'Neonatal' Nav1.2 reduces neuronal excitability and affects seizure susceptibility and behaviour

Developmentally regulated alternative splicing produces 'neonatal' and 'adult' isoforms of four Na(+) channels in human brain, NaV1.1, NaV1.2, NaV1.3 and NaV1.6. Heterologously expressed 'neonatal' NaV1.2 channels are less excitable than 'adult' channels; however, functional importance of this difference is unknown. We hypothesized that the 'neonatal' NaV1.2 may reduce neuronal excitability and have a seizure-protective role during early brain development. To test this hypothesis, we generated NaV1.2(adult) mice expressing only the 'adult' NaV1.2, and compared the firing properties of pyramidal cortical neurons, as well as seizure susceptibility, between the NaV1.2(adult) and wild-type (WT) mice at postnatal day 3 (P3), when the 'neonatal' isoform represents 65% of the WT NaV1.2. We show significant increases in action potential firing in NaV1.2(adult) neurons and in seizure susceptibility of NaV1.2(adult) mice, supporting our hypothesis. At postnatal day 15 (P15), when 17% of the WT NaV1.2 is 'neonatal', the firing properties of NaV1.2(adult) and WT neurons converged. However, inhibitory postsynaptic currents in NaV1.2(adult) neurons were larger and the expression level of Scn2a mRNA was 24% lower compared with the WT. The enhanced seizure susceptibility of the NaV1.2(adult) mice persisted into adult age. The adult NaV1.2(adult) mice also exhibited greater risk-taking behaviour. Overall, our data reveal a significant impact of 'neonatal' NaV1.2 on neuronal excitability, seizure susceptibility and behaviour and may contribute to our understanding of NaV1.2 roles in health and diseases such as epilepsy and autism.

Ndfip1 is required for the development of pyramidal neuron dendrites and spines in the neocortex

Ubiquitin ligases of the Nedd4 family are important for axon and dendrite development, but little is known about their adaptor, Nedd4 family-interacting protein 1 (Ndfip1), that is responsible for their enzymatic activation. To study the function of Ndfip1 in cortical development, we generated a conditional knock-out (conditional KO) in neurons. The Ndfip1 conditional KO mice were viable; however, cortical neurons in the adult brain exhibited atrophic characteristics, including stunted dendritic arbors, blebbing of dendrites, and fewer dendritic spines. In electron micrographs, these neurons appeared shrunken with compacted somata and involutions of the nuclear membrane. In culture, Ndfip1 KO neurons exhibited exuberant sprouting suggesting loss of developmental control. Biochemical analysis of postsynaptic density (PSD) fractions from Ndfip1 KO cortical and hippocampal neurons showed that the postsynaptic proteins (Arc and PSD-95) were reduced compared with wild-type controls. In addition, the PI3 kinase/Akt signaling pathway was altered. These results indicate that Ndfip1, through its Nedd4 effectors, is important for the development of dendrites and dendritic spines in the cortex.

Altered speeds and trajectories of neurons migrating in the ventricular and subventricular zones of the reeler neocortex

The Reelin signaling pathway is essential for proper cortical development, but it is unclear to whether Reelin function is primarily important for cortical layering or neuron migration. It has been proposed that Reelin is perhaps required only for somal translocation but not glial-dependent locomotion. This implies that the location of neurons responding to Reelin is restricted to the outer regions of the cortical plate (CP). To determine whether Reelin is required for migration outside of the CP, we used time-lapse imaging to track the behavior of cells undergoing locomotion in the germinal zones. We focused on the migratory activity in the ventricular/subventricular zones where the first transition of bipolar to multipolar migration occurs and where functional Reelin receptors are known to be expressed. Despite Reelin loss, neurons had no difficulty in undergoing radial migration and indeed displayed greater migratory speed. Additionally, compared with the wild-type, reeler neurons displayed altered trajectories with greater deviation from a radial path. These results suggest that Reelin loss has early consequences for migration in the germinal zones that are portrayed as defective radial trajectories and migratory speeds. Together, these abnormalities can give rise to the increased cell dispersion observed in the reeler cortex.

Cortical layer development and orientation is modulated by relative contributions of reelin-negative and -positive neurons in mouse chimeras

Reelin is an important protein that is indispensable for cortical lamination. In the absence of Reelin, cortical layers fail to form due to inappropriate neuron migration and positioning. The inversion of cortical layers is attributed to failure of neurons to migrate past earlier-generated neurons although how Reelin-insufficiency causes this is unclear. The issue is complicated by recent studies showing that very little Reelin is required for cortical layering. To test how variation in the number of Reelin-producing cells is linked to cortical lamination, we have employed Reelin(+/+) <--> Reelin(-/-) chimeras in which the number of Reelin-expressing neurons is adjusted. We found that the Reeler phenotype was rescued in chimeras with a large contribution of Reelin(+/+) neurons; conversely in chimeras with a weak contribution by Reelin(+/+) neurons, the mutant phenotype remained. However, increasing the number of Reelin(+/+) neurons beyond an unknown threshold resulted in partial rescue, with the formation of a correctly layered secondary cortex lying on top of an inverted mutant cortex. Therefore, the development of cortical layers in the correct order requires a minimal level of Reelin protein to be present although paradoxically, this is insufficient to prevent the simultaneous formation of inverted cortical layers in the same hemisphere.

Seizure-related gene 6 (Sez-6) in amacrine cells of the rodent retina and the consequence of gene deletion

Background

Seizure-related gene 6 (Sez-6) is expressed in neurons of the mouse brain, retina and spinal cord. In the cortex, Sez-6 plays a role in specifying dendritic branching patterns and excitatory synapse numbers during development.

