Interparietal Bone Research Articles

Theoretical model of impact mitigation mechanisms inherent to the North American bison skull

ABSTRACT North American bison (Bovidae: Bison bison) incur blunt impacts to the interparietal and frontal bones when they engage in head-to-head fights. To investigate the impact mitigation of these bones, a finite element analysis (FEA) of the skull under loading conditions was performed. Based on anatomical and histological studies, the interparietal and frontal bones are both comprised of a combination of haversian and plexiform bone and are both underlain by bony septa. Additionally, the interparietal bone is thicker than the frontal bone. Data regarding the mechanical properties of bison bone are scarce, but the results of a phylogenetic analysis infer that the material properties of the closely related domestic cow bone are a suitable proxy for use in the FEA. Results of the FEA suggest that the thickness of the interparietal bone in conjunction with the bony septa may prevent fracture stresses by helping to absorb and disperse the blunt impact energy throughout the skull. Monotonic stress levels of 294 MPa, which are below the compressive strength of bone were exhibited in the simulated bison head impacts indicating no fracture of the bones.

Cranial asymmetry in odontocetes: a facilitator of sonic exploration?

Directional cranial asymmetry is an intriguing condition that has evolved in all odontocetes which has mostly been associated with sound production for echolocation. In this study, we investigated how cranial asymmetry varies across odontocete species both in terms of quality (i.e., shape), and quantity (magnitude of deviation from symmetry). We investigated 72 species across all ten families of Odontoceti using two-dimensional geometric morphometrics. The average asymmetric shape was largely consistent across odontocetes – the rostral tip, maxillae, antorbital notches and braincase, as well as the suture crest between the frontal and interparietal bones were displaced to the right, whereas the nasal septum and premaxillae showed leftward shifts, in concert with an enlargement of the right premaxilla and maxilla. A clear phylogenetic signal related to asymmetric shape variation was identified across odontocetes using squared-change parsimony. The magnitude of asymmetry was widely variable across Odontoceti, with greatest asymmetry in Kogiidae, Monodontidae and Globicephalinae, followed by Physeteridae, Platanistidae and Lipotidae, while the asymmetry was lowest in Lissodelphininae, Phocoenidae, Iniidae and Pontoporiidae. Ziphiidae presented a wide spectrum of asymmetry. Generalized linear models explaining magnitude of asymmetry found associations with click source level while accounting for cranial size. Using phylogenetic generalized least squares, we reconfirm that source level and centroid size significantly predict the level of cranial asymmetry, with more asymmetric marine taxa generally consisting of bigger species emitting higher output sonar signal, i.e. louder sounds. Both characteristics theoretically support foraging at depth, the former by allowing extended diving and the latter being adaptive for prey detection at longer distances. Thus, cranial asymmetry seems to be an evolutionary pathway that allows odontocetes to devote more space for sound-generating structures associated with echolocation and thus increases biosonar search range and foraging efficiency beyond simple phylogenetic scaling predictions.

Localized, time-dependent responses of rat cranial bone to repeated mild traumatic brain injuries

While it is well-established that bone responds dynamically to mechanical loading, the effects of mild traumatic brain injury (mTBI) on cranial bone composition are unclear. We hypothesized that repeated mTBI (rmTBI) would change the microstructure of cranial bones, without gross skull fractures. To address this, young adult female Piebald Viral Glaxo rats received sham, 1×, 2× or 3× closed-head mTBIs delivered at 24 h intervals, using a weight-drop device custom-built for reproducible impact. Skull bones were collected at 2 or 10 weeks after the final injury/sham procedure, imaged by micro computed tomography and analyzed at predetermined regions of interest. In the interparietal bone, proximal to the injury site, modest increases in bone thickness were observed at 2 weeks, particularly following 2× and 3× mTBI. By 10 weeks, 2× mTBI induced a robust increase in the volume and thickness of the interparietal bone, alongside a corresponding decrease in the volume of marrow cavities in the diploë region. In contrast, neither parietal nor frontal skull samples were affected by rmTBI. Our findings demonstrate time- and location-dependent effects of rmTBI on cranial bone structure, highlighting a need to consider microstructural alterations to cranial bone when assessing the consequences of rmTBI.

