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FOXL2 is a member of the forkhead box family, a transcription factor essential for the early regulation of ovarian development that is expressed in a sexually dimorphic manner in vertebrates. However, data on this gene in invertebrates are rare. In this study, we cloned a full-length cDNA sequence of foxl2 from the scallop Chlamys farreri, an important commercial mollusk in China. The cDNA sequence of Cf-foxl2 (C. farreri foxl2) has 1,824 bp with an open reading frame of 1,107 bp encoding 369 amino acid residues containing the conserved domain forkhead box. Semiquantitative RT-PCR showed that Cf-foxl2 was expressed mainly in the ovary. Using quantitative real-time PCR, we found that the highest expression was in the ovary of proliferative stage animals, about 62-fold higher than that in the testis and about twofold higher than that in the ovary of growing and mature stages. In situ hybridization revealed that Cf-foxl2 mRNA was located in the cytoplasm of follicle cells and germ cells in the ovary and testis except in the spermatozoa. Our data imply that Cf-foxl2 is expressed in a sexually dimorphic pattern at the RNA level, which is conserved with vertebrates.

A Zhikong scallop (Chlamys farreri Jones and Preston 1904) tryptophan 2,3-dioxygenase (TDO) gene fragment, down-regulated by Vibrio anguillarum challenge, was isolated using mRNA di¡erential display in our previous work. In this paper, the full-length TDO gene was cloned by 5 0 -RACE. Chlamys farreri TDO gene consists of 1292 nucleotides encoding an expected polypeptide of 383 amino acids with an estimated molecular weight of 44.8 kDa and an isoelectric point of 6.35. The deduced amino acid sequence is 54^61% homologous to TDOs from Caenorhabditis elegans, Mus musculus, Danio rerio, Homo sapiens and Drosophila melanogaster, and shares several histidine residues important for the enzyme function in other species. Chlamys farreri TDO is expressed in the mantle, gill, digestive gland, testis, adductor muscle and kidney. Immunohistochemical analysis showed that C. farreri TDO was located mainly in the cytoplasm of most cell types. The non-speci¢c distribution of C. farreri TDO suggests that it is involved in various cellular processes.

With the increase of available protein-protein interaction (PPI) data, more and more efforts have been put to PPI network modeling, and a number of models of PPI networks have been proposed. Roughly speaking, good models of PPI networks should be able to accurately describe PPI mechanisms, and thus reproduce the structures of PPI networks. With such models, theoretical and/or computational biologists can efficiently explore the evolution and dynamics of PPI networks. However, a theoretical and/or computational biologist may feel confused when she/he has to choose a proper PPI model for her/his research work from a dozen of candidate models, while there is no guideline available to help her/him. To tackle this problem, in this article, we carry out a comprehensive performance comparison study on 12 existing models over PPI datasets of four species (yeast, mouse, fruit fly and nematode), by comparing the global and local statistical properties of the original PPI networks and the model-reproduced ones. To draw more convincing conclusions, we use the mean reciprocal rank to combine the ranks of a certain model on all statistical properties. Our experimental results indicate that the PS_Seed model [Solé and Pastor-Satorras (PS) model with seed] the STICKY model and the DD_Seed model (Duplication-Divergence model with seed) fit best with the test PPI datasets. By analyzing the underlying mechanisms of the models with better fitting ability, our analysis shows that the evolutionary mechanism of node duplication and link dynamics and the mechanisms with 'degree-weighted' behaviors seem to be able to describe the PPI networks better.

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