Methodology/Principal Findings

The distribution pattern of Sez-6 in the retina was studied using a polyclonal antibody that detects the multiple isoforms of Sez-6. Prominent immunostaining was detected in GABAergic, but not in AII glycinergic, amacrine cell subpopulations of the rat and mouse retina. Amacrine cell somata displayed a distinct staining pattern with the Sez-6 antibody: a discrete, often roughly triangular-shaped bright spot positioned between the nucleus and the apical dendrite superimposed over weaker general cytoplasmic staining. Displaced amacrines in the ganglion cell layer were also positive for Sez-6 and weaker staining was occasionally observed in neurons with the morphology of alpha ganglion cells. Two distinct Sez-6 positive strata were present in the inner plexiform layer in addition to generalized punctate staining. Certain inner nuclear layer cells, including bipolar cells, stained more weakly and diffusely than amacrine cells, although some bipolar cells exhibited a perinuclear “bright spot” similar to amacrine cells. In order to assess the role of Sez-6 in the retina, we analyzed the morphology of the Sez-6 knockout mouse retina with immunohistochemical markers and compared ganglion cell dendritic arbor patterning in Sez-6 null retinae with controls. The functional importance of Sez-6 was assessed by dark-adapted paired-flash electroretinography (ERG).

Conclusions

In summary, we have reported the detailed expression pattern of a novel retinal marker with broad cell specificity, useful for retinal characterization in rodent experimental models. Retinal morphology, ganglion cell dendritic branching and ERG waveforms appeared normal in the Sez-6 knockout mouse suggesting that, in spite of widespread expression of Sez-6, retinal function in the absence of Sez-6 is not affected.

Oligodendrocyte positioning in cerebral cortex is independent of projection neuron layering

The factors affecting normal oligodendrocyte positioning in the cerebral cortex are unknown. Apart from the white matter, the highest numbers of oligodendrocytes in the rodent cortex are found in Layers V/VI, where the infragranular neurons normally reside. Few, if any, oligodendrocytes are normally found in the superficial cortical layers. To test whether or not this asymmetric positioning of oligodendrocytes is linked to the lamina positions of Layer V/VI projection neurons, mutant mice that cause neuronal layer inversion were examined. In three lines of mutant mice (Reeler, disabled-1, and p35) examined, representing two different genetic signaling pathways, the oligodendrocyte distribution was altered from an asymmetric to a symmetric distribution pattern. Unlike cortical neurons that are inverted in these mutant mice, the lack of oligodendrocyte inversion suggests a decoupling of the genetic mechanisms governing neuronal versus oligodendrocyte patterning. We conclude that oligodendrocyte positioning is not linked to the layer positions of V/VI projection neurons.

Initial characterization of PTH-related protein gene-driven lacZ expression in the mouse

The PTHrP gene generates low-abundance mRNA and protein products that are not easily localized by in situ hybridization histochemistry or immunohistochemistry. We report here a PTHrP-lacZ knockin mouse in which beta-gal activity seems to provide a simple and sensitive read-out of PTHrP gene expression.

INTRODUCTION

PTH-related protein (PTHrP) is widely expressed in fetal and adult tissues, typically as low-abundance mRNA and protein products that maybe difficult to localize by conventional methods. We created a PTHrP-lacZ knockin mouse as a means of surveying PTHrP gene expression in general and of identifying previously unrecognized sites of PTHrP expression.

MATERIALS AND METHODS

We created a lacZ reporter construct under the control of endogenous PTHrP gene regulatory sequences. The AU-rich instability sequences in the PTHrP 3' untranslated region (UTR) were replaced with SV40 sequences, generating products with lacZ/beta gal kinetics rather than those of PTHrP. A nuclear localization sequence was not present in the construct.

RESULTS

We characterized beta-galactosidase (beta-gal) activity in embryonic whole mounts and in the skeleton in young and adult animals. In embryos, we confirmed widespread PTHrP expression in many known sites and in several novel epidermal appendages (nail beds and footpads). In costal cartilage, beta-gal activity localized to the perichondrium but not the underlying chondrocytes. In the cartilaginous molds of forming long bones, beta-gal activity was first evident at the proximal and distal ends. Shortly after birth, the developing secondary ossification center formed in the center of this PTHrP-rich chondrocyte population. As the secondary ossification center developed, it segregated this population into two distinct PTHrP beta-gal+ subpopulations: a subarticular subpopulation immediately subjacent to articular chondrocytes and a proliferative chondrocyte subpopulation proximal to the chondrocyte columns in the growth plate. These discrete populations remained into adulthood. beta-gal activity was not identified in osteoblasts but was present in many periosteal sites. These included simple periosteum as well as fibrous tendon insertion sites of the so-called bony and periosteal types; the beta-gal-expressing cells in these sites were in the outer fibrous layer of the periosteum or its apparent equivalents at tendon insertion sites. Homozygous PTHrP-lacZ knockin mice had the expected chondrodysplastic phenotype and a much expanded region of proximal beta-gal activity in long bones, which appeared to reflect in large part the effects of feedback signaling by Indian hedgehog on proximal cell proliferation and PTHrP gene expression.

CONCLUSIONS

The PTHrP-lacZ mouse seems to provide a sensitive reporter system that may prove useful as a means of studying PTHrP gene expression.

