RESUMO
HORMA domain-containing proteins regulate interactions between homologous chromosomes (homologs) during meiosis in a wide range of eukaryotes. We have identified a mouse HORMA domain-containing protein, HORMAD1, and biochemically and cytologically shown it to be associated with the meiotic chromosome axis. HORMAD1 first accumulates on the chromosomes during the leptotene to zygotene stages of meiotic prophase I. As germ cells progress into the pachytene stage, HORMAD1 disappears from the synapsed chromosomal regions. However, once the chromosomes desynapse during the diplotene stage, HORMAD1 again accumulates on the chromosome axis of the desynapsed homologs. HORMAD1 thus preferentially localizes to unsynapsed or desynapsed chromosomal regions during the prophase I stage of meiosis. Analysis of mutant strains lacking different components of the synaptonemal complex (SC) revealed that establishment of the SC is required for the displacement of HORMAD1 from the chromosome axis. Our results therefore strongly suggest that also mammalian cells use a HORMA domain-containing protein as part of a surveillance system that monitors synapsis or other interactions between homologs.
Assuntos
Proteínas de Ciclo Celular/metabolismo , Pareamento Cromossômico/fisiologia , Cromossomos de Mamíferos/metabolismo , Meiose/fisiologia , Animais , Proteína BRCA1/metabolismo , Células COS , Proteínas de Ciclo Celular/química , Núcleo Celular/metabolismo , Chlorocebus aethiops , Proteínas Cromossômicas não Histona/genética , Proteínas Cromossômicas não Histona/metabolismo , Proteínas de Ligação a DNA , Embrião de Mamíferos/metabolismo , Feminino , Histonas/metabolismo , Masculino , Prófase Meiótica I/fisiologia , Camundongos , Camundongos Knockout , Proteínas Nucleares/genética , Proteínas Nucleares/metabolismo , Oócitos/metabolismo , Estágio Paquíteno/fisiologia , Isoformas de Proteínas/genética , Isoformas de Proteínas/metabolismo , Espermatócitos/metabolismo , Complexo Sinaptonêmico/metabolismo , Testículo/metabolismo , Transfecção , CoesinasRESUMO
Meiotic crossovers are produced when programmed double-strand breaks (DSBs) are repaired by recombination from homologous chromosomes (homologues). In a wide variety of organisms, meiotic HORMA-domain proteins are required to direct DSB repair towards homologues. This inter-homologue bias is required for efficient homology search, homologue alignment, and crossover formation. HORMA-domain proteins are also implicated in other processes related to crossover formation, including DSB formation, inhibition of promiscuous formation of the synaptonemal complex (SC), and the meiotic prophase checkpoint that monitors both DSB processing and SCs. We examined the behavior of two previously uncharacterized meiosis-specific mouse HORMA-domain proteins--HORMAD1 and HORMAD2--in wild-type mice and in mutants defective in DSB processing or SC formation. HORMADs are preferentially associated with unsynapsed chromosome axes throughout meiotic prophase. We observe a strong negative correlation between SC formation and presence of HORMADs on axes, and a positive correlation between the presumptive sites of high checkpoint-kinase ATR activity and hyper-accumulation of HORMADs on axes. HORMADs are not depleted from chromosomes in mutants that lack SCs. In contrast, DSB formation and DSB repair are not absolutely required for depletion of HORMADs from synapsed axes. A simple interpretation of these findings is that SC formation directly or indirectly promotes depletion of HORMADs from chromosome axes. We also find that TRIP13 protein is required for reciprocal distribution of HORMADs and the SYCP1/SC-component along chromosome axes. Similarities in mouse and budding yeast meiosis suggest that TRIP13/Pch2 proteins have a conserved role in establishing mutually exclusive HORMAD-rich and synapsed chromatin domains in both mouse and yeast. Taken together, our observations raise the possibility that involvement of meiotic HORMA-domain proteins in the regulation of homologue interactions is conserved in mammals.
Assuntos
Adenosina Trifosfatases/metabolismo , Proteínas de Ciclo Celular/metabolismo , Meiose , Complexo Sinaptonêmico/metabolismo , ATPases Associadas a Diversas Atividades Celulares , Adenosina Trifosfatases/genética , Animais , Proteínas de Ciclo Celular/genética , Pareamento Cromossômico , Quebras de DNA de Cadeia Dupla , Feminino , Masculino , Camundongos , Camundongos Endogâmicos C57BLRESUMO
Bacterial chromosomes (though not Escherichia coli and some other gamma-proteobacterial chromosomes) contain parS sequences and parAB genes encoding partitioning proteins, i.e. ParA (ATPase) and ParB (DNA-binding proteins) that are components of the segregation machinery. Here, mycobacterial parABS elements were characterized for the first time. parAB genes are not essential in Mycobacterium smegmatis; however, elimination or overexpression of ParB protein causes growth inhibition. Deletion of parB also leads to a rather severe chromosome segregation defect: up to 10% of the cells were anucleate. Mycobacterial ParB protein uses three oriC-proximal parS sequences as targets to organize the origin region into a compact nucleoprotein complex. Formation of such a complex involves ParB-ParB interactions and is assisted by ParA protein.