Biology subjects

Nowlan, N. C.

Publications and source records attributed to Nowlan, N. C..

6 recordsLinked to original sources

bioRxiv2024

Dynamics of postnatal bone development and epiphyseal synostosis in the caprine autopod

Bones develop to structurally balance strength and mobility. Bone developmental dynamics are influenced by whether an animal is ambulatory at birth (i.e., precocial). Precocial species, such as goats, develop advanced skeletal maturity in utero, making them useful models for studying the dynamics of bone formation under mechanical load. Here, we used microcomputed tomography and histology to characterize postnatal bone development in the autopod of the caprine lower forelimb. The caprine autopod features two toes, fused by metacarpal synostosis (i.e., bone fusion) prior to birth. Our analysis focused on the phalanges 1 (P1) and metacarpals of the goat autopod from birth through adulthood (3.5 years). P1 cortical bone densified rapidly after birth (half-life using one-phase exponential decay model ({tau}1/2 = 1.6 {+/-} 0.4 months), but the P1 cortical thickness increased continually through adulthood ({tau}1/2 = 7.2 {+/-} 2.7 mo). Upon normalization by body mass, the normalized polar moment of inertia of P1 cortical bone was constant over time, suggestive of structural load adaptation. P1 trabecular bone increased in trabecular number ({tau}1/2 = 6.7 {+/-} 2.8 mo) and thickness ({tau}1/2 = 6.6 {+/-} 2.0 mo) until skeletal maturity, while metacarpal trabeculae grew primarily through trabecular thickening ({tau}1/2 = 7.9 {+/-} 2.2 mo). Unlike prenatal fusion of the metacarpal diaphysis, synostosis of the epiphyses occurred postnatally, prior to growth plate closure, through a unique fibrocartilaginous endochondral ossification. These findings implicate ambulatory loading in postnatal bone development of precocial goats and identify a novel postnatal synostosis event in the caprine metacarpal epiphysis.

developmental biology↗

bioRxiv2023

Cyclical compression loading is the dominant mechanoregulator of synovial joint morphogenesis

Mechanical stimuli arising from fetal movements are critical factors underlying joint growth. Abnormal fetal movements negatively affect joint shape features with important implications for joint function and health, but the mechanisms by which mechanical forces due to fetal movements influence joint growth are still unclear. In this research, we integrated cell-level data into a novel mechanobiological model of zebrafish jaw joint morphogenesis to identify links between the mechanical stimuli arising from movement and patterns of growth. Larval zebrafish jaw joint growth patterns were quantified from tracked cell-data at several successive developmental stages in the presence or absence of movements. Pharmacological immobilisation, prior to the onset of jaw movements, resulted in growth rate decreases which were stronger along the ventrodorsal axis. Simulations of joint morphogenesis, based on the quantified cell-level data and which integrated mechanical stimuli arising from simulated jaw movements, were used to test hypotheses relating specific mechanical stimuli with the local changes in size and shape. Different types of mechanical stimulation were incorporated into the simulation to provide the mechanoregulated component on growth in addition to the baseline (non mechanoregulated) growth which occurs in the immobilised animals. We found that the magnitude of compression experienced during joint motion when included as the stimulus for mechanoregulated growth could not predict the real, normally loaded shaped joints. However, when the dynamic changes caused by the application of cyclical compression was implemented as the stimulus for mechanoregulated growth, the sizes and shapes of joints were correctly simulated. We conclude therefore that the cyclical application of compression loading due to the dynamic nature of fetal movements underlies the mechanoregulation of prenatal joint morphogenesis. Our results provide a fundamental advance in our understanding of mechanoregulation of the developing joint and increase our understanding of the origins of conditions such as hip dysplasia and arthrogryposis. Author summaryThe mechanical forces caused by fetal movements are important for normal development of the skeleton, and in particular for joint shape. Several common developmental musculoskeletal conditions such as developmental dysplasia of the hip and arthrogryposis are associated with reduced or restricted fetal movements. Paediatric joint malformations impair joint function and can be debilitating. To understand the origins of such conditions, it is essential to understand how the mechanical forces arising from movements influence joint growth and shape. In this research, we used a computational model of joint growth applied to the zebrafish jaw joint to study the impact of fetal movements on joint growth and shape. We find that the cyclical application of compression loading is critical to the normal growth and shape of the developing joint. Our findings implicate that dynamic compression must be targeted when developing strategies for the treatment of musculoskeletal conditions through targeted physiotherapy.

developmental biology↗

bioRxiv2022

Mechanoregulatory role of TRPV4 in prenatal skeletal development

Biophysical cues are essential for guiding skeletal development, but the mechanisms underlying the physical regulation of cartilage and bone formation are unknown. TRPV4 is a cell membrane ion channel responsible for transducing mechanical stimuli as a means of regulating skeletal cell homeostatic processes. Dysregulation of TRPV4 is associated with several skeletal developmental pathologies, indicating its involvement in cartilage and bone development, potentially in a mechanosensing capacity. In this study, we test the hypothesis that mechanically mediated prenatal skeletogenesis depends on TRPV4 activity. We first validate a novel model where we establish that dynamically loading embryonic mouse hindlimb explants cultured ex vivo promotes joint cartilage growth and morphogenesis, but not diaphyseal mineralization. We next reveal that TRPV4 protein expression is mechanically regulated and spatially localized to patterns of high biophysical stimuli in the femoral condyles of cultured limbs. Finally, we demonstrate that TRPV4 activity is crucial for the mechanical regulation of joint cartilage growth and shape, mediated via the control of cell proliferation and matrix biosynthesis, indicating a mechanism by which mechanical loading could direct morphogenesis during joint formation. We conclude that the regulatory pathways initiated by TRPV4 mechanotransduction are essential for the for the cartilage response to physical stimuli during skeletal development. Therefore, TRPV4 may be a valuable target for the development of therapeutic skeletal disease modifying drugs and developmentally-inspired tissue engineering strategies for skeletal repair.