Accelerated bone formation and increased osteoblast number contribute to the abnormal tooth germ development in parathyroid hormone-related protein knockout mice

Our previous study showed that tooth germs at late embryonic stage [later than embryonic day 17.5 (E17.5)] and neonatal homozygous parathyroid hormone-related protein (PTHrP)-knockout mice are compressed or penetrated by the surrounding alveolar bone tissue. In vivo and in vitro studies have shown that the development of the tooth germ proper is not disturbed, but insufficient alveolar bone resorption, due to the decreased number and hypofunction of osteoclasts, is the main cause of this abnormality. In addition to the insufficient alveolar bone resorption, progressive bone formation toward tooth germs was observed in homozygous mice, suggesting that accelerated bone formation also contributes to this abnormality. To further investigate this, homozygous mice at E14.0 and E15.5, when alveolar bone is forming, were used for histochemical and bone histomorphometric analyses. In contrast to the late embryonic stage, the alveolar bone did not yet compress developing tooth germs in homozygous mice on E14.0, but a larger amount of bone tissue was seen compared to wild-type littermates. Histomorphometric analysis of bone at E14.0 revealed that the osteoblast numbers and surfaces in the mandibles and in the bone collar of femora of homozygous mice were significantly higher than those of wild-type mice. However, unlike our previous study showing the osteoclast surface on E18.5 in homozygous mice to be significantly lower than that of wild-type mice, this study at E14.0 showed no significant difference between the two genotypes. To evaluate the amount of calcification around tooth germs, 3D images of mandibles were reconstructed from the calcein-labeled sections of the wild-type and mutant mice. Labeling was performed at E14.0, and the mice were sacrificed 1 h after the calcein injection to minimize the effect of bone resorption. Comparison of the 3D images revealed that the labeled surface was larger around developing tooth germs in homozygous mouse than in wild-type mouse. On day E15.5, osteoblasts approached the enamel organ of homozygous mice but this was not observed in wild-type mice. In this study, we report a systemic increase in osteoblast number and accelerated bone formation in homozygous PTHrP-knockout mice, both of which contribute to the abnormal tooth development.

Generation and analysis of Siah2 mutant mice

Siah proteins function as E3 ubiquitin ligase enzymes to target the degradation of diverse protein substrates. To characterize the physiological roles of Siah2, we have generated and analyzed Siah2 mutant mice. In contrast to Siah1a knockout mice, which are growth retarded and exhibit defects in spermatogenesis, Siah2 mutant mice are fertile and largely phenotypically normal. While previous studies implicate Siah2 in the regulation of TRAF2, Vav1, OBF-1, and DCC, we find that a variety of responses mediated by these proteins are unaffected by loss of Siah2. However, we have identified an expansion of myeloid progenitor cells in the bone marrow of Siah2 mutant mice. Consistent with this, we show that Siah2 mutant bone marrow produces more osteoclasts in vitro than wild-type bone marrow. The observation that combined Siah2 and Siah1a mutation causes embryonic and neonatal lethality demonstrates that the highly homologous Siah proteins have partially overlapping functions in vivo.

Development of a novel mouse osteoclast culture system including cells of mandibular body and erupting teeth

Osteoclasts are multinucleated cells with the specialized function of resorbing calcified tissues. These cells develop from hemopoietic cells of the monocyte-macrophage lineage with the support of osteoblasts/stromal cells. Tooth eruption is a vertical movement of teeth via creation of an eruption pathway in and through the alveolar bone. The precise cellular and molecular determinants of tooth eruption are not yet clear, and a cell culture system that can reproduce the activity of osteoclast formation during tooth eruption is expected to be a useful tool to clarify the mechanism of eruption pathway formation. To this end, mandibular bodies, including incisors and molars, were isolated from 9- to 11-day-old mice undergoing active tooth eruption. Primary cells were obtained from mandibular bodies by enzymatic digestion and cultured in alphaMEM containing 15% FBS without any cytokine or growth factor or hormone in the culture (AFT culture, for alveolar bone, dental follicle, and tooth). A progressive increase in the number of tartrate-resistant acid phosphatase-positive multinucleated osteoclastic cells was observed in AFT culture. The osteoclastic cells generated were immunopositive for cathepsin K and calcitonin receptor, and formed resorption pits when cultured on dentine slices. Parathyroid hormone-related protein (PTHrP), expressed by the enamel organ of tooth, is reported to be an essential factor in creation of the eruption pathway. To verify this point, cells were isolated from mandibular bodies from which all teeth and dental follicles had been removed and cultured similarly (A culture, for alveolar bone). Osteoclastic cells were not formed and PTHrP production was hardly detected in the medium of A culture, in contrast to the high level of PTHrP in AFT culture. Since our previous study demonstrated that neonatal homozygous PTHrP-knockout mice show impaired osteoclastogenesis around tooth germs, AFT culture was performed by using this sample to examine whether this culture system can reproduce the status of osteoclastogenesis observed in vivo. The result showed that none of the osteoclastic cells were generated from cells of homozygous mice. We here report a novel mouse osteoclast culture system that reproduces the activity of osteoclast formation around erupting teeth without addition of any cytokine or growth factor or hormone to the medium. Histological examination of various transgenic and mutant mice now offers valuable findings on studies of tooth eruption and the present culture system using these animals would be a powerful tool in clarifying the cellular and molecular mechanisms of eruption pathway formation.