Comparative morphological aspect of the study of bones of domestic and wild animals

At present, there is not enough information in the available literature about the anatomical features of the skull bones of various animal species, which is relevant when conducting forensic veterinary and medical examinations. Understanding of the structure of living organisms is impossible without anatomical preparations; it is necessary to clearly understand the place and position of each organ, to know all the options for anatomical relationships with neighboring organs. Knowledge of topographic anatomy is extremely important for the practitioner, it is necessary for successful diagnosis and subsequent treatment. The purpose of this work is to compare the bones of the skull of a cat, rabbit and hare, as well as to study their structure and morphometric parameters.Objects and methods. The objects of the study were the skulls of domestic and wild animals: a domestic outbred cat, a rabbit of the Gray giant breed, a brown hare. The work was carried out in several stages: digestion with the addition of sodium bicarbonate, cleaning, bleaching with a 3% hydrogen peroxide solution, drying, followed by morphometric measurement and visual comparison.Results. In a cat, the premaxillary bone and supraorbital process are absent, the hook of the pterygoid bone is long and rounded inwards. In rabbit and hare skulls, the anterior and posterior supraorbital processes are present on the frontal bone, and the hook of the pterygoid bone is short, sharp, and straight. The interparietal bone of the hare merged with the occipital, while in the rabbit and cat it exists as an independent bone. The information provided will greatly facilitate the conduct of a veterinary forensic examination in the investigation of crimes related to poaching.

Prenatal and early post-natal development of the skull in Nigerian breeds of sheep: a gross anatomical study

The aim of this study was to bridge the gap of information on the gross morphology of the skull of sheep foetuses. A total of 240 samples consisting of fetal and day-old Balami, Uda and Yankasa breeds were used; the skulls were prepared using chemical maceration technique. In the 1st trimester, no visible ossifications were observed on the skull. In the 2nd trimester, ossification of the frontal, parietal, occipital and basisphenoid bones were observed. The nasal bones were ossified, but concaved in Balami and flat in Uda and Yankasa. In the 3rd trimester, an interparietal bone developed between the parietal and occipital bones. The paracondyloid processes, occipital squamous, and the external occipital protuberance were developed in the 3rd trimester. The interparietal bone appeared paired in Yankasa but unpaired in Balami and Uda, which developed into a paired bone in the day-old. In the day-old, the orbital walls were completely fused except in the Uda; the formation of the cornual process began; the presphenoid of the Yankasa was developed. It was concluded that grossly, ossification was observed in the 2nd trimester and it began with the neurocranial bones, however, in the 2nd trimester, the skull was partly soft and pliable and the foramina were rudimentary. In the 3rd trimester, the skull bones were hard and osseous. All the bones on the dorsal surfaces of the skull were membranous whereas some of the bones of the ventral surface were cartilaginous in origin.

Micro-computed tomography assessment of bone structure in aging mice

High-resolution computed tomography (CT) is widely used to assess bone structure under physiological and pathological conditions. Although the analytic protocols and parameters for micro-CT (μCT) analyses in mice are standardized for long bones, vertebrae, and the palms in aging mice, they have not yet been established for craniofacial bones. In this study, we conducted a morphometric assessment of craniofacial bones, in comparison with long bones, in aging mice. Although age-related changes were observed in the microarchitecture of the femur, tibia, vertebra, and basisphenoid bone, and were more pronounced in females than in males, the microarchitecture of both the interparietal bone and body of the mandible, which develop by intramembranous ossification, was less affected by age and sex. By contrast, the condyle of the mandible was more affected by aging in males compared to females. Taken together, our results indicate that mouse craniofacial bones are uniquely affected by age and sex.

