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Nkx2.5 is a homeobox containg transcription factor that is conserved and expressed in organisms that form hearts. Fruit flies lacking the gene(tinman) fail to form a dorsal vessel, mice that are homozygous null for Nkx2.5 form small, deformed hearts, and several human cardiac defects have been linked to dominant mutations in the Nkx2.5 gene. If the levels of Nkx2.5 mRNA are experimentally increased during Xenopus heart development, hearts are enlarged. In addition, small, aberrant hearts are formed when Nkx2.5 protein is modified so that its DNA binding domain remains intact, but its activation domain is replaced with a repressor domain. Here we investigate the consequences of the overexpression of two truncated forms of Nkx2.5 that have been identified in humans with congenital heart defects, mRNAs encoding these mutations were injected into single cell Xenopus embryos, and their heart development was monitored. Our results indicate that the introduction of Nkx2.5 variants leads to aberrant heart formation, which is especially evident during inspection of the atria of the heart. This type of experiment may provide an approach to determining the functional consequences of expression of human genes linked to developmental defects.

Nkx2-5 is a homeobox containing transcription factor that is conserved and expressed in organisms that form hearts. Fruit flies lacking the gene (tinman) fail to form a dorsal vessel, mice that are homozygous null for Nkx2-5 form small, deformed hearts, and several human cardiac defects have been linked to dominant mutations in the Nkx2-5 gene. The Xenopus homologs (XNkx2-5) of two truncated forms of Nkx2-5 that have been identified in humans with congenital heart defects were used in the studies reported here. mRNAs encoding these mutations were injected into single cell Xenopus embryos, and heart development was monitored. Our results indicate that the introduction of truncated XNkx2-5 variants leads to three principle developmental defects. The atrial septum and the valve of the atrioventricular canal were both abnormal. In addition, video microscopic timing of heart contraction indicated that embryos injected with either mutant form of XNkx2-5 have conduction defects., ((c) 2007 Wiley-Liss, Inc.)

Xenopus laevis provides a number of advantages to studies on cardiovascular development. The embryos are fairly large, are easy to obtain, and can develop at ambient temperature in simple buffer solutions. Although classic descriptions of heart development exist, the ability to use whole-mount immunohistochemical methods and confocal microscopy may enhance the ability to understand both normal and experimentally perturbed cardiovascular development. We have started to examine the early stages of cardiac development in Xenopus, seeking to identify antibodies and fixatives that allow easy examination of the developing heart. We have used monoclonal antibodies (mAbs) raised against bovine cardiac troponin T and chicken tropomyosin to visualize cardiac muscle, a goat antibody recognizing bovine type VI collagen to stain the lining of vessels, and the JB3 mAb raised against chicken fibrillin, which allows the visualization of a variety of cardiovascular tissues during early development. Results from embryonic stages 24-46 are presented., (Copyright 2000 Academic Press.)

We conducted a follow-up study of surgical cases of posterior subcapsular cataracts and their controls to evaluate the possible association of alcohol intake and posterior subcapsular opacities. Two hundred thirty-eight cases and controls were interviewed. Current alcohol intake and usual and maximum weekly consumption ever were assessed. In this population, 57% of the cases and 56% of the controls were nondrinkers, 22% of the cases and 36% of the controls had an average of seven or fewer drinks per week, and 17% of the cases and 8% of the controls had more than seven drinks per week. A matched pair analysis controlling for other known risk factors showed an increased risk associated with heavy alcohol use. Heavy drinkers were more likely to be cases than were nondrinkers (odds ratio, 4.6; P < .05), and light drinkers were not at an increased risk. This result suggests that heavy alcohol consumption may increase the risk of posterior subcapsular cataract.