Mandibular coronoid process in parathyroid hormone-related protein-deficient mice shows ectopic cartilage formation accompanied by abnormal bone modeling

Parathyroid hormone-related protein (PTHrP) null mutant mice were analyzed to investigate an additional role for PTHrP in cell differentiation. We found ectopic cartilage formation in the mandibular coronoid process in newborn mice. While many previous studies involving PTHrP gene knockout mouse have shown that the cartilage in various regions becomes smaller, this is the first report showing an "increase" of cartilage volume. Investigations of mandibular growth using normal mice indicated that coronoid secondary cartilage never formed from E 15 to d 4, but small amount of cartilage temporally formed at d 7, and this also applies to PTHrP-wild type mice. Therefore, PTHrP deficiency consequently advanced the secondary cartilage formation, which is a novel role of PTHrP in chondrocyte differentiation. In situ hybridization of matrix proteins showed that this coronoid cartilage had characteristics of the lower hypertrophic cell zone usually present at the site of endochondral bone formation and/or "chondroid bone" occasionally found in distraction osteogenesis. In addition, the coronoid process in the PTHrP-deficient mouse also showed abnormal expansion of bone marrow and an increase in the number of multinucleated osteoclasts, an indication of abnormal bone modeling. These results indicate that PTHrP is involved in bone modeling as well as in chondrocyte differentiation. In situ hybridization of matrix protein mRNAs in the abnormal mandibular condylar cartilage revealed that this cartilage was proportionally smaller, supporting previous immunohistochemical results.

The influence of parathyroid hormone-related protein (PTHrP) on tooth-germ development and osteoclastogenesis in alveolar bone of PTHrP-knock out and wild-type mice in vitro

In a previous study, it was shown that tooth germs of neonatal homozygous parathyroid hormone-related protein (PTHrP)-knockout mice are penetrated or compressed by the surrounding alveolar bone, suggesting an important role for PTHrP in the formation and activation of osteoclasts around growing tooth germs. In order to elucidate the role of PTHrP during the development of the tooth germ and related structures, mandibular explants containing cap stage tooth germs of embryonic day 14, homozygous mice were here cultured with or without surrounding alveolar bone. There was no difference in the number of tartrate-resistant acid phosphatase-positive multinucleated osteoclastic cells around the first molars of homozygous and wild-type mice. After 10 days of culture, osteoclastic cells were rarely present in explants from homozygous mice and penetration of alveolar bone into the dental papilla was observed. The decline in osteoclast number was partly restored by the addition of PTHrP to the culture. Tooth germs of both wild-type and homozygous mice cultured without alveolar bone developed well, with no apparent structural abnormality; dentine formation was evident after 10 days. These data suggest that PTHrP is not required for the development of the tooth germ proper but is indispensable in promoting the osteoclast formation required to accommodate that development.

Disturbed tooth development in parathyroid hormone-related protein (PTHrP)-gene knockout mice

Parathyroid hormone-related protein (PTHrP) is involved in epithelial-mesenchymal cell interactions during development of various tissues and organs. Tooth germ development is a classical model for this interaction. In tooth germs, PTHrP is expressed in the enamel organ (epithelial component), whereas its major receptor, the type I PTH/PTHrP receptor is expressed in cells of the alveolar bone and dental follicle (mesenchymal components). To clarify the role of PTHrP during fetal tooth germ development, PTHrP gene-knockout mice were used for histochemical and ultrastructural analysis. In wild-type mice, osteoclastic cells were aligned predominantly in the inner aspects of the alveolar bone surrounding the developing tooth germs throughout the late embryonic (after embryonic, 17.5 days) and neonatal animals examined. In contrast, osteoblasts were predominant in corresponding areas of fetal homozygous PTHrP-gene knockout mice with only occasional osteoclasts. In such areas, cell-free surfaces showing cement line-like tartrate-resistant acid phosphatase (TRAP) reactions were frequently observed. In neonatal homozygous mice, bone spicules were often shown to penetrate and/or compress the enamel organ and caused partial destruction of the tooth germs. Osteoclasts were few in number in the inner aspects of the alveolar bone, and had poorly developed ruffled border. No morphological abnormality was noted in cells of the tooth germs proper. On bone surfaces away from developing tooth germs, functional osteoclasts with structural features similar to those in wild-type mice were observed in homozygous mice. These observations suggest that PTHrP is required to maintain an appropriate spatiotemporal arrangement of bone cells and osteoclast function, which are necessary for the normal development of tooth germ and alveolar bone encasing the tooth germ. The observation also demonstrates that PTHrP deficiency affects the structure and function of osteoclasts exclusively those located in the vicinity of the growing tooth germ.

Parathyroid hormone-related protein is required for normal intramembranous bone development

It is well established that parathyroid hormone-related protein (PTHrP) regulates chondrocytic differentiation and endochondral bone formation. Besides its effect on cartilage, PTHrP and its major receptor (type I PTH/PTHrP receptor) have been found in osteoblasts, suggesting an important role of PTHrP during the process of intramembranous bone formation. To clarify this issue, we examined intramembranous ossification in homozygous PTHrP-knockout mice histologically. We also analyzed phenotypic markers of osteoblasts and osteoclasts in vitro and in vivo. A well-organized branching and anastomosing pattern was seen in the wild-type mice. In contrast, marked disorganization of the branching pattern of bone trabeculae and irregularly aligned osteoblasts were recognized in the mandible and in the bone collar of the femur of neonatal homozygous mutant mice. In situ hybridization showed that most of the osteoblasts along the bone surfaces of the wild-type mice and some of the irregularly aligned osteoblastic cells in the homozygous mice expressed osteocalcin. Alkaline phosphatase (ALP) activity and expression of osteopontin messenger RNA (mRNA) in primary osteoblastic cells did not show significant differences between cultures derived from the mixture of heterozygous mutant and wild-type mice (+/? mice) and those from homozygous mutant mice. However, both mRNA and protein levels of osteocalcin in the osteoblastic cells of homozygous mutant mice were lower than those of +/? mice, and exogenous PTHrP treatment corrected this suppression. Immunohistochemical localization of characteristic markers of osteoclasts and ruffled border formation did not differ between genotypes. Cocultures of calvarial osteoblastic cells and spleen cells of homozygous mutant mice generated an equivalent number of tartrate-resistant acid phosphatase-positive (TRAP+) mononuclear and multinucleated cells and of pit formation to that of +/? mice, suggesting that osteoclast differentiation is not impaired in the homozygous mutant mice. These results suggest that PTHrP is required not only for the regulation of cartilage formation but also for the normal intramembranous bone development.