Evolution and Development of the Interparietal in Dolphins and Other Toothed Whales (Odontocetes)

Mammal skulls of diverse shapes and sizes exhibit a skull roof composed of the same bones with a similar topological arrangement: bilateral frontal and parietal bones meet at the midline, and in many cases, an interparietal bone lies posterior to the parietals. Despite this conserved skull roof arrangement, the interparietal has been a puzzling bone in comparative embryology and evolutionary morphology due to its mixed developmental origins and its variable patterns of fusion with neighboring bones, resulting in mixed reports of presence and absence in different taxa. The skull roof of dolphins, in contrast to other mammals, features a prominent interparietal that separates the parietal bones so that the parietals do not meet at the midline. While this unusual configuration has been described in individual specimens, the evolutionary developmental patterns that led to the dolphin arrangement are largely unknown. To understand how this unique arrangement arose, we surveyed presence, absence, morphology, position, and developmental origins among early odontocete fossils and extant odontocete fetuses. Among extant odontocetes, delphinoids all have multi‐element interparietal bones: one comprising the traditional “interparietal” between the paired parietal bones, and two that fuse posteriorly to the supraoccipital. However, extant physeteroids lack an identifiable interparietal, possibly resulting from the fusion of interparietal elements to the supraoccipital during early development. Thus, in physeteroids, the parietals meet at the midline as in other mammals. Olympicetus, an Oligocene stem odontocete, exhibits several well‐preserved multi‐element interparietals, including one underneath and at the midline of its paired parietal bones. However, other Oligocene stem odontocetes from South Carolina revealed no identifiable interparietal at multiple growth stages, which may have resulted from fusion of interparietal elements to other skull bones. These new data suggest that fusion patterns of the multiple elements of the interparietal are highly variable among odontocetes and support the hypothesis that the presence of a large interparietal separating the parietals is a uniquely delphinoid feature.

Prenatal and early post-natal development of the skull in Nigerian breeds of sheep: a gross anatomical study

The aim of this study was to bridge the gap of information on the gross morphology of the skull of sheep foetuses. A total of 240 samples consisting of fetal and day-old Balami, Uda and Yankasa breeds were used; the skulls were prepared using chemical maceration technique. In the 1st trimester, no visible ossifications were observed on the skull. In the 2nd trimester, ossification of the frontal, parietal, occipital and basisphenoid bones were observed. The nasal bones were ossified, but concaved in Balami and flat in Uda and Yankasa. In the 3rd trimester, an interparietal bone developed between the parietal and occipital bones. The paracondyloid processes, occipital squamous, and the external occipital protuberance were developed in the 3rd trimester. The interparietal bone appeared paired in Yankasa but unpaired in Balami and Uda, which developed into a paired bone in the day-old. In the day-old, the orbital walls were completely fused except in the Uda; the formation of the cornual process began; the presphenoid of the Yankasa was developed. It was concluded that grossly, ossification was observed in the 2nd trimester and it began with the neurocranial bones, however, in the 2nd trimester, the skull was partly soft and pliable and the foramina were rudimentary. In the 3rd trimester, the skull bones were hard and osseous. All the bones on the dorsal surfaces of the skull were membranous whereas some of the bones of the ventral surface were cartilaginous in origin.

Congenital skeletal malformations induced by lambda-cyhalothrin, dibenzalacetone and heptanone derivatives in embryos of albino mice

