Neonatal mortality and leanness in mice lacking the ARID transcription factor Mrf-2

Proteins containing the ARID (AT-rich interaction domain) DNA-binding motif regulate gene expression and differentiation in fungi, plants, and animals. This report describes phenotypes resulting from targeted disruption of the ARID gene Mrf-2. Homozygous loss of Mrf-2 resulted in a high rate of neonatal mortality that was partially strain-dependent: survival of Mrf-2(-/-) pups ranged from 6.4% on the 129S1 genetic background to 38% on a mixed 129S1.C57Bl/6J background. Loss of Mrf-2 expression did not affect embryonic survival, embryonic growth or birth weight. Lipid accumulation was severely reduced in brown adipose of Mrf-2(-/-) neonates at 24h of age, however, and Mrf-2(-/-) mice weighed significantly less than controls from postnatal day five onward. Adult Mrf-2(-/-) mice were lean, with significant reductions in brown and white adipose tissues, and in the percentage of body fat. Mrf-2(-/-) and Mrf-2(+/-) mice were also resistant to weight gains and obesity when maintained on high-fat diets. These phenotypes suggest that Mrf-2 is essential for accumulation of lipid stores in postnatal life.     

Expression of Brachyury-like T-box transcription factor, Xbra3 in Xenopus embryo

The Xenopus Brachyury-like Xbra3 gene is a novel T-box gene that is closely associated with Xenopus Brachyury. The expression pattern of Xbra3 during development is similar to that of Xbra. During gastrulation Xbra3 is expressed in the marginal zone, with a gradient of increasing expression from ventral to dorsal. In the early neurula stage Xbra3 is expressed in the notochord and posterior mesoderm, but by the tailbud stage its expression is restricted to the forming tailbud and the posterior portion of the notochord.