Split-weaning before altrenogest synchronization of multiparous sows alters follicular development and reduces embryo survival.

This study used split-weaning (SW) to induce differences in follicle size at weaning and study its consequences for follicle development during and after post-weaning altrenogest feeding and for reproductive performance. Multiparous sows (n=47) were assigned to SW (n=23; litter size reduced to the six smallest piglets 3 days before weaning) or control (C; n=24; normal weaning). Altrenogest (20 mg/day) was fed to all 47 sows from Day -1 till Day 5 (complete weaning = Day 0). Follicle size on Day 1, 2 and 8 was smaller in C than in SW (p ≤ 0.05). Ovulation rate was similar, but C sows had higher embryo survival rate (ESR) than SW sows (83 ± 19 and 58 ± 31%, respectively; p=0.001). SW sows with low ESR (<63%; n=10) had a greater follicle size on days 3-6 than SW sows with high ESR (>63%; n=10; p ≤ 0.04). A decrease in follicle size between Day 5 and 6 of altrenogest feeding was associated with increased ESR in both treatments (p=0.002). Follicle pool analyses (assessment of all follicles >2 mm) revealed that on Day 3, sows with low ESR had a higher % of follicles >5 mm compared with sows with high ESR (30% vs 10%; p=0.04). Thus, sows in which follicle growth was less suppressed during altrenogest feeding had a lower ESR. These effects on follicle development and ESR were more pronounced in split-weaned sows.

Endurance exercise differentially stimulates heart and axial muscle development in zebrafish (Danio rerio).

Mechanical load is an important factor in the differentiation of cells and tissues. To investigate the effects of increased mechanical load on development of muscle and bone, zebrafish were subjected to endurance swim training for 6 h/day for 10 wk starting at 14 days after fertilization. During the first 3 wk of training, trained fish showed transiently increased growth compared with untrained (control) fish. Increased expression of proliferating cell nuclear antigen suggests that this growth is realized in part through increased cell proliferation. Red and white axial muscle fiber diameter was not affected. Total cross-sectional area of red fibers, however, was increased. An improvement in aerobic muscle performance was supported by an increase in myoglobin expression. At the end of 10 wk of training, heart and axial muscle showed increased expression of the muscle growth factor myogenin and proliferating cell nuclear antigen, but there were major differences between cardiac and axial muscle. In axial muscle, expression of the "slow" types of myosin and troponin C was increased, together with expression of erythropoietin and myoglobin, which enhance oxygen transport, indicating a shift toward a slow aerobic phenotype. In contrast, the heart muscle shifts to a faster phenotype but does not become more aerobic. This suggests that endurance training differentially affects heart and axial muscle.

Effects of decreased muscle activity on developing axial musculature in nicb107 mutant zebrafish (Danio rerio).

The present paper discusses the effects of decreased muscle activity (DMA) on embryonic development in the zebrafish. Wild-type zebrafish embryos become mobile around 18 h post-fertilisation, long before the axial musculature is fully differentiated. As a model for DMA, the nic(b107) mutant was used. In nic(b107) mutant embryos, muscle fibres are mechanically intact and able to contract, but neuronal signalling is defective and the fibres are not activated, rendering the embryos immobile. Despite the immobility, distinguished slow and fast muscle fibres developed at the correct location in the axial muscles, helical muscle fibre arrangements were detected and sarcomere architecture was generated. However, in nic(b107) mutant embryos the notochord is flatter and the cross-sectional body shape more rounded, also affecting muscle fibre orientation. The stacking of sarcomeres and myofibril arrangement show a less regular pattern. Finally, expression levels of several genes were changed. Together, these changes in expression indicate that muscle growth is not impeded and energy metabolism is not changed by the decrease in muscle activity but that the composition of muscle is altered. In addition, skin stiffness is affected. In conclusion, the lack of muscle fibre activity did not prevent the basal muscle components developing but influenced further organisation and differentiation of these components.

Identification and characterisation of two runx2 homologues in zebrafish with different expression patterns.

Genome and gene duplications are considered to be the impetus to generate new genes, as the presence of multiple copies of a gene allows for paralogues to adopt novel function. After at least two rounds of genome/gene duplication, the Runt gene family consists of three members in vertebrates, instead of one in invertebrates. One of the family members, Runx2, plays a key role in the development of bone, a tissue that first occurs in vertebrates. The family has thus gained new gene function in the course of evolution. Two Runx2 genes were cloned in the vertebrate model system the zebrafish (Danio rerio). The expression patterns of the two genes differ and their kinetics differ up to four fold. In addition, splice forms exist that are novel when compared with mammals. Together, these findings comprise opportunities for selection and retention of the paralogues towards divergent and possibly new function.

