| The social amoeba Dictyostelium discoideum is a lower eukaryote protozoan. The amoeboid cells grow as separate, independent cells feeding on bacteria by phagocytosis and multipling by equal mitotic division. Exhaustion of the food source triggers a development programme, in which more than 100,000 cells aggregate by chemotaxis to form a multicellular structure. Morphogenesis and cell differentiation then culminate in the production of spores, enabling the organism to survive unfavourable condictions. A wide range of fundamental cellular processes are common to D. discoideum and metazoans. These processes include cytokinesis> motility, phagocytosis, chemotaxis, signal transduction and aspects of development such as cell sorting, pattern formation and cell-type determination. Many of these cellular behaviors and biochemical mechanisms are either absent or less accessible in other model organisms, making D. discoideum unique model organism for the study of the cellular and molecular mechanisms of these processes.After food source is depleted, the wild-type strain KAX-3 undergoes chemotaxis, cell-aggregating stage, mound-formation stage, slug stage and forms normal fruiting-body in the end. However, the mutant-type strain AK127, as a result of absence of gpl50, undergoes normal chemotaxis, but is arrested at the loose aggregate stage. Aggregates of AK127 cells eventually dissociate into single cells. In addition, cell-type differentiation is blocked in these mutant cells. It is likely that gpl50 plays a regulatory role in the transition from the initial multicellular stage to the tight mound stage and in cell-type specification. gpl50 is a membrane glycoprotein which has been implicated in cell-cell adhesion and may function as a key molecule transferring signal between cells, further regulating intracellular enzyme-catalyzed reactions and activing expression of genes needing for development.To study the influence of the cell adhesion molecule gpl50 on the expression of genes needing for D. discoideum development, mRNA differential display was used to analyse the differences of gene expression between the wild strain KAX-3 cells and the mutant strain AK127cells. Total RNAs from KAX-3 cells and AK127 cells, developed for 12h, 14h and 16h, were isolated. After the reverse transcription and PCR reaction, distinct differential fragments could be seen on 1.5% agarose gel. The five characteristic differential bands were recovered and cloned. Northern analysis recognized the three differential cDNA fragments, named d12, d14a and d16a, respectively specific for the 12h, 14h and 16h of development. Sequence querying and comparing with nucleic acid and protein in NCBI data-base revealed dl2b is 131 bp in length, having low homology with other known genes and no high homology proteins found. dl4a is 602 bp in length, having low homology with other known genes. We found its translated amino acid sequence and confirmed it IgC2 by SMART. dl6a is 496 bp in length, having relatively high homology with D. discoideum mitochondrial ribosomal protein S4 (Dd- mtRPS4). Dd-mtRPS4 plays a pole in the transition of D. discoideum cells to differentiation, and mitochondrial also regulates D. discoideum development, participating in prespore cell differentiation during slug stage.Conclusion: dl2b may be a novel gene in D. discoideum development. The protein of dl4a may be IgC2, related to gpl30. dl6a may be a ORF of mitochondrial DNA and be involved in prespore cells differentiation.Next, we need to acquire cDNA whole sequence , design carrier to express protein and deeply identify their biological functions during D. discoideum development by experiment.
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