Background: Insecticides such as lambda-cyhalothrin(LCT), dibenzalacetone (DBA) and heptanone HD are teratogenic substances. Skeleton is one of the organs sensitive to teratogens during the period of organogenesis. Material and methods:This study was conducted on fifty adult female albino mice, divided randomly into four groups: Group I (control group, n= 5 received corn oil orally in adose of 10 mg /kg body weight), group II (LCT group, n=10 received LCT (nano 8%)10, 20 mg /kg body weight for each subgroup), group III (DBA group, n=20, received DBA (main) 10, 20 mg /kg body weight and DBA (nano 8%)) 10,20mg /kg body weight for each subgroup) and group IV (HD group, n=15, received HD (main) 10 mg /kg body weight and HD (nano 8%)) 10,50mg /kg body weight for each subgroup),The calculated treatment dissolved in 1 ml of corn oil by orogastric tube was given to the pregnant mice during the first week of pregnancy (1st, 3rd and 5th day).The delivered live and dead pups were examined externally, then double stained and prepared for skeletal examination by dissecting microscope. Results: All experimental groups showed various anomalies that can be categorized as the following: 1) presence of dead pups and resorption sites 2) macroscopic anomalies in the form of anencephaly, extended forelimb, cranioshisis, macroglossia, lowset ears, lage eye bulge, half body, amelia, internal rotation of forelimb and encephalocele. 3) skeletal anomalies by double staining of fetal skeleton showed incomplete ossification of nasal and interparietal bones, open arch of atlas, incomplete ossification of vertebrae, supernumerary ribs, wavy ribs, incomplete ossification of ribs and sternebrae, incomplete ossification of sternum, incomplete ossification of 5th metacarpal and terminal phalangal bones and incomplete ossification of tarsal , and phalangal bones. Conclusion: Lambda-cyhalothrin, dibenzalacetone and derivatives of heptanone result in numbers of congenital gross and skeletal abnormalities that indicate their teratogenic effect. KEY WORDS: Lambada, Congenital, Skeletal, Dibenzalacetone, Heptanone, Teratogenic.

Evcil Ördek (Anas Domesticus) ve Evcil Kaz (Anser Domesticus) Neurocranium’u Üzerinde Karşılaştırmalı Makro-Anatomik İncelemeler

The study was carried out to examine the neurocranium bones of domestic duck and domestic goose and to investigate the differences in both species. In the study, ten domestic geese (five females-five males) and domestic duck skulls (five females-five males) were used as materials. The domestic duck and domestic goose skulls were cleaned after they were properly boiled. The neurocranium; It was observed that it consisted of occipital, sphenoid, parietal, frontal and temporal bones. In the domestic duck and domestic goose; foramen magnum was determined to be in vertical and nuchal position. It was observed that the parietal bone formed the caudolateral part of the skull ceiling and was convex in the both species. It was determined that frontal bone in domestic goose is wider than domestic duck. It was observed that there were two holes in fontanella in both species and it was triangular in shape of sphenoid bone. It was seen that pars nasalis developed very well in domestic duck and domestic goose. It was determined that interparietal bone wasn’t present in both materials and ethmoidal bone was within the scope of viscerocranium bones. As a result; It was concluded that there are some differences between the bones that form the domestic duck and domestic goose neurocranium and these differences can be used in taxonomy.

Skeletal congenital abnormalities induced by nickel chloride hexahydrate on Balb/C albino mice embryos during organogenetic period

Nickel is an essential metal, and its compounds are widely used in industry and commerce. The development of industrialization has led to increased emission of nickel into environment causing teratogenesis in the developing embryos. This study aimed to investigate the toxic and teratogenic effects of nickel on Balb/C albino mice embryos during organogenetic period. This study was carried out on forty pregnant female albino mice; they were randomly divided into four equal groups: group I (control group) received distilled water; groups II, III, and IV (experimental groups): each group contains ten mice received 46.125 mg, 92.25 mg, and 184 mg Ni/kg body weight, per day, respectively, by orogastric tube for successive 8 days started from the 6th gestational day. The extracted lived fetuses were examined externally then double-stained and prepared for skeletal examination by dissecting microscope. The numbers of live-birth pups decreased significantly (p value for comparing between control and each other group, statistically significant at p ≤ 0.05). But there was significant increase in resorption sites in all nickel-treated groups compared to control group. Total number of resorption sites in all nickel-treated groups is 28: 15 resorption sites are present at left horn and 13 in the right horn. At the same time, there was significant increase in stillbirth fetuses in group IV. Double-stained fetal skeleton showed incomplete ossification of skull bones, unossified interparietal bone, open arch of atlas, incomplete ossification of vertebrae, supernumerary lumbar rib, incomplete ossification of ribs and sternebrae, incomplete ossification of bones of forelimb, incomplete ossification of bones of hindlimb, unossified carpals, metacarpals, tarsals, metatarsals, and phalanges in nickel-treated groups, compared to control group. Nickel results in number of skeletal congenital abnormalities indicating its teratogenic effect.

