In the lab, we use advanced live imaging technologies to follow the development of mammalian oocytes into fertilisable eggs. We routinely monitor the entire process of meiosis by dissecting ovaries and isolating oocytes in the presence of inhibitors that prevent their release from prophase arrest. This continued arrest in prophase outside the ovary affords us enough time to label microtubules and DNA so we can later on visualise the meiotic spindle and chromosomes in real time. To label these components, we microinject each oocyte with mRNAs encoding fluorescent variants of H2B (marks chromosomes) and MAP4 (marks microtubules). After about three hours of mRNA expression, we relieve the inhibition of meiotic maturation by simply transferring microinjected oocytes into culture media without inhibitors. We then perform high resolution or super-resolution live imaging of the meiotic spindle and chromosomes, now fluorescently-marked, using advanced confocal microscopes such as the one shown below. Importantly, these microscopes are fitted with environmental chambers that accurately control the temperature of the air surrounding the cells and therefore allow long-term live imaging of meiosis in mammalian oocytes.
Figure 1. Visualising meiosis. Firstly, ovaries are dissected and oocytes are isolated. Next, oocytes are microinjected with mRNAs encoding fluorescent labels of chromosomes and microtubules. After typically three hours of mRNA expression, oocytes are released from prophase arrest and placed on advanced live cell imaging microscopes to follow spindle assembly, relocation and chromosome segregation at high spatial and temporal resolution.
© Upper row – Binyam Mogessie