Biosynthesis of proteoglycan in bone and cartilage of parathyroid hormone-related protein knockout mice

Proteoglycans are suggested to regulate cell adhesion, differentiation and mineralization of hard tissues. In vitro studies have shown that many humoral and local factors regulate proteoglycan synthesis. Among them, parathyroid hormone (PTH) and parathyroid hormone-related protein (PTHrP) have potent stimulating effects on proteoglycan synthesis. However, the exact role of PTHrP on the biosynthesis and metabolism of proteoglycans during skeletal development is not clear. To clarify this point, we examined bony and cartilaginous explants of newborn mice with disrupted PTHrP alleles. Ribs of homozygous PTHrP-knockout mice and wildtype littermates were dissected into bony and cartilaginous regions and metabolically labeled with [35S]sulfate in culture. Radiolabeled proteoglycans were analyzed by column chromatography. The elution profiles of [35S]-labeled proteoglycan from cartilaginous explants did not differ between homozygous PTHrP-knockout mice and wild-type littermates. However, the amount of labeled proteoglycan in homozygous PTHrP-knockout mice was only 4%-5% that of wild-type littermates. In contrast with cartilaginous explants, the amount of labeled proteoglycans in bony explants did not differ between the two genotypes. Interestingly, besides the common major peak (Kd = 0.10-0.16) observed in the bony explants of both genotypes, a minor peak (Kd = 0.42) was specifically present in homozygous PTHrP-knockout mice. This minor peak was earlier than that of free glycosaminoglycan (GAG) chains, suggesting that the core protein, but not GAG chain, was cleaved in the bony explants of homozygous PTHrP. These findings demonstrate a crucial nonredundant role of PTHrP in the regulation of proteoglycan synthesis and metabolism during skeletal development.

Mandibular deformities in parathyroid hormone-related protein (PTHrP) deficient mice: possible involvement of masseter muscle

Previous studies using parathyroid hormone-related protein (PTHrP) null mutant mice have indicated severe abnormalities in the endochondral ossification, suggesting that PTHrP affects chondrocyte differentiation. In this study, we found in newborn PTHrP-deficient mice some deformities in the mandible that is formed via intramembranous ossification. The mandibular ramus was bent downwards and a prominent bone crest to which the deep layer of masseter muscle was tendinously attached was observed in the mandibular body. Transmission electron microscopic studies showed that active bone formation was progressing along the tendon fibers of the masseter muscle. The examination of 3-D reconstruction models indicated that the mandibular ramus was bent at the site of muscle attachment, which was shifted in the direction of the muscle fibers. Muscle fiber type analysis using myosin ATPase staining showed that the masseter muscle in the newborn PTHrP-deficient mice contained numerous type 2B fibers, demonstrating premature maturation of this muscle. Based on these findings, we speculated that premature maturation of the masseter muscle leads, probably due to increased tensile forces, to accelerated bone crest formation and subsequent bending of the mandibular ramus. These results further suggest that PTHrP is involved in the regulation of muscle development in normal animals.

Parathyroid hormone-related protein regulates proliferation of condylar hypertrophic chondrocytes

The condylar cartilage, an important growth site in the mandible, shows characteristic modes of growth and differentiation, e.g., it shows delayed appearance in development relative to the limb bud cartilage, originates from the periosteum rather than from undifferentiated mesenchymal cells, and shows rapid differentiation into hypertrophic chondrocytes as opposed to the epiphyseal growth plate cartilage, which has resting and proliferative zones. Recently, attention has been focused on the role of parathyroid hormone-related protein (PTHrP) in modulating the proliferation and differentiation of chondrocytes. To investigate further the characteristic modes of growth and differentiation of this cartilage, we used mice with a disrupted PTHrP allele. Immunolocalization of type X collagen, the extracellular matrix specifically expressed by hypertrophic chondrocytes, was greatly reduced in the condylar cartilage of homozygous PTHrP-knockout mice compared with wild-type mice. In contrast, immunolocalization of type X collagen of the tibial cartilage did not differ. In wild-type mice, proliferative chondrocytes were mainly located in both the flattened cell layer and hypertrophic cell layer of the condylar cartilage, but were limited to the proliferative zone of the tibial cartilage. The number of proliferative chondrocytes was greatly reduced in both cartilages of homozygous PTHrP-knockout mice. Moreover, apoptotic chondrocytes were scarcely observed in the condylar hypertrophic cell layer, whereas a number of apoptotic chondrocytes were found in the tibial hypertrophic zone. Expression of the type I PTH/PTHrP receptor was localized in the flattened cell layer and hypertrophic cell layer of the condylar cartilage, but was absent from the tibial hypertrophic chondrocytes. It is therefore concluded that, unlike tibial hypertrophic chondrocytes, condylar hypertrophic chondrocytes have proliferative activity in the late embryonic stage, and PTHrP plays a pivotal role in regulating the proliferative capacity and differentiation of these cells.

