Quantitative evaluation of collagen type VI and SOD gene expression in the nuchal skin of human fetuses with trisomy 21.

OBJECTIVE: To investigate the involvement of the genes encoding for COL6A1, COLA2 and super-oxide dismutase (SOD) in the mechanism for the retention of subcutaneous fluid in fetuses with trisomy 21. METHODS: During a 7-month period (November 2004-May 2005), human fetal skin from the nuchal region was obtained from euploid fetuses and from fetuses with trisomy 21 following abortions and terminations of pregnancy. Cell cultures were performed from nuchal skin. Quantification of COL6A1, COL6A2, COL6A3 and SOD mRNAs were performed using real-time quantitative RT-PCR. RESULTS: Twelve fetuses were studied between 13-15 and 19-20 weeks of gestation including 7 cases of trisomy 21. A significant overexpression of genes of interest was demonstrated in trisomy 21 fetuses when compared with euploid fetuses, in the first and in the second trimester of pregnancy (p < 0.0001). CONCLUSION: This study demonstrates a homogeneous overexpression of the genes encoding for alpha1 and alpha2 chains of Collagen type VI, and SOD in nuchal skin of human trisomy 21 fetuses. Persistence of this overexpression in the second trimester of pregnancy, despite the absence of an enlarged nuchal translucency (NT), may characterize some compensatory mechanisms.

Fish growth rates modulate mercury concentrations in walleye (Sander vitreus) from eastern Canadian lakes.

The majority of the studies attempting to explain fluctuations of mercury (Hg) concentrations in fish from diverse aquatic ecosystems have invoked the influence of physico-chemical or environmental factors but has eluded that of strictly biological factors. In this study, we examine the relationship between Hg concentrations in walleye (Sander vitreus) muscles and their growth rates in 12 natural lakes located in four different regions of Quebec (Saint Lawrence Valley, Chibougamau, Abitibi, and Temiscamingue). Hg concentrations vs. total lengths of fish were described using polynomial regressions while growth rates (lengths vs. ages) were estimated using the Von Bertalanffy growth model. No significant differences for fish growth rates or for the relation fish length vs. fish Hg concentrations were found among the different regions except for the three lakes of the Abitibi region where fish grow more slowly than in the other lakes. Major differences were observed for growth rates or lengths vs. Hg concentrations in the different walleye populations of each lake. For example, a 5-year-old walleye with the lowest growth rate will reach an average length of 325 mm, whereas the average length for a walleye with the highest growth rate is 550 mm. Predicted values of Hg concentrations in walleyes of a standardized length of 350 mm ranged from 0.17 to 0.79 ppm. When all walleye populations of the 12 lakes were considered together, growth rates were significantly correlated to Hg concentrations (r=0.9244; P<0.001). This suggests that faster-growing walleyes will have lower Hg concentrations than slower-growing fish at a given length. The growth rate as a biological factor dominates all other environmental factors to account for differences in Hg concentrations in walleye populations studied. Nevertheless, the minor differences in Hg concentrations observed in walleye taken from two separate arms of a single lake in the Temiscamingue region, Lake Desjardins, could not be explained by fish growth rates only and thus should be related to other environmental parameters.