Inequality and collaboration in north China urban agglomeration: Evidence from embodied cultivated land in Jing-Jin-Ji's interregional trade.

An urban agglomeration is a highly connected city group, which is nested in complex trading networks. Ignoring the intercity connections and regional inequality may lead to the unsustainability of the urban agglomeration. The misuse and overuse of cultivated land resources are threatening environmental sustainability and causing global climate change. Facing the inequality and environment pressures in the urban agglomeration, the cultivated land resource reallocation within the complex urban agglomeration trading network should be systematically explored. This study analyzes the virtual cultivated land flows of the Jing-Jin-Ji (JJJ) region embodied in China's interregional trade network using a multiregional input-output model. Results show that the average virtual cultivated land intensity of the JJJ region is 1.59 ha/million yuan, which is below the national average. The JJJ region has 10.74 million ha of embodied cultivated land in consumption, accounting for 7.82% of the country's total amount. JJJ region is an import-oriented region and it receives virtual cultivated land from surrounding underdeveloped regions, such as Heilongjiang and Inner Mongolia. Beijing and Tianjin are typical net importers of virtual cultivated land, while Zhangjiakou, Xingtai, Hengshui, Baoding, and Cangzhou are net exporters in the interior of the JJJ region. This study could provide a systematical perspective and data supporting system for formulating the sustainable cultivated land use policies and collaborated development policies in the JJJ region to mitigate regional inequality. Policy suggestions concerning the eco-compensation mechanism, collaborative innovation mode, and uniform management platform in JJJ are given.

Roles of GATA6 during Gonadal Development in Japanese Flounder: Gonadogenesis, Regulation of Gender-Related Genes, Estrogen Formation and Gonadal Function Maintenance.

GATA-binding protein 6 (GATA6), a highly-conserved transcription factor of the GATA family plays an important role in gonadal cell proliferation, differentiation and endoderm development. In this study, the full-length cDNA of GATA6 of Paralichthys olivaceus (Japanese flounder) was obtained. Phylogenetic, gene structure and synteny analyses demonstrated that GATA6 of P. olivaceus is homologous to that of teleosts and tetrapods. The P. olivaceus GATA6 transcript showed higher expression in testis than in ovary, demonstrating a sexually dimorphic gene expression. During embryonic development, the expression of P. olivaceus GATA6 increased at the blastula stage, demonstrating that GATA6 is involved in morphogenesis. Results of in situ hybridization showed that GATA6 signals were detected in Sertoli cells, oogonia and oocytes. Moreover, 17α methyl testosterone, a male hormone, could moderately upregulate P. olivaceus GATA6 and downregulate P. olivaceus aromatase CYP19A1 in testis cells. These results suggest that GATA6 may play an important role in gonadal development in P. olivaceus. This study provides valuable information on the function of P. olivaceus GATA6, laying the foundation for further development of breeding techniques in this species.

Characterization of kiss2 and kissr2 genes and the regulation of kisspeptin on the HPG axis in Cynoglossus semilaevis.

Reproduction allows organisms to produce offspring. Animals shift from immature juveniles into mature adults and become capable of sexual reproduction during puberty, which culminates in the first spermiation and sperm hydration or ovulation. Reproduction is closely related to the precise control of the hypothalamic-pituitary-gonadal (HPG) axis. Kisspeptin peptides are considered as the important regulator of HPG axis in mammalian. However, the current understanding of kisspeptin in flatfish is not comprehensive. In this study, we cloned and analyzed the kiss2 and kissr2 genes in Cynoglossus semilaevis. Interesting alternative splicing in the 5'-untranslated regions (UTR) of the Cskissr2 gene was found. The expression profiles of Cskiss2 and Cskissr2 showed relative high messenger RNA (mRNA) levels at the late gastrula stage during embryonic development, at total length = 40 mm during early gonadal differentiation, and in the brains and gonads of all investigated tissues. These results suggested that the kisspeptin system participated in embryogenesis and in the regulation of gonadal differentiation and development. Considering that the control and regulatory mechanisms of kisspeptin in the central reproductive axis are still unclear, we documented that the intramuscular injection of kisspeptin caused different sGnRH and cGnRH mRNA levels in a dose- and tissue-dependent manner. The mRNA expressions of FSH and LH were stimulated in the ovary and were inhibited in the testis under the kisspeptin treatments. These results provided foundations for understanding the roles of kisspeptin in the neuroendocrine system in fish. The manipulation of the kisspeptin system may provide new opportunities to control the gonadal development and even reproduction in fish.

