Research Group of Dr Marc-Jan Gubbels, Boston College, Massachusetts

Research Group of Dr Marc-Jan Gubbels, Boston College, Massachusetts

From left to right: Front row Katherine Cheng, Nivedita Sahoo, Courtney Cronin, Brooke Anderson-White, Seth Robertson, Alex Lorestani; back row: Marc-Jan Gubbels, Keith Eidell (not pictured: Tomasz Szatanek and Justin Rowinsky).

Dr Marc-Jan Gubbels is Assistant Professor at Boston College Massachusetts. Marc-Jan and his team is developing forward, reverse and functional genetic tools using enzymatic as well as fluorescent protein reporter assays, in combination with cell sorting and fluorescence microscopy, to learn more about the parasite’s cell biology.

Dr Marc-Jan Gubbels received his PhD in Tropical Veterinary Parasitology from the University of Utrecht in the Netherlands. Marc-Jan completed his post-doctoral research with Dr. Boris Striepen at the University of Georgia where he started working on Toxoplasma gondii. T. gondii is a protozoan parasite that causes disease in humans such as congenital retinochoroiditis and encephalitis in immunocompromised patients.

Congenital infection with the parasite T. gondii affects up to 1 in every 1000 pregnancies and manifests mostly in childhood as ocular toxoplasmosis, resulting in lesions of the retina, which in turn leads to vision reduction loss in the affected eye. Furthermore, the uncontrolled proliferation of the parasite in patients on immuno-suppressants as well as AIDS patients can lead to life-threatening encephalitis. Through his research Marc-Jan has enhanced the understanding of how the parasite divides, which he hopes will enable him to highlight new specific drug targets.

Pathogenesis caused by T.gondi coincides with the parasite going through the lytic cycle, either in a primary infection, or as the result of a relapsing chronic infection. This stage is characterized by repeated host-cell invasion, establishment of the parasitophorous vacuole, and replication within the host cell. Parasite proliferation can potentially be inhibited by intervention at each of these steps. The team’s goal is to enhance the knowledge about the specific biology of parasite invasion as well as its replication. These processes are at the core of parasitic behavior and are being investigated using the power of genetics. The advantage of this approach is the un-biased identification of genes involved in these processes.

Marc-Jan’s team has produced detailed research into parasite replication. The parasite replicates by an internal budding process, where two new daughter parasites are assembled within the mother. The complex cytoskeleton, which also anchors the motility, serves as a scaffold for daughter assembly. The cytoskeleton is composed of three basic elements: flattened membrane vesicles (cisternae) in complex with a set of microtubuli and a meshwork of intermediate filaments. This structure is known as the inner membrane complex IMC.

Recently Marc-Jan’s team has used Volocity to analyze several temperature sensitive mutants with defects in division with fluorescent protein reporter fusions and specific antibodies against the division and cytoskeletal components. A common phenotype is mitotic failure, where the parasites enter the next cell cycle without completing cytokinesis. After several rounds large cytoplasmic masses with big nuclei are observed. Multiple centrosome pairs are observed around these nuclei, and small new daughter cytoskeletons are formed in close approximation to the centrosomes. The formation of new daughter parasites takes cues from the number and location of the centrosomes.

Marc says “We specifically choose Volocity for its ease of use, so that there is a very low threshold for new users to use the microscope and take pictures or movies, in particular novice undergraduate students.”

If you would like to learn more about the Gubbels group research into the cell biology of T. gondii please visit his website.

Comparison of division and cell cycle progress of wild type (left panel) and a temperature sensitive division mutant displaying mitotic failure (right panel). Centrosome pairs are observed in association with the nuclei and are being packaged in new daughter cytoskeletons in wild-type (note the lower left parasite forms four instead of two parasites, corresponding with four centrosomes). The mutant panel shows a parasite that underwent one nuclear division where the lower nucleus did not retain a centrosome. The top nucleus has several centrosome pairs and several IMC buds are observed around this nucleus, but not around the nucleus without centrosomes. The extended focus feature of Volocity is very nice tool to immediately see how many centrosomes are present.