs of Drosophila Groucho.

The Drosophila protein Groucho is involved in the regulation of cell-determination events during insect neurogenesis and segmentation. A group of mammalian proteins, referred to as transducin-like Enhancer of split (TLE) 1 through 4, share with Groucho identical structures and molecular properties. The aim was to determine whether individual TLE proteins participate in the regulation of cell determination in mammals like their Drosophila counterpart. It is here reported that TLE family members are expressed in combinatorial ways during the in vitro differentiation of mouse P19 embryonic carcinoma cells (a model for neural determination) and rat CFK2 cells (a model for chondrocytic determination). TLE1 is up-regulated and TLE2 and TLE4 are down-regulated to different extents during early stages of differentiation. In contrast, later stages correlate with up-regulation of TLE2 and TLE4, and decreased expression of TLE1. Individual TLE proteins are also expressed in combinatorial as well as complementary patterns during the development of the cerebral cortex and spinal cord of mouse embryos. In particular, TLE1 is robustly expressed in both neural progenitor cells and postmitotic neurons of the outer layers of the cortical plate, whereas TLE4 expression marks preferentially postmitotic neurons of the inner layers. Taken together, these results strongly suggest non-redundant roles for individual TLE proteins during both cell-determination and cell-differentiation events.

Modulation of commitment, proliferation, and differentiation of chondrogenic cells in defined culture medium.

The factors regulating the growth and development of mesenchymal precursor cells toward chondrogenesis are not well identified. We have developed a defined serum-free culture system that allows the proliferation of chick embryo chondrogenic cells and their maturation toward hypertrophic chondrocytes. Proliferation is obtained in adhesion in medium supplemented with insulin (Ins), Dexamethasone (Dex), and either basic fibroblast growth factor (FGF-2), platelet-derived growth factor bb, epithelial growth factor, or GH; the highest mitogenic response is induced by FGF-2 in synergy with Ins. Ins can be substituted by Ins-like growth factor I. When these cells are transferred into suspension culture in Ins/Dex and T3 without growth factor supplement, they undergo the complete chondrogenic development characterized by type X collagen synthesis and cellular hypertrophy. During differentiation, Ins cannot be substituted by Ins-like growth factor I. Chondrogenesis is also evidenced by the formation of hypertrophic cartilage when the medium is supplemented with ascorbic acid. If T3 is introduced in the proliferation phase, the cells fail to differentiate to hypertrophy in suspension unless bone morphogenetic protein-2 is added. Assays of ectopic tissue formation in nude mice, with cells implanted sc after adsorption on collagen sponge or porous hydroxyapatite ceramics, indicate that cells grown in Ins/FGF-2 reform mainly cartilage in vivo, whereas expansion in Ins/T3/Dex/FGF-2 leads to the formation of cartilage, bone, and adipose tissue.

Characterization of an expanded glutamine repeat androgen receptor in a neuronal cell culture system.

Spinal and bulbar muscular atrophy (SBMA) is an inherited form of lower motor neuron degeneration caused by expansion of a CAG repeat in the androgen receptor (AR) gene. To study the mechanism by which this mutation causes neuronal pathology, we stably transfected a motor neuron hybrid cell line with human AR cDNAs containing either 24 or 65 repeats (AR24 and AR65, respectively). Both forms of receptor were able to bind ligand and activate transcription of a reporter construct equally well. Likewise, the subcellular localizations of AR24 and AR65 were similar, in both the presence and the absence of ligand. AR24- and AR65-expressing clones were phenotypically indistinguishable. They survived equally well after differentiation and were equally susceptible to damage by oxidative stress. Our studies thus demonstrate that, in a neuronal system, the expanded repeat AR functions like the normal repeat AR in several important ways. Because levels of AR65 expression were consistently lower than levels of AR24 expression, we propose that the loss of function of AR seen in SBMA may be due to decreased levels of receptor expression rather than to a difference in intrinsic properties. The postulated gain of function responsible for neuronal degeneration remains to be determined.

Myelin transcription factor 1 (Myt1) of the oligodendrocyte lineage, along with a closely related CCHC zinc finger, is expressed in developing neurons in the mammalian central nervous system.

The establishment and operation of the nervous system requires genetic regulation by a network of DNA-binding proteins, among which is the zinc finger superfamily of transcription factors. We have cloned and characterized a member of the unusual Cys-Cys-His-Cys (also referred to as Cys2HisCys, CCHC, or C2HC) class of zinc finger proteins in the developing nervous system. The novel gene, Myt1-like (Myt1l), is highly homologous to the original representative of this class, Myelin transcription factor 1 (Myt1) (Kim and Hudson, 1992). The MYT1 gene maps to human chromosome 20, while MYT1L maps to a region of human chromosome 2. Both zinc finger proteins are found in neurons at early stages of differentiation, with germinal zone cells displaying intense staining for MyT1. Unlike Myt1, Myt1l has not been detected in the glial lineage. Neurons that express Myt1l also express TuJ1, which marks neurons around the period of terminal mitosis. The Myt1l protein resides in distinct domains within the neuronal nucleus, analogous to the discrete pattern previously noted for Myt1 (Armstrong et al.: 14:303-321, 1995). The developmental expression and localization of these two multifingered CCHC proteins suggests that each may play a role in the development of neurons and oligodendroglia in the mammalian central nervous system.

Inhibitors and promoters of thalamic neuron adhesion and outgrowth in embryonic neocortex: functional association with chondroitin sulfate.

When embryonic thalamic neurons are plated onto living slices of mouse forebrain, cell attachment and neurite outgrowth on different layers of the developing cerebral cortex vary dramatically, in ways that correlate with the timing and pattern of thalamocortical innervation. These layer-specific differences can be eliminated from embryonic day 16 slices by enzymatic removal of chondroitin sulfate (CS). The cortical plate (a zone avoided by thalamic axons in vivo) possesses inhibitory activity (anti-adhesive, neurite repelling) and the intermediate zone and subplate (in which thalamic axons normally grow) possess stimulatory activity (adhesive, neurite promoting), both of which are chondroitinase sensitive. These opposing activities appear not to reflect the presence of different CS proteoglycans (CSPGs) in different zones, but rather the presence of differentially localized CS-binding molecules, which can be competed away by soluble CS. This model reconciles conflicting reports on the actions of CSPGs in neural development, and suggests a role for CSPGs in the organization of matrix-bound cues in the brain.

Molecular cloning and characterization of a mouse nuclear orphan receptor expressed in embryos and testes.

A mouse cDNA encoding a putative DNA-binding protein of the zinc-finger type was isolated from an E8.5 mouse embryonic cDNA library. Sequence comparison revealed a high degree of homology between this mouse cDNA and the human and rat orphan receptor Tr2-11 isolated from prostate cDNA libraries. This transcript was detected in early-to-midgestation embryos and was seen to level off during later stages of development. In adult animals, a high level of expression was detected only in the testis, starting at postnatal day 18, a stage when active meiosis begins to occur. A specific antibody was raised, and immunoreactive signal was specifically located in the adlumenal compartment of the seminiferous tubule, where advanced germ cells reside. In mice fed a vitamin A-depleted diet, where the testes were depleted of advanced germ cells, expression of this protein could not be detected, suggesting a biological relation of this orphan receptor and male germ-cell differentiation. Using a retinoic acid response element (RARE)-containing reporter system, it was demonstrated that expression of this protein dramatically repressed both the basal and the retinoic acid (RA)-regulated promoter activities of this reporter. Thus, this orphan receptor could play a role in modulating both the basic transcription machinery and the RA signalling pathway during embryogenesis and male germ-cell differentiation.