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Zebrafish (Danio rerio) is a useful model for understanding biomedical properties of bone and are widely employed in developmental and genetics studies. Here, we have studied the development of zebrafish vertebral bone at the nanoscale from adolescence (6 months), early adulthood (10 months) to mid-life (14 months). Characterization of the bone was conducted using energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM) and PeakForce QNM atomic force microscopy (AFM) techniques. SEM and AFM revealed a lamellar structure with mineralized collagen fibrils. There was a significant increase in the wall thickness from 6 to 10 months (76%) and 10 months to 14 months (26%), which is positively correlated with nanomechanical behavior. An increase in the Ca/P ratio was found which was also positively correlated with nanomechanical properties. The change in mechanical properties and Ca/P are similar to those expected in humans when transitioning from adolescence to mid-life. We suggest that zebrafish serve as a suitable model for further studies on age-related changes in bone ultrastructure., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

The underlying pathogenic lesions of glycogen storage disease type II (GSD II) and the diversity of this disease among different species are still under exploration. Thus, we created an acid alpha-glucosidase (gaa) gene-mutated zebrafish model of GSD II and examined the sequential pathogenic changes. gaa mRNA and protein expression, enzymatic activity, and lysosomal glycogen accumulation were assessed, and the phenotypic changes were compared between wild-type (WT) and gaa-mutated zebrafish. The presence of a Δ13 frameshift mutation in the gaa gene was confirmed at both the DNA and transcribed mRNA levels by Sanger sequencing. The relative amount of gaa mRNA was decreased before 2 days postfertilization (dpf), after which it unexpectedly increased in the mutant compared with the WT zebrafish. Consistent with the mRNA expression, the Gaa enzymatic activity in the mutant was downregulated before 3 dpf, while the Gaa protein level was slightly decreased at 4 dpf and was maintained at a consistent level in the adult gaa mutant muscle tissue. However, more than half of the adult mutant zebrafish exhibited excessive glycogen accumulation in the liver and muscles, along with the presence of autophagosomes, as determined by transmission electron microscopy. Thus, we have successfully generated a frameshift mutation in the gaa gene in zebrafish. The unique gaa gene expression changes and mild GSD II features during the adult stage strongly indicate the existence of species-specific differences, as well as an underlying compensatory network, which may warrant further examination.