The human Mis12 complex is required for kinetochore assembly and proper chromosome segregation.

During cell division, kinetochores form the primary chromosomal attachment sites for spindle microtubules. We previously identified a network of 10 interacting kinetochore proteins conserved between Caenorhabditis elegans and humans. In this study, we investigate three proteins in the human network (hDsn1Q9H410, hNnf1PMF1, and hNsl1DC31). Using coexpression in bacteria and fractionation of mitotic extracts, we demonstrate that these proteins form a stable complex with the conserved kinetochore component hMis12. Human or chicken cells depleted of Mis12 complex subunits are delayed in mitosis with misaligned chromosomes and defects in chromosome biorientation. Aligned chromosomes exhibited reduced centromere stretch and diminished kinetochore microtubule bundles. Consistent with this, localization of the outer plate constituent Ndc80HEC1 was severely reduced. The checkpoint protein BubR1, the fibrous corona component centromere protein (CENP) E, and the inner kinetochore proteins CENP-A and CENP-H also failed to accumulate to wild-type levels in depleted cells. These results indicate that a four-subunit Mis12 complex plays an essential role in chromosome segregation in vertebrates and contributes to mitotic kinetochore assembly.

Deciphering protein function during mitosis in PtK cells using RNAi.

BACKGROUND: Studying mitosis requires a system in which the dramatic movements of chromosomes and spindle microtubules can be visualized. PtK cells, due to their flat morphology and their small number of large chromosomes, allow microscopic visualizations to be readily performed. RESULTS: By performing RNAi in PtK cells, we can explore the function of many proteins important for spindle assembly and chromosome segregation. Although it is difficult to transfect DNA into PtK cells (efficiency approximately 10%), we have transfected a fluorescent siRNA at nearly 100% efficiency. Using a cDNA expression library, we then isolated a complete PtK MCAK (P-MCAK) cDNA. P-MCAK shares 81% identity to Human-MCAK (H-MCAK) protein and 66% identity to H-MCAK DNA. Knockdown of P-MCAK by RNAi caused defects in chromosome congression and defective spindle organization. Live imaging revealed that chromosomes had defects in congression and segregation, similar to what we found after microinjection of inhibitory anti-MCAK antibodies. Because it is laborious to isolate full-length clones, we explored using RT-PCR with degenerate primers to yield cDNA fragments from PtK cells from which to design siRNAs. We isolated a cDNA fragment of the mitotic kinesin Eg5 from PtK cells. This fragment is 93% identical to H-Eg5 protein and 87% identical to H-Eg5 DNA. A conserved 21 bp siRNA was used for RNAi in both HeLa and PtK cells in which Eg5 knockdown resulted in an increased mitotic index and cells with monopolar spindles. In addition, we used RT-PCR to isolate fragments of 5 additional genes, whose sequence identity ranged from 76 to 90% with human, mouse, or rat genes, suggesting that this strategy is feasible to apply to any gene of interest. CONCLUSION: This approach will allow us to effectively probe mitotic defects from protein knockdowns by combining genomic information from other organisms with the tractable morphology of PtK cells.

Healthy depictions? Depicting adoption and adoption news events on broadcast news.

Given that the public uses the media to learn about adoption as a family form, this study analyzes U.S. television news coverage of adoption between 2001 and 2005 (N = 309 stories), to identify the types of news events covered about adoption. A majority of news stories covered fraud, crime, legal disputes, and negative international adoption cases. Adoptees as defective or unhealthy were depicted more in negative news event stories, birth parents appeared less overall, and adoptive parents were most likely to have healthy depictions in positively oriented adoption experience, big family, and reunion stories. Although three quarters of the stories used primary adoption participants as news sources, one-third of the negative event stories did not contain healthy depictions of adoption participants. The authors discuss ways journalists and researchers might improve adoption news coverage.

Analysis of kinetochore assembly and function in Caenorhabditis elegans embryos and human cells.

All eukaryotes rely on multi-protein assemblies, called kinetochores, to direct the segregation of their chromosomes in mitosis. The list of known kinetochore components has been growing rapidly in the post-genomic era: in animal cells, there are presently more than 80 proteins that show either exclusive or partial localization at kinetochores during mitosis. The future challenge is to elucidate how these proteins contribute to kinetochore structure, spindle microtubule attachment, regulation of microtubule dynamics, and the detection, signaling, and correction of microtubule attachment errors. Cultured human tumor cells, especially HeLa cells, are widely used for the study of kinetochores. Recently, the experimental advantages offered by the nematode Caenorhabditis elegans have been exploited for functional analysis of kinetochore components in the first embryonic division. Here, we discuss basic methods, largely based on fluorescence imaging, to study kinetochore structure and function in these two metazoan model systems.