Oxygen balance for small organisms: an analytical model.

An analytical model is developed that describes oxygen transport and oxygen consumption for small biological structures without a circulatory system. Oxygen inside the organism is transported by diffusion alone. Oxygen transfer towards the organism is retarded by a thin static fluid film at the surface of the organism. The thickness of this film models the outward water conditions, which may range from completely stagnant water conditions to so-called well-stirred water conditions. Oxygen consumption is concentration-independent above a specified threshold concentration (regulator behaviour) and is proportional to the oxygen concentration below this threshold (conformer behaviour). The model takes into account shape and size of the organism and predicts the transition from (pure) regulator behaviour to (pure) conformer behaviour, as well as the mean oxygen consumption rate. Thereby the model facilitates a proper analysis of the physical constraints set on shape and size of organisms without an active internal oxygen transport mechanism. This analysis is carried out in some detail for six characteristic shapes (infinite sheet, cylinder and beam; finite cylinder, sphere and block). In a well-stirred external medium, a flattened shape appears to be the most favourable for oxygen supply, while a compact shape (cube) is more favourable if the external medium is nearly stagnant. The theoretical framework is applied to oxygen consumption data of eight teleost embryos. This reveals relative insensitivity to external flow conditions in some species (e.g., winter flounder, herring), while others appear to rely on external stirring for a proper oxygen supply (e.g., largemouth bass). Interestingly, largemouth bass is the only species in our analysis that exhibits 'fin-fanning'.

Consequences of forced convection for the constraints on size and shape in embryos.

Previously, predictions of the maximum size of biological objects based on oxygen availability have been made for both zero and infinite water velocity around the object. In reality, however, water velocity is always intermediate between zero and infinity. We predicted maximum size and optimal shape of biological objects, pending the velocity of water around them. We assumed oxygen inside the object to be transported by diffusion and outside the object by diffusion and convection. Fick's first law of diffusion describes the inner transport. For the outer transport, we relied on semi-empirical relations between mass transport and flow conditions (Friedlander's equations). To keep mathematical complexity acceptable, we restricted ourselves to the analysis of a sphere and a cylinder in cross flow. If water velocity is low, a spherical shape is most favourable for gas exchange. If water velocity is high, an elongated and flattened shape is more favourable. A size-dependent intermediate velocity exists where shape does not matter (10(-4) m s(-1)for teleost embryos). Teleost embryos are typically exposed to flow velocities equal to or larger than 10(-4) m s(-1), making an elongated shape more favourable than a spherical one. Although teleost eggs are typically spherical, the oxygen-consuming embryos inside are indeed elongated.

Physical constraints on body size in teleost embryos.

All members of the subphylum "Vertebrata" display the characteristics of the vertebrate body plan. These characteristics become apparent during the phylotypic period, in which all vertebrate embryos have a similar body shape and internal organization. Phylogenetic constraints probably limit the morphological variation during the phylotypic period. Physical laws, however, also limit growth and morphogenesis in embryos. We investigated to what extent oxygen availability-as a physical constraint-might limit morphological variation during embryonic development. This paper gives an analysis of time-dependent diffusion into spherical embryos without a circulatory system. Equilibrium appeared to settle in about 1.5 min in running water and in about 10min in stagnant water. Hence, steady-state conditions were assumed and expressions for maximum body size were obtained for spherical, cylindrical and sheet-like embryos in running water and spherical embyros in stagnant water. Predictions of the model based on literature data suggest that in running water-both for spherical, cylindrical and sheet-like embryos-diffusion alone suffices to cover the oxygen needs of a teleost embryo in its phylotypic period. The size of carp (Cyprinus carpio) and African catfish (Clarias gariepinus) embryos is very close to the predicted maximum. This suggests that in these species the development of a functional circulatory system is correlated with the onset of oxygen shortage. Oxygen availability is therefore a potentially important physical constraint on embryonic morphology, though in most species the circulatory system becomes functional well in advance of the onset of oxygen shortage and other demands than oxygen delivery (e.g. nutrient distribution, waste disposal, osmoregulation) might require the development of a circulatory system.