Following TUBG into unexpected places
One area that particularly caught our attention was the relationship between TUBG and chromatin.
Centromeres are specialized chromosomal regions that help ensure accurate chromosome segregation. When this process fails, chromosomes or chromosome fragments can become trapped outside the main nucleus and form micronuclei. These structures are more than passive remnants of segregation errors: their DNA remains part of the cell’s genome, but replication and cell-cycle coordination within micronuclei are often disturbed, contributing to replication stress and genomic instability.
The story began during my postdoctoral work, when we first noticed an association between TUBG and chromatin while studying the TUBG-S131D mutant. At the time, this was unexpected. TUBG was still viewed primarily in terms of centrosomes and microtubule nucleation, so rather than dismissing the observation as an oddity, we decided to follow it.
That decision led us to explore the nuclear functions of TUBG. We found that TUBG helps coordinate reassembly of the nucleus around chromatin after mitosis and that its C-terminal DNA-binding region is important for this process. Our previous work had shown that TUBG is required for PCNA recruitment to origins of DNA replication. Another clue came from ChIP-seq, where TUBG was repeatedly associated with centromeric regions. Together, these observations made it increasingly difficult to view the chromatin connection as an isolated finding and led us to ask whether the TUBG meshwork might have a broader role in centromere dynamics and micronuclear organization.
Watching the process unfold
This is where the project changed for us. Live-cell imaging allowed us to move from asking where TUBG was located to watching how TUBG-containing structures behaved over time.
In living cells, we observed dynamic associations between TUBG-containing structures and centromeres, suggesting a relationship between the TUBG meshwork and centromere positioning and dynamics. For me, this was one of the points at which the study became conceptually more interesting than we had initially expected. It raised a broader possibility: could TUBG, best known for organizing microtubules at the centrosome, also help connect cytoplasmic organization with the spatial organization of chromatin inside the nucleus?
Our observations do not establish such a causal connection, but they raise the possibility that centrosomal organization and nuclear architecture are more closely connected than traditionally assumed.
The micronuclear observations were equally intriguing. TUBG accumulated within or around micronuclei, and time-lapse imaging revealed that the signal was not static: TUBG, DNA and replication-associated signals changed together over time in what appeared to be a kind of pas de deux. This shifted our question from simply asking where TUBG was located to asking what these dynamics might mean for micronuclear organization.
Given our previous finding that TUBG is required for PCNA recruitment to origins of DNA replication, the micronuclear observations raise a particularly interesting question about how replication is organized in this compartment. However, live-cell imaging alone cannot tell us whether TUBG directly determines micronuclear stability, replication or fate. What the movies reveal is a dynamic organizational relationship that now needs to be understood mechanistically.
Thinking about TUBG differently
Over time, these observations have changed the way we think about TUBG. We increasingly see it not only as a centrosomal microtubule-nucleating protein, but as part of a broader cellular meshwork with functions across several compartments.
Taken together with our earlier findings in chromatin, DNA replication and mitochondrial organization, the centromere and micronuclear observations add another dimension to a growing picture of TUBG as an organizer of cellular architecture. They also raise the possibility that TUBG-containing structures participate in coordinating cellular organization across compartments.
This may be particularly relevant in cancer biology, where chromosome segregation errors, micronuclei and genomic instability are common. But beyond cancer, these findings have reinforced a question that increasingly shapes how we think about cell biology: how do cellular structures work together rather than function as isolated components?
More questions than answers
As often happens in research, the study has generated new questions. What molecular interactions connect TUBG-containing structures to centromeres? Can centrosomal TUBG organization influence centromere positioning or other aspects of nuclear architecture? Does the role of TUBG in PCNA recruitment contribute to the coordination of DNA replication within micronuclei? And are these relationships different in normal and transformed cells?
These questions are among the most stimulating outcomes of the study and provide a clear direction for what we want to explore next.
Why the movies matter
The movies were important not only for communicating the work, but also for how we understood it. Static images showed TUBG, DNA and replication-associated proteins occupying related regions within micronuclei; live imaging revealed that these relationships changed over time.
Cells are not static systems. Their structures continuously assemble, remodel and interact, and sometimes simply watching these processes unfold can reveal relationships that are difficult to appreciate from fixed-cell experiments alone. In this project, watching was not simply a way of illustrating the result—it helped generate the questions.
Looking ahead
TUBG was discovered because of its fundamental role in microtubule nucleation, and that function remains central to cell biology. But a protein’s best-known function does not necessarily define the limits of its biology.
Our work over the years increasingly points toward TUBG as part of a broader structural system whose functions extend across cellular compartments. Together with emerging evidence for other non-canonical functions of TUBG, the centromere and micronuclear observations encourage us to ask how far this organizing role extends and how these different functions are coordinated.
What started for us as an unexpected association between TUBG and chromatin has therefore developed into a broader question about how cellular organization is coordinated across compartments.
Sometimes, looking at a familiar protein from a different perspective reveals unexpectedly unfamiliar biology.