It's time for another HPA image of the week! This week we would like to tease an annotation that is not yet publicly available, but is coming soon in the December 4 release of the Cell Atlas.

During the cell cycle, each chromosome containing your DNA replicates. During mitosis, each chromosome lines up with its copy in the middle of the cell. At this point, the copies of each chromosome are pulled apart from each other via a structure called the mitotic spindle. In order for this chromosomal separation to happen correctly, the two copies of each chromosome must be attached to the microtubules via the kinetochore ( DeLuca J.G. et al 2002). This little protein structure anchors the chromosomes to the correct microtubules which then pull apart the chromosomes via the mitotic spindle so that the daughter cells correctly receive one full copy of your DNA.

In Figure 1 we see an image of the kinetochore protein INCENP (green) together with a DNA marker, DAPI (blue) and microtubules (red) in MCF-7 cells, a human adenocarcinoma cell. Localizing this protein gives us excellent insight into the remarkably specific function it has in the cell.

The kinetochore plays a major role in regulating microtubule dynamics during mitosis, and disorders in this structure can lead to severe disease (Bakhoum S.F. & Compton D.A. 2012). The process of chromosomal segregation can play a role in cancer progression, and INCENP has recently been linked to hereditary suseptability to certain types of breast cancers ( Kabisch M et al 2015). Interestingly, despite its importance, it appears that cells often incorrectly attempt microtubule attachment to the kinetochore before undergoing a correction phase to ensure proper chromosome segregation ( Kitajima T.S. et al 2011). This mechanism may provide more insight into how to target and treat related diseases.

At the end of mitosis (telophase), cells are just finishing dividing, and as they are pinched apart the "cytokinetic bridge" forms between the cells. The keen eyed observer may notice that INCENP also localizes to this structure as seen in the bottom center of the selected image however we will save discussion of this structure for another IOTW.

The kinetochore annotation along with several others will be available after the upcoming December 4th Cell Atlas release. We hope these refined annotations within the cell will aid researchers in understanding protein function. We would further like to thank all the members of the Cell Atlas team for their hard work leading up to the release!

Devin Sullivan