Differential responses to parathyroid hormone-related protein (PTHrP) deficiency in the various craniofacial cartilages

PTHrP null mutant mice exhibit skeletal abnormalities both in the craniofacial region and limbs. In the growth plate cartilage of the null mutant, a diminished number of proliferating chondrocytes and accelerated chondrocytic differentiation are observed. In order to examine the effect of PTHrP deficiency on the craniofacial morphology and highlight the differential feature of the composing cartilages, we examined the various cartilages in the craniofacial region of neonatal PTHrP deficient mice. The major part of the cartilaginous anterior cranial base appeared to be normal in the homozygous PTHrP deficient mice. However, acceleration of chondrocytic differentiation and endochondral bone formation was observed in the posterior part of the anterior cranial base and in the cranial base synchondroses. Ectopic bone formation was observed in the soft tissue-running mid-portion of the Meckel's cartilage, where the cartilage degenerates and converts to ligament in the course of normal development. The zonal structure of the mandibular condylar cartilage was scarcely affected, but the whole condyle was reduced in size. These results suggest the effect of PTHrP deficiency varies widely between the craniofacial cartilages, according to the differential features of each cartilage.

Mice without a functional relaxin gene are unable to deliver milk to their pups

We have used gene targeting to generate relaxin (rlx)-deficient mice. The majority (15 of 17) of homozygous (rlx-/-) mice are fertile and produce normal litters. However their mammary development is deficient; pups are unable to suckle and die within 24 h of birth unless cross-fostered to a wild-type (rlx+/+) foster mother. The nipples of rlx-/- animals do not enlarge significantly during pregnancy, and their histology retains the appearance of the virgin state. Breast parenchyma is somewhat underdeveloped at term even though milk is produced. Mammary ducts become grossly dilated in these animals. Heterozygous (rlx+/-) mice lactate normally. The interpubic ligament does not relax during pregnancy in rlx-/- mice. Plasma osmolality during late gestation was significantly higher (P < 0.001) in rlx-/- mice than in wild-type controls.

Homeosis and intestinal tumours in Cdx2 mutant mice

In Drosophila, disturbing the expression of the homeobox gene caudal causes a severe disruption in body segmentation and global body patterning. There are three mouse homologues of Drosophila caudal: Cdx1 (ref. 2), Cdx2 (ref. 3) and Cdx4 (ref. 4). We have generated a null mutation of murine Cdx2 by homologous recombination. Cdx2 homozygote null mutants die between 3.5 and 5.5 days post coitum (d.p.c.). Cdx2 heterozygote mutants exhibit a variable phenotype, with many showing tail abnormalities or stunted growth. Skeletal analysis demonstrates a homeotic shift of vertebrae and compatible malformations of the ribs. Within the first three months of life, 90% of Cdx2 heterozygotes develop multiple intestinal adenomatous polyps, particularly in the proximal colon. These polyps occasionally contain areas of true metaplasia. In contrast to the surrounding intestinal epithelium, the neoplastic cells do not express Cdx2 from the remaining allele. These results suggest that Cdx2 mutation is the primary event in the genesis of some intestinal tumours.

Mutation in Sos1 dominantly enhances a weak allele of the EGFR, demonstrating a requirement for Sos1 in EGFR signaling and development

We have investigated the role of the mammalian Son of sevenless 1 (Sos1) protein in growth factor signaling in vivo by generating mice and cell lines that lacked the Sos1 protein. Homozygous null embryos were smaller than normal, died mid-gestation with cardiovascular and yolk sac defects, and their fibroblasts showed reduced mitogen-activated protein kinase activation in response to epidermal growth factor (EGF). An intercross of mice mutant for Sos1 and the EGF receptor (EGFR) demonstrated that a heterozygous mutation in Sos1 dominantly enhanced the phenotype of a weak allele of the EGFR allele (wa-2). These animals had distinctive eye defects that closely resembled those seen in mice that were null for the EGFR or its ligand, TGF alpha. Our findings provide the first demonstration of a functional requirement for Sos1 in growth factor signaling in vivo. They also show that the genetic test of enhancement of weak receptor allele by heterozygous mutation in one component represents a powerful tool for analyzing the ras pathway in mammals.

Cloning and expression analysis of a cytochrome P-450(11 beta) cDNA in sheep

A full length ovine steroid 11 beta-hydroxylase (cytochrome P-450(11 beta)) cDNA clone from a sheep adrenal cortex cDNA library was isolated. Sequence analysis indicates that this cDNA clone resembles bovine P-450(11 beta) cDNA (95% nucleotide sequence homology) more closely than rat P-450(11 beta) cDNA (69% nucleotide sequence homology). Although the levels of nucleotide sequence homology of this cDNA clone to the rat P-450(11 beta) cDNA and the rat P-450aldo cDNA are similar, the putative amino acid sequence shows a closer resemblance to rat P-450aldo protein. Northern blot analysis shows that there are three sizes of transcript and they are expressed throughout the adrenal cortex.

