Final answer:
In eukaryotes, mRNA is called pre-mRNA before it gets fully processed. It undergoes several processing steps before leaving the nucleus as mature mRNA.
Step-by-step explanation:
In eukaryotes, before mRNA gets fully processed, it is called pre-mRNA. Pre-mRNA undergoes several processing steps including the addition of a 5' cap, splicing, editing, and 3' polyadenylation before it leaves the nucleus as mature mRNA.