Inconstant bones of the human skulls from scythians grave field near Kolomak village

Summary: The research of the features of variant anatomy, as an integral part of paleoanthropological exploration, is an extremely important source of additional information about the anatomical structure of humans. Рatterns of variability and frequency distribution of discrete variational features in variant anatomy remain important. Cranioscopic variational (or non-metric) features - anatomical variations in the skeleton structure, registered according to the “presence-absence” principle, are an important source of information in studying the origin and ethnogenetic relationships of paleopopulations. These features include inconstant (additional) skull bones. By modern classification, there are three types of inconstant bones of the human skull: wormian (sutural) bones, fontanelle bones and insular bones. They have various causes: genetic factors, chronic high intracranial pressure, skull deformation, disturbances of the skull symmetry, different pathological processes, etc. The purpose of the work was to research the variant anatomy of inconstant bones of the human skull. The objective to research is the variant anatomy of inconstant skull bones of the human on the anthropological materials from the Scythian grave field. It located near Kolomak village in the Kharkiv region and dates back to IX – IV century BC. The 88 skulls of adult persons has been researched. The inconstant additional bones of skull were present in the structures of 16 skulls out of 88 (18.1%). Results. The sutural (wormian) bones were present in 12 skulls (13.6%), fontanelle bones – in 6 skulls (6.8%), insular bones were absent. In the anatomical structures of 10 skulls (11.4%) were only wormian bones, in 4 skulls (4.5%) were only fontanelle bones, in the structures of 2 skulls (2.3%) were combination of sutural and fontanelle additional bones. Often the inconstant bones were located in several sutures at the same time. The most common sutural bones were lambdoid suture bones - 9 skulls (10.2%). The inconstant bones of the coronal suture and sagittal suture were found in 2 skulls (2.3%). The additional bones of the occipital-mastoid, parietal-mastoid and squamosal sutures were absent on the examined osteological materials. The fontanelle bones most often located at the place of the occipital fontanellele and they were present in 4 skulls (4.5%). The additional fontanelle bones of the mastoid fontanellele were found in 2 skulls (2.3%). The frontal fontanelle bone was in 1 skull (1.1%). The additional fontanelle bones of the sphenoid fontanellele and interparietal bones were not found in the researched skulls. Conclusion. It is interesting to consider the case of combination in one skull a large inconstant bone of the sagittal suture with complete metopic (frontal) suture and occipital bone of sufficiently large size. The results of the research expanded and updated the existing data on the variant anatomy of inconstant cranial bones. Also, the results obtained maybe required in the further research of individual variability in the structure of the human’s skull.

English

English

Développement et croissance de la voûte du crâne

The vault of the skull is a region of the neurocranium formed by a process of membranous ossification. It consists of several bones: frontal bone, parietal bone, squamous part of the temporal bone, lamina ascendens of the sphenoid, and interparietal bone. The embryological origin of the bones of the skull vault is still the subject of controversy. This can be explained by the different animal models used for these purposes, but also by the various techniques applied to this problem. At all events, it seems that the cells of the neural crest generate some of the bones of the vault and that the others are derived from the mesoderm. This uncertainty should lead readers to be extremely cautious before using the presumptive maps published in the literature. Several tissues interact with osteo-progenitor cells: neural tube, surface ectoderm and dura mater. Analysis of genes in which mutations lead to abnormalities of the skull vault has partly revealed the molecular interactions. These are very complex and are the field of very numerous experimental investigations. In the relatively near future, we can hope to discover some of the molecular networks leading to the formation of these bony structures.

