title: C. elegans HAM-1 functions in the nucleus to regulate asymmetric neuroblast division.
abstract: All 302 neurons in the C. elegans hermaphrodite arise through asymmetric division of neuroblasts. During embryogenesis, the C. elegans ham-1 gene is required for several asymmetric neuroblast divisions in lineages that generate both neural and apoptotic cells. By antibody staining, endogenous HAM-1 is found exclusively at the cell cortex in many cells during embryogenesis and is asymmetrically localized in dividing cells. Here we show that in transgenic embryos expressing a functional GFP::HAM-1 fusion protein, GFP expression is also detected in the nucleus, in addition to the cell cortex. Consistent with the nuclear localization is the presence of a putative DNA binding winged-helix domain within the N-terminus of HAM-1. Through a deletion analysis we determined that the C-terminus of the protein is required for nuclear localization and we identified two nuclear localization sequences (NLSs). A subcellular fractionation experiment from wild type embryos, followed by Western blotting, revealed that endogenous HAM-1 is primarily found in the nucleus. Our analysis also showed that the N-terminus is necessary for cortical localization. While ham-1 function is essential for asymmetric division in the lineage that generates the PLM mechanosensory neuron, we showed that cortical localization may not required. Thus, our results suggest that there is a nuclear function for HAM-1 in regulating asymmetric neuroblast division and that the requirement for cortical localization may be lineage dependent.
authors.affiliation: Department of Molecular Biology and Biochemistry Simon Fraser University, Burnaby, BC, Canada.
authors.forename: Amy
authors.initials: A
authors.lastname: Leung
authors.affiliation: Department of Molecular Biology and Biochemistry Simon Fraser University, Burnaby, BC, Canada.
authors.forename: Khang
authors.initials: K
authors.lastname: Hua
authors.affiliation: Department of Internal Medicine, University of Iowa, Iowa City, IA, USA.
authors.forename: Pavitra
authors.initials: P
authors.lastname: Ramachandran
authors.affiliation: Department of Molecular Biology and Biochemistry Simon Fraser University, Burnaby, BC, Canada.
authors.forename: Kyla
authors.initials: K
authors.lastname: Hingwing
authors.affiliation: Department of Molecular Biology and Biochemistry Simon Fraser University, Burnaby, BC, Canada.
authors.forename: Maria
authors.initials: M
authors.lastname: Wu
authors.affiliation: Department of Molecular Biology and Biochemistry Simon Fraser University, Burnaby, BC, Canada.
authors.forename: Pei Luan
authors.initials: PL
authors.lastname: Koh
authors.affiliation: Department of Molecular Biology and Biochemistry Simon Fraser University, Burnaby, BC, Canada. Electronic address: nhawkins@sfu.ca.
authors.forename: Nancy
authors.initials: N
authors.lastname: Hawkins
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D060049:Asymmetric Cell Division; D017173:Caenorhabditis elegans / Q000166:cytology / Q000502:physiology*; D029742:Caenorhabditis elegans Proteins / Q000502:physiology*; D019070:Cell Lineage; D002467:Cell Nucleus / Q000502:physiology*; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000502:physiology*; D058953:Neural Stem Cells / Q000502:physiology*; D009474:Neurons / Q000166:cytology / Q000502:physiology*
chemical_list: D029742:Caenorhabditis elegans Proteins; C103072:HAM-1 protein, C elegans; D009419:Nerve Tissue Proteins
keywords: Asymmetric cell division; C. elegans; Neuroblast; Nuclear localization; ham-1