Swim-Training Changes the Spatio-Temporal Dynamics of Skeletogenesis in Zebrafish Larvae (Danio rerio)

Abstract

Fish larvae experience many environmental challenges during development such as variation in water velocity, food availability and predation. The rapid development of structures involved in feeding, respiration and swimming increases the chance of survival. It has been hypothesized that mechanical loading induced by muscle forces plays a role in prioritizing the development of these structures. Mechanical loading by muscle forces has been shown to affect larval and embryonic bone development in vertebrates, but these investigations were limited to the appendicular skeleton. To explore the role of mechanical load during chondrogenesis and osteogenesis of the cranial, axial and appendicular skeleton, we subjected zebrafish larvae to swim-training, which increases physical exercise levels and presumably also mechanical loads, from 5 until 14 days post fertilization. Here we show that an increased swimming activity accelerated growth, chondrogenesis and osteogenesis during larval development in zebrafish. Interestingly, swim-training accelerated both perichondral and intramembranous ossification. Furthermore, swim-training prioritized the formation of cartilage and bone structures in the head and tail region as well as the formation of elements in the anal and dorsal fins. This suggests that an increased swimming activity prioritized the development of structures which play an important role in swimming and thereby increasing the chance of survival in an environment where water velocity increases. Our study is the first to show that already during early zebrafish larval development, skeletal tissue in the cranial, axial and appendicular skeleton is competent to respond to swim-training due to increased water velocities. It demonstrates that changes in water flow conditions can result into significant spatio-temporal changes in skeletogenesis.

Dynamic skeletogenesis in fishes: Insight of exercise training on developmental plasticity

“…In both cases, the most responsive elements are the latter formed peripheral elements in the dorsal and anal fins, and the neural and haemal elements of preural centra in the caudal fin. Similar lines of evidence were recently reported Young and Badyaev, 2010;Fiaz et al, 2012) indicating that the latter formed elements in developing endoskeleton have a greater susceptibility to display plastic response with regards to changes in environmental conditions (or epigenetic factors). By analyzing the mechanical load exerted through muscle stimulation on the developing bony foraging apparatus of shrews (Sorex monticolus), Young and Badyaev (2010) found that the size and shape of the mandible is strongly influenced in late, but not in early, ossifying regions of the bone.…”

“…Zebrafish (Danio rerio) larvae subjected to swimming exercise showed an acceleration of ossification for the caudal fin elements; the ossification of hypurals and lepidotrichia occurs 15 days post-fertilization earlier in trained fish than in control fishes (Unpublished thesis). In two recent studies, it has been shown that exercise training changes the timing of formation of cartilages and bones in fishes Fiaz et al, 2012). By using different specimens and treatments, Cloutier et al (2010) have shown changes in the timing of ossification in specimens of S. alpinus reared at lower water velocities (i.e., slow velocity ¼ 0.38 cm s -1 and fast velocity ¼ 0.51 cm s -1 ) than tested in the present study.…”

“…Indeed, we found out that the effect of an increase of water velocity mainly induces changes in the developmental progress in all fins; the responsive elements ossify at comparatively smaller size at faster velocity. It is suggested that rearing fish in differential water velocity may affect their locomotion and thus may change the mechanical stress exerted on developing endoskeletal elements (Fischer-Rousseau et al, 2009;Cloutier et al, 2010;Fiaz et al, 2010Fiaz et al, , 2012. In this context, several lines of evidences have shown the correlative link between environmental changes such as differential water velocity and plasticity in timing of skeletogenesis (rather than changes in the relative order of developmental events) in fishes.…”

“…A wide range of plastic responses has been reported in the literature. Focusing on anatomical plasticity, the following traits exemplify the types of responses: size [e.g., gills (Crispo and Chapman, 2010), brain (Crispo and Chapman, 2010), head (Meyer, 1987), body (Pakkasmaa and Piironen, 2001;Peres-Neto and Magnan, 2004;Georgakopoulou et al, 2007;Grü nbaum et al, 2008;Schmidt and Starck, 2010;Frommen et al, 2011;Kawajiri et al, 2011), fins (Fischer-Rousseau et al, 2009)] and shape changes [e.g., head (Meyer, 1987), pharyngeal (Muschnick et al, 2011) and oral jaws (Meyer, 1987), body (Pakkasmaa and Piironen, 2001;Peres-Neto and Magnan, 2004;Georgakopoulou et al, 2007;Grü nbaum et al, 2007;Fischer-Rousseau et al, 2009;Garduno-Paz et al, 2010;Frommen et al, 2011)], bone matrix (Totland et al, 2011), number of serially repeated elements [e.g., pharyngeal teeth, vertebrae, fin rays, spines (Arratia and Schultze, 1992;Mabee et al, 2000;Georgakopoulou et al, 2007;Shkil et al, 2010;Kawajiri et al, 2011)], and timing of ossification Moksness, 1994, 1997;Fuiman et al, 1998;Mabee et al, 2000;Cloutier et al, 2010, Fiaz et al, 2012. It is also known that fin positioning is plastic with respect to changes in hydrodynamic conditions …”

The enigmas of bone without osteocytes

“…Modeling therefore results in a net increase or loss of bone material, and is thus important in bone development, bone growth and bone adaptation to changing loads. 4,6,40 Many studies have concluded that fish bone responds to increased loading by the process of modeling; however, most of these were conducted using fish with cellular bones (for example, Deschamps et al, 41 Eissa et al, 42 Fiaz et al 43 and Totland et al 44 ). The few studies that have focused on acellularboned fishes have provided somewhat secondary evidence for modeling.…”