Novel nucleolar protein, midnolin, is expressed in the mesencephalon during mouse development

Using the gene trap method and the selection of embryonic stem cells in vit ro, we have identified several novel genes involved in mouse development. T he detailed analysis of one of these, named midnolin (midbrain nucleolar pr otein), is reported here. Expression of the midnolin gene is developmentall y regulated: it is strongly expressed at the mesencephalon (midbrain) of th e embryo in day 12.5 ((12.5) mice. The midnolin encodes a protein of 508 am ino acids (aa), which contains a Ubiquitin-like domain. The intracellular d istribution of the midnolin was studied by using midnolin-green fluorescent protein (GFP) fusion proteins. Midnolin was found to be localized in the n ucleus and nucleolus, but not in the cytoplasm. The nucleolar localization signal was determined to be a 28 aa peptide (440-QQKRLRRKARRDARGPYHWTPSRKAG RS-467) located at the C-terminal region of the midnolin, Our results sugge st that midnolin is involved in regulation of genes related to neurogenesis in the nucleolus. (C) 2000 Elsevier Science B.V. All rights reserved.