Prometaphase

Definition
noun
The phase of mitosis between prophase and metaphase wherein the nuclear envelope breaks down and form membrane vesicles, chromatin condenses forming chromatids, and kinetochore forms around the centromere
Supplement
Prometaphase is that phase in mitosis in between prophase and metaphase. It takes place after prophase and preceding metaphase of a dividing eukaryotic cell. However, prometaphase is sometimes considered as part of the prophase, particularly towards the end and prior to metaphase.
During this stage, the nuclear membrane breaks down and forms numerous membrane vesicles. The seeming disappearance of the nuclear envelope marks the beginning of prometaphase. The breakdown of the nuclear membrane allows the chromatin structures to condense and thicken into chromatids. Another highlight of the prometaphase is the formation of proteins into a kinetochore around the centromere. The kinetochore is important as it joins the sister chromatids at the central point (centromere). Kinetochore microtubules emerging from the centrosomes (which are located at opposite ends of a dividing cell) attach to the kinetochores. ¹ After the events of prometaphase is the next phase of mitosis, which is the metaphase.
Word origin: Latin or Greek pró (before) + metaphase
See also:

• prophase
• metaphase
• mitosis
• nuclear membrane
• chromatin
• chromatid
• chromosome
• kinetochore
• centromere
• microtubule
• cell division

Reference(s):

¹“prometaphase”. Nature Education. http://www.nature.com/scitable/definition/prometaphase-281