Morphological and molecular divergence of subspecies of Indian Bush Rats, <i>Golunda ellioti</i> Gray, 1837 (Rodentia: Muridae) from Sri Lanka

Genus Golunda is comprised of a single species of small bush rat endemic to southern Asia. In Sri Lanka, two subspecies are recognized, Golunda ellioti ellioti (Indian bush rat) and G. e. nuwara (Ceylon bush rat). These two subspecies can be differentiated by their tail length (longer in G. e. ellioti vs shorter in G. e. nuwara) fur type (short, harsh, spinous in G. e. ellioti vs long, soft and moderately fine in G. e. nuwara), colour of ventral pelage (light grey in G. e. ellioti vs bluish grey in G. e. nuwara) and microscopic hair anatomy (broader and shorter Guard Hair 1 with triangular and square shaped cross sections at the tip of the shield in G. e. ellioti vs narrower and longer Guard Hair 1 with circular to oval shaped cross sections in G. e. nuwara). In the present study, the divergence between the two subspecies was further evaluated using morphology (external and cranial) and molecular data (cytochrome-b, 16S and Rag 1 genes). We found that the brain case was comparatively rounded in G. e. ellioti and the interparietal bone was elongated in G. e. nuwara. Genetic distance between the two subspecies remain at subspecies level; 1.2% for cytochrome-b.

Juvenile Pleistocene tapir skull from Russells Reserve Cave, Bath County, Virginia: Implications for cold climate adaptations

A crushed, partial skull of a juvenile tapir was found with isolated post cranial elements and other fauna in Russells Reserve Cave (RRC), Bath County, Virginia. The cranium is undated but more than likely of late Pleistocene age. It possesses a complete deciduous premolar series and first permanent molars. The M2s have not yet erupted but are visible in the crypt. The RRC specimen is slightly older, ontogenetically, than the type specimen of Tapirus excelsus Simpson (= T. vereoensis) which is probably one of the youngest specimens known. Based upon cranial characters, primarily the lack of a dorsal flange on the maxilla, presence of an interparietal bone, anteriorly ascending cheek tooth row, and lack of sagittal crest, the RRC specimen is referred to the extinct species, Tapirus vereoensis. The sizes of the teeth and morphology of P1 and P2 of the RRC specimen are also consistent with an assignment to T. veroensis. Tapirus pinchaque, the modern woolly tapir, is adapted to cold Andean environments; cladistics and paleoecological studies suggest that cold adaptation may have evolved a second time in T. veroensis.

Incidence of interparietal bone in population of Northern Rajasthan

Incidence of interparietal bone in population of Northern Rajasthan

Locomotor activity, growth hormones, and systemic robusticity: An investigation of cranial vault thickness in mouse lines bred for high endurance running.

To use a mouse model to investigate the relationships among the components of the systemic robusticity hypothesis (SRH): voluntary exercise on wheels, spontaneous physical activity (SPA) in cages, growth hormones, and skeletal robusticity, especially cranial vault thickness (CVT). Fifty female mice from lines artificially selected for high running (HR) and 50 from nonselected control (C) lines were housed in cages with (Active) or without wheels (Sedentary). Wheel running and SPA were monitored daily. The experiment began at 24-27 days of age and lasted 12 weeks. Food consumption was measured weekly. Mice were skeletonized and their interparietal, parietal, humerus, and femur were µCT scanned. Mean total thickness of the parietal and interparietal bones was determined, along with thickness of the cortical and diploe layers individually. Geometric cross-sectional indicators of strength were calculated for the long bones. Blood samples were assayed for IGF-1 and IGFBP-3. Physical activity differed significantly among groups, based both on linetype (C vs. HR) and activity (A vs. S). However, contrary to our predictions, the ratio of IGF-1 to IGFBP-3 was higher in C mice than in HR mice. Neither CVT nor postcranial robusticity was affected by linetype or activity, nor were most measures of CVT and postcranial robusticity significantly associated with one another. Our results fail to provide support for the systemic robusticity hypothesis, suggesting it is important to rethink the long-standing theory that increased CVT in Homo erectus reflects increased physical activity compared other hominin species.