developmental biology↗

bioRxiv2022

Growth orientations, rather than heterogeneous growth rates, dominate jaw joint morphogenesis in the larval zebrafish

In early limb embryogenesis, synovial joints acquire specific shapes which determine joint motion and function. The process by which the opposing cartilaginous joint surfaces are moulded into reciprocal and interlocking shapes, called joint morphogenesis, is one of the least understood aspect of joint formation and the cell-level dynamics underlying it are yet to be unravelled. In this research, we quantified key cellular dynamics involved in growth and morphogenesis of the zebrafish jaw joint and synthesised them in a predictive computational simulation of joint development. Cells in larval zebrafish jaw joints labelled with cartilage markers were tracked over a forty-eight hour time window using confocal imaging. Changes in distance and angle between adjacent cell centroids resulting from cell rearrangement, volume expansion and extracellular matrix (ECM) deposition were measured and used to calculate the rate and direction of local tissue deformations. We observed spatially and temporally heterogeneous growth patterns with marked anisotropy over the developmental period assessed. There was notably elevated growth at the level of the retroarticular process of the Meckels cartilage, a feature known to undergo pronounced shape changes during zebrafish development. Analysis of cell dynamics indicated a dominant role for cell volume expansion in growth, with minor influences from ECM volume increases and cell intercalation. Cell proliferation in the joint was minimal over the timeframe of interest. Synthesising the dynamic cell data into a finite element model of jaw joint development resulted in accurate shape predictions. Our biofidelic computational simulation demonstrated that zebrafish jaw joint growth can be reasonably approximated based on cell positional information over time, where cell positional information derives mainly from cell orientation and cell volume expansion. By modifying the input parameters of the simulation, we were able to assess the relative contributions of heterogeneous growth rates and of growth orientation. The use of uniform rather than heterogeneous growth rates only minorly impacted the shape predictions whereas isotropic growth fields resulted in altered shape predictions. The simulation results suggest that growth anisotropy is the dominant influence on joint growth and morphogenesis. This study addresses the gap of the cellular processes underlying joint morphogenesis, with implications for understanding the aetiology of developmental joint disorders such as developmental dysplasia of the hip and arthrogryposis.

developmental biology↗

bioRxiv2019

Effects of abnormal muscle forces on prenatal joint morphogenesis in mice

Fetal movements are essential for normal development of the human skeleton. When fetal movements are reduced or restricted, infants are at higher risk of developmental dysplasia of the hip and arthrogryposis (multiple joint contractures). Joint shape abnormalities have been reported in mouse models with abnormal or absent musculature, but the effects on joint shape in such models have not been quantified or characterised in detail. In this study, embryonic mouse forelimbs and hindlimbs at a single developmental stage (Theiler Stage 23) with normal, reduced or absent muscle were imaged in 3D. Skeletal rudiments were virtually segmented and rigid image registration was used to reliably align rudiments with each other, enabling repeatable assessment and measurement of joint shape differences between normal, reduced-muscle and absent muscle groups. We demonstrate qualitatively and quantitatively that joint shapes are differentially affected by a lack of, or reduction in, skeletal muscle, with the elbow joint being the most affected of the major limb joints. Surprisingly, the effects of reduced muscle were often more pronounced than those of absent skeletal muscle, indicating a complex relationship between muscle mass and joint morphogenesis. These findings have relevance for human developmental disorders of the skeleton in which abnormal fetal movements are implicated, particularly developmental dysplasia of the hip and arthrogryposis.

developmental biology↗

bioRxiv2018

Prenatal growth map of the mouse knee joint by mean of deformable registration technique

Joint morphogenesis is the process during which distinct and functional joint shapes emerge during pre- and post-natal joint development. In this study, a repeatable semi-automatic protocol capable of providing a 3D realistic developmental map of the prenatal mouse knee joint was designed by combining Optical Projection Tomography imaging (OPT) and a deformable registration algorithm (Sheffield Image Registration toolkit, ShIRT). Eleven left limbs of healthy murine embryos were scanned with OPT (voxel size: 14.63[1/4]m) at two different stages of development: Theiler stage (TS) 23 (approximately 14.5 embryonic days) and 24 (approximately 15.5 embryonic days). One TS23 limb was used to evaluate the precision of the displacement predictions for this specific case. The remaining limbs were then used to estimate Developmental Tibia and Femur Maps. Acceptable uncertainties of the displacement predictions were found for both epiphyses (between 0.7 and 1.4 m, along all directions and anatomical sites) for nodal spacing of 1 voxel. The protocol was found to be reproducible with maximum Modified Housdorff Distance differences equal to 1.9 m and 1.5 m for the tibial and femoral epiphyses respectively. The effect of the initial shape of the rudiment affected the developmental maps by 21.7 m and 21.9 m for the tibial and femoral epiphyses respectively, which correspond to 1.4 and 1.5 times the voxel size. To conclude, this study proposes a repeatable semi-automatic protocol capable of providing mean 3D realistic developmental map of a developing rudiment allowing researchers to study how growth and adaptation are directed by biological and mechanobiological factors.

bioengineering↗