mars and tousled-like kinase act in parallel to ensure chromosome fidelity in Drosophila.
BACKGROUND
High levels of Hepatoma Up-Regulated Protein (HURP) and Tousled-Like Kinase (TLK) transcripts are found in hepatocellular carcinoma. HURP overexpression induces anchorage-independent growth of 293-T cells and enhances a rough-eye phenotype resulting from tlk overexpression in Drosophila. In addition, both HURP and Mars, a Drosophila HURP sequence homologue, promote polymerization of mitotic spindles. Thus, the genetic interaction of mars with tlk might be required for accurate chromosome segregation.


METHODS
To reveal whether chromosome fidelity was decreased, the frequency of gynandromorphy, an individual with both male and female characteristics, and of non-disjunction were measured in the progeny from parents with reduced mars and/or tlk activities and analyzed by Student's t-test. To show that the genetic interaction between mars and tlk is epistatic or parallel, a cytological analysis of embryos with either reduced or increased activities of mars and/or tlk was used to reveal defects in mitotic-spindle morphology and chromosome segregation.


RESULTS
A significant but small fraction of the progeny from parents with reduced mars activity showed gynandromorphy and non-disjunction. Results of cytological analysis revealed that the decrease in chromosome fidelity was a result of delayed polymerization of the mitotic spindle, which led to asynchronous chromosome segregation in embryos that had reduced mars activity. By removing one copy of tousled-like kinase (tlk) from flies with reduced mars activity, chromosome fidelity was further reduced. This was indicated by an increased in the non-disjunction rate and more severe asynchrony. However, the morphology of the mitotic spindles in the embryos at metaphase where both gene activities were reduced was similar to that in mars embryos. Furthermore, tlk overexpression did not affect the morphology of the mitotic spindles and the cellular localization of Mars protein.


CONCLUSIONS
Chromosome fidelity in progeny from parents with reduced mars and/or tlk activity was impaired. The results from cytological studies revealed that mars and tlk function in parallel and that a balance between mars activity and tlk activity is required for cells to progress through mitosis correctly, thus ensuring chromosome fidelity.
Li
Hsing-Hsi
HH
Department of Life Sciences and Institute of Genome Sciences, National Yang-Ming University, Taipei, 112 Taiwan, ROC.
Chiang
Chuen-Sheue
CS
Huang
Hsiao-Yu
HY
Liaw
Gwo-Jen
GJ
D000595:Amino Acid Sequence; D000818:Animals; D002453:Cell Cycle; D020090:Chromosome Segregation; D002875:Chromosomes / Q000648:ultrastructure*; D029721:Drosophila Proteins / Q000096:biosynthesis / Q000502:physiology*; D004331:Drosophila melanogaster / Q000235:genetics / Q000378:metabolism*; D004843:Epistasis, Genetic; D005786:Gene Expression Regulation; D006801:Humans; D008954:Models, Biological; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000096:biosynthesis / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases / Q000096:biosynthesis / Q000502:physiology*; D017434:Protein Structure, Tertiary; D000074407:SAP90-PSD95 Associated Proteins; D017386:Sequence Homology, Amino Acid; D008941:Spindle Apparatus
D029721:Drosophila Proteins; C000614192:Mars protein, Drosophila; D009419:Nerve Tissue Proteins; D000074407:SAP90-PSD95 Associated Proteins; C498930:tlk protein, Drosophila; D017346:Protein Serine-Threonine Kinases