Drosophila DDP1, a multi-KH-domain protein, contributes to centromeric silencing and chromosome segregation.
BACKGROUND
The Drosophila melanogaster DDP1 protein is a highly evolutionarily conserved protein that is characterised by the presence of 15 tandemly organized KH domains, known for mediating high-affinity binding to single-stranded nucleic acids (RNA and ssDNA). Consistent with its molecular organization, DDP1 binds single-stranded nucleic acids with high affinity, in vitro. It was shown earlier that, in polytene chromosomes, DDP1 is found in association with chromocenter heterochromatin, suggesting a contribution to heterochromatin formation and/or maintenance.


RESULTS
In this paper, the actual contribution of DDP1 to the structural and functional properties of heterochromatin was determined through the analysis of the phenotypes associated with the hypomorphic ddp1(15.1) mutation that was generated through the mobilization of a P element inserted in the second intron of ddp1. ddp1(15.1) behaves as a dominant suppressor of PEV in the variegated rearrangement In(1)w(m4) as well as in several transgenic lines showing variegated expression of a hsp70-white(+) transgene. In polytene chromosomes from homozygous ddp1(15.1) larvae, histone H3-K9 methylation and HP1 deposition at chromocentre heterochromatin are strongly reduced. Our results also show that, when the maternal contribution of DDP1 is reduced, chromosome condensation and segregation are compromised. Moreover, in a ddp1(15.1) mutant background, transmission of the nonessential Dp1187 minichromosome is reduced.


CONCLUSIONS
We conclude that DDP1 contributes to the structural and functional properties of heterochromatin. These results are discussed in the context of current models for the formation and maintenance of heterochromatin; in these models, HP1 deposition depends on H3-K9 methylation that, in turn, requires the contribution of the RNAi pathway.
Huertas
Dori
D
Departament de Biologia Molecular i Cellular, Institut de Biologia Molecular de Barcelona, Consejo Superior de Investigaciones Científicas, Parc Científic de Barcelona, Josep Samitier, 1-5, 08028 Barcelona, Spain.
Cortés
Alfred
A
Casanova
Jordi
J
Azorín
Fernando
F
D000818:Animals; D030801:Animals, Genetically Modified; D002503:Centromere / Q000502:physiology*; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism; D020090:Chromosome Segregation / Q000502:physiology*; D003433:Crosses, Genetic; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D004331:Drosophila melanogaster / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D006570:Heterochromatin / Q000502:physiology*; D006657:Histones / Q000378:metabolism; D008745:Methylation; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D017434:Protein Structure, Tertiary; D034622:RNA Interference
D002868:Chromosomal Proteins, Non-Histone; D004268:DNA-Binding Proteins; C491076:Dp1 protein, Drosophila; D029721:Drosophila Proteins; D006570:Heterochromatin; D006657:Histones; C452193:heterochromatin protein 1, Drosophila