Retinoic acid controls proper head-to-trunk linkage in zebrafish by regulating an anteroposterior somitogenetic rate difference.

During vertebrate development, the primary body axis elongates towards the posterior and is periodically divided into somites, which give rise to the vertebrae, skeletal muscles and dermis. Somites form periodically from anterior to posterior, and the anterior somites form in a more rapid cycle than the posterior somites. However, how this anteroposterior (AP) difference in somitogenesis is generated and how it contributes to the vertebrate body plan remain unclear. Here, we show that the AP difference in zebrafish somitogenesis originates from a variable overlapping segmentation period between one somite and the next. The AP difference is attributable to spatiotemporal inhibition of the clock gene her1 via retinoic acid (RA) regulation of the transcriptional repressor ripply1. RA depletion thus disrupts timely somite formation at the transition, eventually leading to the loss of one somite and the resultant cervical vertebra. Overall, our results indicate that RA regulation of the AP difference is crucial for proper linkage between the head and trunk in the vertebrate body plan.

Antiangiogenic Activity of n-hexane Insoluble Fraction and Its Tylophorine Component from Ficus septica Leaves in Chicken Chorioallantoic Membrane Induced by bFGF.

OBJECTIVE: Ficus septica is an Indonesian medicinal plant traditionally used to treat various illness, including cancer. The n-hexane insoluble fraction of the ethanolic extract of F. septica leaves (HIFFS) shows a potential anticancer activity against breast cancer cell line T47D. Considering that angiogenesis is a pivotal factor in malignant cancer growth, progression, and invasion, we aimed to investigate the antiangiogenic effect of HIFFS on chicken chorioallantoic membrane (CAM) induced by bFGF. We also evaluated tylophorine, the cytotoxic alkaloid of F. septica. METHODS: Chicken CAM was used to assess the antiangiogenic effect. Fertilized chicken eggs were induced with basic fibroblast growth factor (bFGF) ex ovo. Prior to bFGF induction, HIFFS (2.33, 4.65, 6.98, and 9.30 µg/mL) or tylophorine (9.20 µM) was added (10 µL) to a paper disk and implanted to the CAM. After 48 h of incubation, each treatment group was photographed, and the number of new blood vessel was calculated and compared with that in the solvent-treated group to determine the antiangiogenic activity. Histology of the CAM was evaluated after hematoxylin-eosin and Mallory acid fuchsin staining. RESULTS: We found that HIFFS at low concentrations (2.33, 4.65, 6.98, and 9.30 µg/mL) inhibited angiogenesis activity (31.87, 41.99, 53.65, and 70.08, respectively) in chicken CAM induced by bFGF. Tylophorine (9.20 µM) also showed similar antiangiogenesis activity in the same model. Histopathology analysis revealed that HIFFS and tylophorine reduced the number of new blood vessels in CAM induced by bFGF. CONCLUSION: HIFFS and tylophorine showed antiangiogenic effect on chicken CAM induced by bFGF. This finding emphasized the potential of F. septica as a candidate anticancer agent.

The water-hopping kinematics of the tree-climbing fish, Periophthalmus variabilis.

In this communication, we describe the water-hopping kinematics of the dusky-gilled mudskipper (Periophthalmus variabilis), and by doing so elucidate an entirely new form of fish locomotion that has yet to be reported in the public domain. Water-hopping is defined herein as an ability to hop once, or in succession, on the surface of water without full submergence and without a fin-guided glide. We find that taxiing on the water surface is the predominating kinematic movement used for the execution of successful water-hops. We observe that an initial concentric ripple forms as the mudskipper impacts the water, and that subsequent taxiing on the water surface generates a sinusoid-like ripple pattern in the water prior to take off. Interestingly whilst airborne, the pectoral fins of P. variabilis appear to remain stationary, only to be deployed upon contact with the water. When landing back onto the surface of the water, P. variabilis makes the initial contact via its pelvic region, occasionally extending its pectoral fins during its descent. The reasons for pectoral and pelvic fin extension are unclear, however, there may be either aerodynamic or hydrodynamic benefits in its doing so. This motion furthermore prepares the mudskipper for either, a follow-on water-hop, or a discontinuation of movement altogether, as the body of the mudskipper becomes aligned in a way conducive to either. P. variabilis will launch and land using both, horizontal surfaces such as littorals, and inclined-to-vertical surfaces such as rocks and trees.

The Impact Behaviour of Crab Carapaces in Relation to Morphology.

Brachyuran crab carapaces are protective, impact-resistant exoskeletons with elaborate material microstructures. Though several research efforts have been made to characterise the physical, material and mechanical properties of the crab carapace, there are no studies detailing how crab morphologies might influence impact resistance. The purpose of this paper is to characterise and compare Brachyuran crab carapace morphologies in relation to their impact properties, using opto-digital, experimental and numerical methods. We find that crab carapaces with both extended carapace arc-lengths and deep carapace grooves lose stiffness rapidly under cyclic impact loading, and fail in a brittle manner. Contrarily, carapaces with smaller arc lengths and shallower, more broadly distributed carapace grooves are more effective in dissipating stresses caused by impact throughout the carapace structure. This allows them to retain stiffness for longer, and influences their failure mode, which is ductile (denting), rather than brittle fracture. The findings in this paper provide new bioinspired approaches for the geometrical designs by which means material failure under cyclic impact can be controlled and manipulated.

The significance of pelvic fin flexibility for tree climbing fish.

In this article, we compare the characteristics of biomechanical attachment exhibited by two morphologically different mudskipper species, Boleophthalmus boddarti (with fused pelvic fins) and Periophthalmus variabilis (with unfused pelvic fins). P. variabilis is a tree and rock climber while B. boddarti dwells in the muddy shallows and is unable to climb. Our aim in this article is to determine whether it is predominantly chemical or morphological properties of the pelvic fins from each species that may allow P. variabilis to climb trees whilst preventing B. boddarti from doing the same. To fulfil our objective we perform friction and suction resistance tests, Fourier transform infrared spectroscopy of the mucosal secretions under the fins, direct geometrical measurements and finite element modelling. We find that B. boddarti has considerable resistance to pull-off forces, while P. variabilis has greater frictional resistance. Both species produce mucopolysaccaharides that we suggest aid Stefan adhesion to different substrates. P. variabilis fins are, nevertheless, considerably more flexible than those of B. boddarti and we conclude that P. variabilis is consequently able to maintain a more intimate surface area of contact with underlying material, which aids Stefan adhesion, increases frictional resistance, and helps it to climb trees.

Morphological and mechanical characterisation of the hindwing nodus from the Libellulidae family of dragonfly (Indonesia).

In this communication, the morphologies and mechanical characteristics of nodi from the hindwings of seven Indonesian Libellulidae dragonfly species are identified. Geometrical analyses reveal that in all species, the shape of dorsal face resilin is relatively long and thin while ventral face resilin covers a greater surface area than dorsal face resilin, and is shaped like a hook. Finite element analyses reveal that the magnitude of strain energy may differ considerably between species, even though the locations of highest strain energy are usually the same. Importantly, a correlation is found to exist between the mechanical forces that build up in the resilin, the face under investigation (dorsal or ventral) and the elongational shape factor of the resilin.