Identification and characterization of kiss2 and kissr2 homologs in Paralichthys olivaceus.

The role of kisspeptin in puberty onset has been extensively investigated by neuroendocrinologists in the past decade. In the present study, we first cloned and analyzed Pokiss2 and Pokissr2 genes in Paralichthys olivaceus, a Pleuronectiformes fish. By 5'/3' rapid amplification of cDNA ends (RACE), the P. olivaceus kiss2 gene (Pokiss2) and two isoforms of the P. olivaceus kissr2 gene (Pokissr2) transcripts were cloned. During development, Pokissr2 was maternally inherited but Pokiss2 was not, and their expression reached maximum and minimum levels, respectively, when the gonads began to develop. Analysis of tissue distribution revealed that Pokiss2 and Pokissr2 transcripts were predominantly expressed in the brain and gonads, with expression levels in females higher than those in males. Moreover, Pokiss2 and Pokissr2 both showed significantly higher expression in brains and gonads during puberty. In situ hybridization of the ovary at pre-vitellogenesis stage and testis at spermatogonial proliferation stage revealed that both Pokiss2 and Pokissr2 were expressed in spermatocyte, oocytes, and some somatic cells. Our results also showed significantly stronger Pokiss2 expression in the area of the third ventricle of females than males and no Pokissr2 expression in this region in both sexes. These results lay a strong foundation for understanding the role of kisspeptin in neuroendocrine system in teleosts, in particular in Pleuronectiformes.

Native recombinant kisspeptin can induce gnrh1 and kissr2 expression in Paralichthys olivaceus in vitro.

Kisspeptins have been described as one of the most potent activators of the hypothalamic-pituitary-gonadal axis. Kisspeptins control the onset of reproductive functions during puberty by directly stimulating the neuronal activity and release of gonadotropin-releasing hormone (GnRH). The function of kisspeptins has been investigated in vivo and in vitro. In our study, three kinds of recombinant kisspeptin proteins were expressed in Escherichia coli. Kisspeptin fragments Kp54, Kp44, and Kp10 translated from Paralichthys olivaceus kiss2 gene were then obtained. Kp44 contained 44 amide acids (aa) which are the same as the N-terminal of Kp54; Kp10 shares the same 10 aa with the C-terminal of Kp54 but Kp10 also contains some other amide acids. In the dose course of treatments with prokaryotically expressed peptides, Kp54 and Kp10 could induce the expression of kissr2 and gnrh1; by contrast, Kp44 could not induce a similar expression. These results provided direct evidence that the core decapeptide of kisspeptin is necessary to ensure its biological functions. In the time course of the Kp54 treatments on two kinds of cultured brain cells, different patterns of kissr2 and gnrh1 mRNA suggested that the responses of these cells to kisspeptins depends on cell type and treatment duration. Thus, our research provided alternative methods to investigate the functions of kisspeptin in vitro and to detect biological activities; this research also established basis for kisspeptin applications in production processes.

Molecular characterization, origin, and evolution of teleost p68 gene family: Insights from Japanese flounder, Paralichthys olivaceus.

Two rounds of whole-genome duplication occurred in the common ancestor of vertebrates. Later, a third round genome duplication occurred in the teleost fishes. As a prototype member of DEAD-box RNA helicases, the function of p68 helicase in development has been well investigated in human, however, limited information is available regarding the regulatory function of this gene in the development of teleosts. In this study, being an important farmed fish in North China, Japanese flounder (Paralichthys olivaceus) was used as model fish to investigate the role of p68 gene in teleost development. Two p68 genes were first identified from Japanese flounder. Molecular characterization of them was performed by analyzing the exon-intron boundaries. Then, we confirmed that such two teleost p68 genes originated from teleost-specific genome duplication through phylogenetic and synteny analyses. Additionally, comparative analyses of amino acid sequences, variation in selective pressure, and expression profiles of p68 genes revealed probable sub-functionalization fate of teleost p68 genes after the duplication. Therefore, this study supplements the evolutionary properties of teleost p68 gene family and provides the groundwork for further studying the regulatory function of p68 genes in the development of teleosts.