Studies Of Gene Differential Expression In Dictyostelium Discoideum Cells

The social amoeba Dictyostelium discoideum which phagocytosis soil bacteria for food is a unicellular eukaryote. Under favorable condition, it multiplies as a unicellular organism. Upon starvation, a pathway involving aggregation, mound, slug, culmination stages induces the formation of a fruiting body consisting of a head of spores supported on a stalk of vacuolated cells. Spores await dispersal and germinate in favourable conditions for amoeboid growth. Cells of Dictyostelium discoideum are triggered to undergo development when they have depleted their food source. During the early hours of development , Cell adhesion molecules play an important role in maintaining the on integrity of cell aggregation and influence subsequent cell—type differentiation and cell sorting. gp150 is normally first expressed at the loss aggregation stage and this adhesion molecule is important for development. 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. The hereditary information is carried on 6 chromosomes with sizes ranging from 4 to 8 Mb resulting in a total of about 34 Mb of DNA, The estimated number of genes in the genome is 11000 and many of the known genes show a high degree of sequence similarity to homologues in vertebrate species. Relative to vertebrate species ,the genome ,whch is (AtT)-rich (77%),has less intron. and has a broadly uniform composition. On a finer scale, nucleotide composition tracks the distribution of exons. 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. AK127 cells eventually dissociate into single cell. In addition, cell-type differentiation is blocked in these mutant cells. It is likely that gp150 plays a regulatory role in the the initial multicellular development.gp150 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 intracellularenzyme-catalyzed reactions and activing expression of genes needing for development.mRNA differential display was used to analyse the differences of gene expression between the wild strain KAx-3 cells and the mutant strain AK127 cells to study the influence of the cell adhesion molecule gp150 on the expression of genes needing for D.discoideum development. Total RNA was isolated from KAx-3 cells and AK127 cells developed for 121k 14h and 16h. After the reverse transcription and PCR reaction, distinct differential fragments could be seen on 1.5% agarose gel. The characteristic differential bands were recovered and cloned. Northern analysis recognized the three differential cDNA fragments, named D12A, D16Band d16a, respectively specific for the 12h and 16h of development. dl6a was gone with 5'RACE-PCR reaction. We expect to get the full distance of the d16a.Conclusion: D12A may be a novel gene in D. discoideum development. The protein of D16Bmay be Dictyostelium discoideum hypothetical protein,but we don't know the function of this protein. We need to further study the function of this protein. 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.The data are suggested that these genes should be involved in the D. discoideum development, which is also suggested that gp150 play an very important role in the development of D. discoideum.