PHOSPHO1 is a phosphoethanolamine/phosphocholine phosphatase that has previously been implicated in generating inorganic phosphate (P(i)) for matrix mineralization. In this study, we have investigated PHOSPHO1 mRNA expression during embryonic development in the chick. Whole-mount in situ hybridization indicated that PHOSPHO1 expression occurred prior to E6.5 and was initially restricted to the bone collar within the mid-shaft of the diaphysis of long bones but by E11.5 expression was observed over the entire length of the diaphysis. Alcian blue/alizarin red staining revealed that PHOSPHO1 expression seen in the primary regions of ossification preceded the deposition of mineral, suggesting that it is involved in the initial events of mineral formation. We isolated MVs from growth plate chondrocytes and confirmed the presence of high levels of PHOSPHO1 by immunoblotting. Expression of PHOSPHO1, like TNAP activity, was found to be up-regulated in MVs isolated from chondrocytes induced to differentiate by the addition of ascorbic acid. This suggests that both enzymes may be regulated by similar mechanisms. These studies provide for the first time direct evidence that PHOSPHO1 is present in MVs, and its developmental expression pattern is consistent with a role in the early stages of matrix mineralization.

Growth plate chondrocytes progress through a proliferative phase before acquiring a terminally-differentiated phenotype. In this study we used Percoll density gradients to separate chick growth plate chondrocytes into populations of different maturational phenotype. By applying agarose gel differential display to these populations we cloned a cDNA encoding a novel 268 amino acid protein (3X11A). 3X11A contains two peptide motifs that are conserved in a recently identified superfamily of phosphotransferases. It is likely that 3X11A is a phosphatase, but its substrate specificity remains uncertain. 3X11A expression is upregulated 5-fold during chondrocyte terminal differentiation and its expression is approximately 100-fold higher in hypertrophic chondrocytes than in non-chondrogenic tissues. This suggests that 3X11A participates in a biochemical pathway that is particularly active in differentiating chondrocytes.

Glucocorticoids (GC) are used extensively in children and may cause growth retardation, which is in part due to the direct effects of GC on the growth plate. We characterised the ATDC5 chondrocyte cell line, which mimics the in vivo process of longitudinal bone growth, to examine the effects of dexamethasone (Dex) and prednisolone (Pred) during two key time points in the chondrocyte life cyclechondrogenesis and terminal differentiation. Additionally, we studied the potential for recovery following Dex exposure. During chondrogenesis, Dex and Pred exposure at 10 -8 M, 10 -7 M and 10 -6 M resulted in a significant mean reduction in cell number (28% vs 20%), cell proliferation (27% vs 24%) and proteoglycan synthesis (47% vs 43%) and increased alkaline phosphatase (ALP) activity (106% vs 62%), whereas the incidence of apoptosis was unaltered. Minimal effects were noted during terminal differentiation with both GC although all concentrations of Dex lowered apoptotic cell number. To assess catch-up growth the cells were incubated for a total of 14 days which included 1, 3, 7, 10 or 14 days exposure to 10 -6 M Dex, prior to the recovery period. Recovery of proteoglycan synthesis was irreversibly impaired following just one day exposure to Dex. Although cell number showed a similar pattern, significant impairment was only achieved following 14 days exposure. Irreversible changes in ALP activity were only noticed following 10 days exposure to Dex.In conclusion, GC have maximal effects during chondrogenesis; Dex is more potent than Pred and cells exposed to Dex recover but this may be restricted due to differential effects of GC on specific chondrocyte phenotypes.

No abstract

1. The effects of beak trimming on 16-week-old Brown Leghorn hens, housed individually in battery cages, was assessed by comparing their behaviour after trimming with their behaviour before trimming and with the behaviour of a sham-operated control group. 2. In the short-term, times spent feeding, drinking and preening decreased. 3. In the long-term, times spent preening and pecking at the cage decreased and times spent standing inactive increased, with no signs of returning to pretreatment values after 5 weeks. 4. During the first three weeks, times spent feeding and drinking decreased and during the first two weeks, times spent sitting dozing increased, but after 5 weeks these had returned to near pre-treatment values. 5. It is argued that pain is the most probable cause of these behavioural changes. 6. The decrease in welfare to the individual bird caused by this pain will conflict with any increase in welfare to the flock brought about by beak trimming; this should be considered before any decision to beak trim is taken.