Molecular cloning and characterization of the cyclic AMP-responsive ovine CYP11A1 (cholesterol side-chain cleavage) gene promoter: DNase 1 protection of conserved consensus elements

DNA elements governing transcription of the ovine cytochrome P-450 side-chain cleavage (CYP11A1) gene were investigated. Three overlapping genomic clones for the ovine CYP11A1 gene were isolated and characterized. The transcriptional start site was located 51 nucleotides upstream from the initiating methionine. Gene transfer experiments were conducted in murine adrenocortical Y1 cells and human choriocarcinoma JEG-3 cells using chloramphenicol acetyltransferase reporter gene constructs containing promoter fragments from -2700 to -177 bp. The results demonstrate that DNA elements sufficient to convey a basal level of expression and cyclic AMP (cAMP) responsiveness lie within 177 bp of the transcriptional start, although the possibility that additional regulatory elements reside outside this 177 bp has not been excluded. The ovine 5' flanking sequence demonstrated 92% homology with the bovine sequence, extending over the entire fragment. In contrast, only four significant regions of conservation between the ovine, murine, rat and human CYP11A1 promoters were found. These regions are positioned within 200 bp upstream of the transcriptional start site. DNase 1 footprinting was performed to identify DNA elements able to bind nuclear proteins. Primary adrenocortical and placental tissues from sheep were used as the source of nuclear extracts to detect DNA-protein interactions relevant to CYP11A1 gene expression in vivo. Five regions of protection were detected in the first -634 bp of the ovine CYP11A1 promoter. Three of these elements corresponded to the regions which are well-conserved between species. The other two elements resembled activating protein-1 (AP-1) and AP-4 sites and overlapping AP-2/Sp1 sites, and are conserved in the bovine gene but not in other species. Nuclear protein extracts from adrenals of sheep with different serum ACTH levels (i.e. ACTH-treated, dexamethasone-treated and untreated sheep) protected similar regions of the ovine CYP11A1 promoter fragment. Similarly, the regions protected did not differ when nuclear protein from JEG-3 cells treated with cAMP was compared with that of untreated JEG-3 cells. These results suggest that induction of CYP11A1 gene transcription by ACTH in the ovine adrenal and by cAMP in JEG-3 cells in culture is not mediated by changes in binding of the proteins that interact directly with these footprinted elements. The elements footprinted by extracts from primary ovine tissue lie within the 177 bp sufficient for cAMP-regulated expression. The correspondence of these elements either to regions conserved between species or to known consensus binding sites suggests that these sequences are cis elements involved in regulating transcription of the ovine CYP11A1 gene in vivo.

The structure and activity of two cytochrome P450c21 proteins encoded in the ovine adrenal cortex

The steroidogenic enzyme cytochrome P450c21 (CYP21A1) is synthesized in the adrenal cortex and is essential for cortisol and aldosterone production. We have studied the structure and activity of ovine P450c21 proteins by analysis and expression of the corresponding cDNAs. Two P450c21 mRNAs (2.2 and 1.7 kilobases) were detected in ovine adrenal RNA and corresponded to two types of P450c21 cDNA clones that differed in their 3' region. One clone encoded a protein similar in structure to bovine, murine, and human P450c21 proteins. The other clone contained a 3' deletion of about 500 nucleotides and encoded a P450c21 protein that was truncated by 18 residues at the carboxyl terminus. The boundaries of this deletion suggested that an additional splicing event was responsible for the shortened mRNA sequence. Detailed Southern analysis of ovine genomic DNA indicates that the two mRNAs are derived from one gene even though two P450c21 genes are present in the ovine genome. The activities of the two P450c21 proteins were determined by expressing the respective cDNA clones in COS cells. The complete P450c21 protein was an efficient catalyst of 21-hydroxylation reactions, whereas no 21-hydroxylation activity was detected in cells containing the P450c21 protein with the carboxyl-terminal deletion.

Steroid hydroxylase gene expression in the ovine fetal adrenal gland following ACTH infusion

Between 90 and 120 days of gestation (term = 147 +/- 5), when plasma cortisol concentrations in the fetus are at a minimum, levels of mRNA encoding the steroidogenic enzymes 17 alpha-hydroxylase (P-450(17 alpha] and cholesterol side-chain cleavage (P-450scc) are also very low. Over the following 30 days, P-450(17 alpha) and P-450scc gene expression increases concurrent with increasing fetal cortisol concentration. The hypothesis tested in this study was that cortisol biosynthesis is minimal in the period 90-120 days because of insufficient ACTH. Fetuses were cannulated between 98-102 days of gestation. Following recovery, 7 fetuses received 24-h ACTH infusions (12 micrograms/24 h) and 5 fetuses received 24-h vehicle infusions; 4 ACTH-infused and 4-vehicle-infused fetuses were then sacrificed immediately after cessation of the infusion. The other fetuses were left in utero for 3 days prior to sacrifice. Fetal blood samples were analysed for ACTH and cortisol and the adrenals processed for hybridization histochemistry and Northern blot analysis. ACTH, but not vehicle, induced significant increases in the width of the adrenal cortex and in the levels of P-450(17 alpha) and P-450scc mRNA. Concurrently, fetal plasma ACTH and cortisol concentrations also increased significantly. In adrenals from fetuses left in utero for 3 days after cessation of the ACTH infusion, P-450(17 alpha) and P-450scc mRNA levels returned to control levels. Plasma ACTH and cortisol levels also approximated basal values. P-450c21 mRNA levels did not vary significantly at any time with the treatments.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential expression of inhibin alpha and beta A subunit genes in rat and mouse ovarian follicles during pregnancy

