Two alloalleles of Xenopus laevis hairy2 gene--evolution of duplicated gene function from a developmental perspective.

Gene duplication is a fundamental source of a new gene in the process of evolution. A duplicated gene is able to accept many kinds of mutations that could lead to loss of function or novel phenotypic diversity. Alternatively, the duplicated genes complementarily lose part of their functions to play original roles as a set of genes, a process called subfunctionalization. Pseudotetraploid frog Xenopus laevis has four sets of genes, and it is generally thought that the alloalleles in X. laevis have mutually indistinguishable functions. In this paper, we report differences and similarities between Xhairy2a and Xhairy2b in the neural crest, floor plate, and prechordal plate. Knockdown studies showed that Xhairy2a seems not to function in the neural crest, although both of them are required in the floor plate and the prechordal plate. Temporal expression pattern analysis revealed that Xhairy2a is a maternal factor having lower zygotic expression than Xhairy2b, while Xhairy2b is not loaded in the egg but has high zygotic expression. Spatial expression pattern analysis demonstrated that future floor plate expression is shared by both alloalleles, but Xhairy2b expression in the neural crest is much higher than Xhairy2a expression, consistent with the results of individual knockdown experiments. Therefore, our data suggest that subfunctionalization occurs in Xhairy2.

Tissue-specific expression of pancreatic-type RNases and RNase inhibitor in humans.

The tissue-specific expression of five human pancreatic-type RNases and RNase inhibitor was analyzed by Northern hybridization against poly(A)+ RNA prepared from 16 normal tissues. The widespread expression of RNase 1 was observed in almost all of the tissues. RNase 4 and angiogenin showed a similar distribution of expression abundantly present in the liver. This suggested the identity of the cell types producing these two molecules. However, no relativity appeared to be present between the vascularization of the tissues and the angiogenin expression. A narrow range of expression of the eosinophil-derived neurotoxin gene was observed. This localization seems related to the phagocytic cells in the tissues. The undetectable level of the eosinophil cationic protein mRNA in normal tissues suggests that the differentiation of eosinophils, triggered by inflammation and/or atopy, is required. The expression of RNase inhibitor was found to be ubiquitous. The regulatory function of inhibitor against RNases in the cell should be considered in studying the physiological significance of the pancreatic-type RNase family.