Bone marker gene expression in calvarial bones: different bone microenvironments

BackgroundIn calvarial mice, mesenchymal stem cells (MSCs) differentiate into osteoprogenitor cells and then differentiate into osteoblasts that differentiate into osteocytes, which become embedded within the bone matrix. In this case, the cells participating in bone formation include MSCs, osteoprogenitor cells, osteoblasts and osteocytes. The calvariae of C57BL/KaLwRijHsD mice consist of the following five bones: two frontal bones, two parietal bones and one interparietal bone. This study aimed to analyse some bone marker genes and bone related genes to determine whether these calvarial bones have different bone microenvironments.MethodsC57BL/KaLwRijHsD calvariae were carefully excised from five male mice that were 4–6 weeks of age. Frontal, parietal, and interparietal bones were dissected to determine the bone microenvironment in calvariae. Haematoxylin and eosin staining was used to determine the morphology of different calvarial bones under microscopy. TaqMan was used to analyse the relative expression of Runx2, OC, OSX, RANK, RANKL, OPG, N-cadherin, E-cadherin, FGF2 and FGFR1 genes in different parts of the calvariae.ResultsHistological analysis demonstrated different bone marrow (BM) areas between the different parts of the calvariae. The data show that parietal bones have the smallest BM area compared to frontal and interparietal bones. TaqMan data show a significant increase in the expression level of Runx2, OC, OSX, RANKL, OPG, FGF2 and FGFR1 genes in the parietal bones compared with the frontal and interparietal bones of calvariae.ConclusionThis study provides evidence that different calvarial bones, frontal, parietal and interparietal, contain different bone microenvironments.

Connexin43 and Runx2 Interact to Affect Cortical Bone Geometry, Skeletal Development, and Osteoblast and Osteoclast Function.

The coupling of osteoblasts and osteocytes by connexin43 (Cx43) gap junctions permits the sharing of second messengers that coordinate bone cell function and cortical bone acquisition. However, details of how Cx43 converts shared second messengers into signals that converge onto essential osteogenic processes are incomplete. Here, we use in vitro and in vivo methods to show that Cx43 and Runx2 functionally interact to regulate osteoblast gene expression and proliferation, ultimately affecting cortical bone properties. Using compound hemizygous mice for the Gja1 (Cx43) and Runx2 genes, we observed a skeletal phenotype not visible in wild-type or singly hemizygous animals. Cortical bone analysis by micro-computed tomography (μCT) revealed that 8-week-old male, compound Gja1+/- Runx2+/- mice have a marked increase in cross-sectional area, endosteal and periosteal bone perimeter, and an increase in porosity compared to controls. These compound Gja1+/- Runx2+/- mice closely approximate the cortical bone phenotypes seen in osteoblast-specific Gja1-conditional knockout models. Furthermore, μCT analysis of skulls revealed an altered interparietal bone geometry in compound hemizygotes. Consistent with this finding, Alizarin red/Alcian blue staining of 2-day-old Gja1+/- Runx2+/- neonates showed a hypomorphic interparietal bone, an exacerbation of the open fontanelles, and a further reduction in the hypoplastic clavicles compared to Runx2+/- neonates. Expression of osteoblast genes, including osteocalcin, osterix, periostin, and Hsp47, was markedly reduced in tibial RNA extracts from compound hemizygous mice, and osteoblasts from compound hemizygous mice exhibited increased proliferative capacity. Further, the reduced osteocalcin expression and hyperproliferative nature of osteoblasts from Cx43 deficient mice was rescued by Runx2 expression. In summary, these findings provide evidence that Cx43 and Runx2 functionally intersect in vivo to regulate cortical bone properties and affect osteoblast differentiation and proliferation, and likely contributes to aspects of the skeletal phenotype of Cx43 conditional knockout mice. © 2017 American Society for Bone and Mineral Research.