Relative levels of rat ovarian alpha inhibin (alpha I) and beta A inhibin (beta AI) mRNAs were measured during pregnancy by dot-blot hybridization of ovarian poly(A+) RNA. Follicular patterns of alpha I and beta AI expression in contralateral ovaries from the same rats were also studied by hybridization histochemistry. Oligodeoxynucleotide probes specific for porcine alpha I and beta AI were synthesized, 32P end-labelled and used as hybridization probes on dot-blots of ovarian RNA and frozen sections of ovarian tissue from pregnant rats. During pregnancy, levels of alpha I and beta AI mRNAs remained fairly constant from day 7 after mating until parturition and then fell within 16 h post partum. In all ovaries observed, expression of inhibin genes was located in granulosa cells of healthy antral follicles. In general, the strongest signals for alpha I and beta AI mRNAs were obtained in large follicles, with weaker signals in smaller follicles. Follicular patterns of alpha I and beta AI expression during pregnancy were often dissimilar when alpha I and beta AI were compared over a range of follicles. Considerable alpha I mRNA was detectable in some follicles in which beta AI was reduced or undetectable, despite strong signals for both alpha I and beta AI in an adjacent follicle. Essentially, alpha I mRNA levels were relatively consistent between groups of follicles, whereas beta AI levels varied considerably. beta AI mRNA was never observed in a follicle in the absence of alpha I mRNA, indicating that activin production in any follicle occurs in the presence of alpha I mRNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Structure of rhesus monkey relaxin predicted by analysis of the single-copy rhesus monkey relaxin gene

The gene encoding rhesus monkey relaxin has been investigated. A cDNA library was prepared using corpus luteal RNA from a pregnant rhesus monkey, cDNA clones encoding relaxin were isolated and the nucleotide sequence was determined. The amino acid sequence of rhesus monkey preprorelaxin, predicted from the cDNA, demonstrates that the sequence has not been strongly conserved when compared with that of man, although features characteristic of the relaxin molecule have been maintained. This structural information will allow production of rhesus monkey relaxin, leading to studies investigating the bioactivity of relaxin in a homologous primate system. Southern blot analysis indicated that there is only one relaxin gene in the rhesus monkey and baboon genomes. In this respect these primate genomes are different from the human genome which contains two relaxin genes.

Tissue distribution and levels of gene expression of three steroid hydroxylases in ovine fetal adrenal glands

Northern blotting and hybridization histochemistry were used to evaluate the ontogeny and cellular distribution of the mRNAs of the cytochrome P-450 enzymes: cholesterol side-chain cleavage (P-450scc), 17 alpha-hydroxylase (P-450(17 alpha] and 21-hydroxylase (P-450c21) in 40 ovine fetal adrenals from 42 days of gestation until term (151 days). The genes for P-450(17 alpha) and P-450scc were expressed strongly in tissue from young (40-60 days) and old fetuses (120 days to term), but to a very minor degree in 90-120 day fetuses. P-450c21 showed a steady increase throughout gestation. In the morphologically immature an unzoned adrenal of the 40-50 day fetus there was some differentiation in gene expression, all cells containing P-450scc and P-450c21 but a few lacking P-450(17 alpha). Once morphological zonation had occurred (80 days), P-450(17 alpha) was confined to the fasciculata. After 120 days there was a radial maturation pattern of the fasciculata cells morphologically, adult-type cells first appearing at the medullary border. However, P-450(17 alpha) and P-450scc mRNAs were equally well expressed in all sections of the fasciculata. The conclusions were: 1) the previously demonstrated triphasic cortisol biosynthetic capacity of ovine fetal adrenals was correlated with the presence, absence, and reappearance of mRNAs P-450(17 alpha) and P-450scc; 2) morphological appearance of fetal adrenocortical cells and expression of three major steroidogenic enzyme genes were not correlated.

Alpha-inhibin gene expression occurs in the ovine adrenal cortex, and is regulated by adrenocorticotropin

Inhibin is a glycoprotein hormone composed of two nonidentical subunits. It is produced by the ovary and testis and plays a vital role in gonadal function by inhibiting the secretion of FSH. More recently, additional activities associated with inhibin peptides have been identified. Inhibin heterodimers (alpha-beta) are reported to act directly on ovarian granulosa cells and inhibit estrogen production induced by FSH. Furthermore, homodimers of beta-inhibin subunits stimulate the secretion of FSH, an activity that is directly opposite to that of inhibin. Each of these inhibin-related activities are concerned with the hypothalamic-pituitary-gonadal axis. We have investigated further the complexity of inhibin activity by determining whether inhibin genes are expressed in nongonadal tissue. RNA hybridization experiments demonstrate that the alpha-inhibin gene is expressed in the sheep adrenal cortex and hybridization histochemistry shows that this gene is expressed in each of the functional zones within the cortex. Dot blot analysis showed that the level of alpha mRNA within the adrenal is influenced by ACTH, one of the major regulators of adrenal cortex function. These observations imply that there are inhibin-related peptides not directly associated with the gonads. beta-inhibin gene expression was not clearly detected in the adrenal and we conclude that if expression occurs then it does so at extremely low levels.

Retinogeniculate patterns in diprotodont marsupials

The pattern of retinogeniculate connections has been examined in a range of diprotodont marsupials, including wallabies, possums, forest wombat and koala. The lateral geniculate nucleus (LGd) in most species has alternating bands of ipsilateral and contralateral retinal terminal fields, with considerable interspecific variability. The number of terminal bands of retinogeniculate input varies from eight to eleven in most species, with little binocular overlap. By contrast in one species, the feather-tailed glider, the most significant feature of LGd organisation is binocular overlap. No relationship is apparent between LGd organisation and the life-style of the animals.