Biomedical subjects

P Hatzopoulos

Publications and source records attributed to P Hatzopoulos.

24 records · Page 2Linked to original sources

PubMed1988

Developmental regulation of embryonic genes in plants.

Somatic embryogenesis from cultured carrot cells progresses through successive morphogenetic stages termed globular, heart, and torpedo. To understand the molecular mechanisms underlying plant embryogenesis, we isolated two genes differentially expressed during embryo development. The expression of these two genes is associated with heart-stage embryogenesis. By altering the culture conditions and examining their expressions in a developmental variant cell line, we found that these genes were controlled by the developmental program of embryogenesis and were not directly regulated by 2,4-dichlorophenoxyacetic acid, the growth regulator that promotes unorganized growth of cultured cells and suppresses embryo morphogenesis. These genes are also expressed in carrot zygotic embryos but not in seedlings or mature plants.

Journal Article↗

PubMed1987

hobo is responsible for the induction of hybrid dysgenesis by strains of Drosophila melanogaster bearing the male recombination factor 23.5MRF.

The male recombination factor 23.5MRF, isolated ten years ago from a natural Greek population of Drosophila melanogaster, has been shown to induce hybrid dysgenesis when crossed to some M strains, in a fashion slightly different from that of most P strains. Furthermore, it was recently shown that 23.5MRF can also induce GD sterility when crossed to specific P strain females (e.g., Harwich, pi 2 and T-007). In these experiments, the P strains mentioned behaved like M strains in that they did not induce sterility in the reciprocal crosses involving 23.5MRF. We extended the analysis to show that 23.5MRF does not destabilize snW(M) and that a derivative with fewer full-length P elements behaves like an M strain toward the same P strains and still retains its dysgenic properties in the reciprocal crosses. We show that there is a strong correlation between the site of dysgenic chromosomal breakpoints induced by 23.5MRF and the localization of hobo elements on the second chromosome, and also that hobo elements are found associated with several 23.5MRF induced mutations. These results suggest that hobo elements are responsible for the aberrant dysgenic properties of this strain, and that they may express their dysgenic properties independent of the presence of P elements.

Animals↗

PubMed1987

The instability of the TE-like mutation Dp(2:2)GYL of Drosophila melanogaster is intimately associated with the hobo element.

We have characterized molecularly several derivatives of the TE-like element Dp(2:2)GYL of Drosophila melanogaster. This highly unstable mutation occurred in a dysgenic cross involving the 23.5 MRF chromosome, and represents an inverted insertional duplication of approximately 130 polytene bands of the paternal 2L, at 50AB of the right arm of the maternal 2R. The instability of this mutation is characterized by deletion of some of duplicated material, by the induction of rearrangements in its vicinity and by the transposition of parts of the original element. We have found that the mobile element hobo is present at , or very near, the breakpoints of all GYL derivatives analysed, demonstrating that hobo is not only active in dysgenic crosses, but also that it can promote genetic instability reminiscent of transposable elements (TE).

Animals↗

PubMed1987

Differential and temporal expression of the vitellogenin genes in Drosophila grimshawi.

The three vitellogenin transcripts from Drosophila grimshawi have an average size of 1,600 nucleotides as determined using denaturing electrophoretic conditions. Southern analysis showed that the large quantity of vitellogenin mRNAs in adult female fat body cells is not a reflection of specific gene amplification. The quantitative differences in mRNA accumulation between fat body and follicle cells, which are in concert with the onset of their translation, indicate that vitellogenin synthesis entails the regulated expression of individual genes. The expression of the vitellogenin genes during follicle development is stage specific: V1 and V2 expression starts at late stage 7, while V3 is delayed by one stage. Maximum transcription of all three genes occurs at stage 10 whereas at stage 12 none of the transcripts is present. These results suggest that, either there is more than one regulatory signal, or there is one to which each gene reacts differently. Surprisingly, in male fat body cells a V2 transcript has been detected which is also present in the poly(A)+RNA fraction: the function and the purpose of this particular vitellogenin mRNA in male fat body cells are unknown. Neither of the other two vitellogenin transcripts have been detected in male fat body cells.

Adipose Tissue↗

PubMed1987

Isolation and structural analysis of Drosophila grimshawi vitellogenin genes.

We isolated recombinant genomic DNA clones containing sequences coding for the female-specific vitellogenin proteins of Drosophila grimshawi. By screening with cDNA vitellogenin clones derived from female fat body mRNA we were able to isolate all three genes, namely V1, V2 and V3. The identity of these genes was established first by cell-free translation of the hybrid-selected mRNA followed by protease digestion of the in vitro translation products and second by hybridization of the three genes to electrophoretically separated mRNAs. The transcriptional orientation of these genes was determined. The V1 and V2 genes have opposite orientations with their 5'-ends 1.75 kb apart. S1 analysis demonstrated that the V1 gene has three exons of 310, 400 and 980 bp in length and two introns of about 120 bp. The V2 gene has two exons of 300 and 1260 bp in length and an intron 100 bp long. The V3 gene has three exons of 250, 375 and 820 bp in length and two introns of about 120 bp. The homology, in both sequence and structure, of the vitellogenin genes indicates that they have arisen by duplication events from an ancestral gene. Moreover, the similarity of the V1 and V2 gene positions within the genome of the two distant species D. melanogaster and D. grimshawi suggests a functional coupling of these two genes during vitellogenin gene expression.

Animals↗

PubMed1986

Noncoordinate synthesis of the vitellogenin proteins in tissues of Drosophila grimshawi.

In analyzing the in vitro pattern of protein synthesis by the fat body and ovaries of the Hawaiian species Drosophila grimshawi, we have found that the ovaries synthesize much more protein than the female fat body and that the majority of the synthesized proteins are retained by the ovarian tissues. In contrast, the fat body secrets most of the proteins into the culture medium. Vitellogenins are the major class of proteins synthesized and released into the medium by both tissues. The synthesis of the three vitellogenin proteins (V1, V2, V3) is noncoordinate in the two tissues. Ovaries synthesize much more of the V2 protein, less V1 and very little V3, whereas fat body synthesizes more V1 protein with lesser quantities of the other two. The follicle cells were identified as the site of ovarian vitellogenin synthesis in D. grimshawi, confirming the findings in D. melanogaster. In D. grimshawi, the three vitellogenins are synthesized by the follicle cells in a noncoordinate and developmentally regulated manner. V2 and V1 are the predominant proteins at the onset of vitellogenesis (S8-9); their production peaks together with that of V3 a few hours later (S10) and then decreases to quantities equal to that of V3 during early choriogenesis (S11). During active choriogenesis (S12), V2 and V1 cease to be synthesized, but V3 synthesis continues. The vitellogenins synthesized by the follicles in vitro are released into the medium and not incorporated into the oocyte.

Adipose Tissue↗