Identification of a novel human kinesin-related gene (HK2) by the cDNA differential display technique

Kif2a regulates spindle organization and cell cycle progression in meiotic oocytes

Kif2a is a member of the Kinesin-13 microtubule depolymerases. Here, we report the expression, subcellular localization and functions of Kif2a during mouse oocyte meiotic maturation. Immunoblotting analysis showed that Kif2a was gradually increased form GV to the M I stages, and then decreased slightly at the M II stage. Confocal microscopy identified that Kif2a localized to the meiotic spindle, especially concentrated at the spindle poles and inner centromeres in metaphase and translocated to the midbody at telophase. Kif2a depletion by siRNA microinjection generated severely defective spindles and misaligned chromosomes, reduced microtubule depolymerization, which led to significant pro-M I/M Iarrest and failure of first polar body (PB1) extrusion. Kif2a-depleted oocytes were also defective in spindle pole localization of γ-tubulin and showed spindle assembly checkpoint (SAC) protein Bub3 at the kinetochores even after 10 hr extended culture. These results demonstrate that Kif2a may act as a microtubule depolymerase, regulating microtubule dynamics, spindle assembly and chromosome congression, and thus cell cycle progression during mouse oocyte meiotic maturation.

Global discovery of erythroid long noncoding RNAs reveals novel regulators of red cell maturation

Erythropoiesis is regulated at multiple levels to ensure the proper generation of mature red cells under multiple physiological conditions. To probe the contribution of long noncoding RNAs (lncRNAs) to this process, we examined >1 billion RNA-seq reads of polyadenylated and nonpolyadenylated RNA from differentiating mouse fetal liver red blood cells and identified 655 lncRNA genes including not only intergenic, antisense, and intronic but also pseudogene and enhancer loci. More than 100 of these genes are previously unrecognized and highly erythroid specific. By integrating genome-wide surveys of chromatin states, transcription factor occupancy, and tissue expression patterns, we identify multiple lncRNAs that are dynamically expressed during erythropoiesis, show epigenetic regulation, and are targeted by key erythroid transcription factors GATA1, TAL1, or KLF1. We focus on 12 such candidates and find that they are nuclear-localized and exhibit complex developmental expression patterns. Depleting them severely impaired erythrocyte maturation, inhibiting cell size reduction and subsequent enucleation. One of them, alncRNA-EC7, is transcribed from an enhancer and is specifically needed for activation of the neighboring gene encoding BAND 3. Our study provides an annotated catalog of erythroid lncRNAs, readily available through an online resource, and shows that diverse types of lncRNAs participate in the regulatory circuitry underlying erythropoiesis.

KIF2Abeta: A kinesin family member enriched in mouse male germ cells, interacts with translin associated factor-X (TRAX)

Translin associated factor X (TRAX) is a binding partner of TB-RBP/Translin. A cDNA encoding the 260 C-terminal amino acids of KIF2Abeta was isolated from mouse testis cDNAs in a yeast two-hybrid library screen for specific TRAX-interacting proteins. KIF2Abeta was expressed predominantly in the mouse testis and enriched in germ cells. The interaction of full-length KIF2Abeta or its C-terminus with TRAX was verified using in vitro synthesized fusion proteins. Deletion mapping of the TRAX-binding region of KIF2Abeta indicated that amino acids 514-659 were necessary and sufficient for the interaction in vivo. Confocal microscopy studies using GFP-fusion proteins demonstrated that KIF2Abeta colocalizes with TRAX in a perinuclear location. KIF2Abeta does not interact with TB-RBP, suggesting that either TRAX can function as an adaptor molecule for motor proteins and TB-RBP, or that this interaction reveals an undescribed role for TRAX in germ cells. The interaction with KIF2Abeta suggests a role for TRAX in microtubule-based functions during spermatogenesis.

The KinI kinesin Kif2a is required for bipolar spindle assembly through a functional relationship with MCAK

Although the microtubule-depolymerizing KinI motor Kif2a is abundantly expressed in neuronal cells, we now show it localizes to centrosomes and spindle poles during mitosis in cultured cells. RNAi-induced knockdown of Kif2a expression inhibited cell cycle progression because cells assembled monopolar spindles. Bipolar spindle assembly was restored in cells lacking Kif2a by treatments that altered microtubule assembly (nocodazole), eliminated kinetochore–microtubule attachment (loss of Nuf2), or stabilized microtubule plus ends at kinetochores (loss of MCAK). Thus, two KinI motors, MCAK and Kif2a, play distinct roles in mitosis, and MCAK activity at kinetochores must be balanced by Kif2a activity at poles for spindle bipolarity. These treatments failed to restore bipolarity to cells lacking the activity of the kinesin Eg5. Thus, two independent pathways contribute to spindle bipolarity, with the Eg5-dependent pathway using motor force to drive spindle bipolarity and the Kif2a-dependent pathway relying on microtubule polymer dynamics to generate force for spindle bipolarity.

Unconventional motoring: an overview of the Kin C and Kin I kinesins

All kinesins share a conserved core motor domain implying a common mechanism for generating force from ATP hydrolysis. How is it then that kinesins exhibit such divergent activities: motility, microtubule cross-linking and microtubule depolymerization? Although conventional motile kinesins have served as the paradigm for understanding kinesin function, the unconventional kinesins exploit variations on the motile theme to perform unexpected tasks. This review summarizes the biological functions and examines the possible molecular mechanisms of Kin C and Kin I unconventional kinesins. We also discuss the possible differences between the microtubule destabilization models proposed for Kar3 and Kin I kinesins.

cDNA cloning, expression pattern, genomic structure and chromosomal location of RAB6KIFL, a human kinesin-like gene

Kinesin-like proteins are microtubule-associated motors that play important roles in intracellular transport and cell division. We report here the characterization of a new human kinesin-like protein, Rabkinesin6 (RAB6KIFL). The composite cDNA sequence is 2957bp, and encodes a protein of 890 amino acids with a predicted molecular weight of 100kDa. It has high homology (93% similarity) with the mouse kinesin-like protein, Rab6kifl, indicating that it is the human homologue of the mouse gene. RAB6KIFL has all of the structural characteristics required to function as a microtubule-associated motor. Unlike the mouse gene which is ubiquitously expressed, RAB6KIFL expression appears to be tissue specific. It is widely expressed in fetal tissues, abundantly expressed in adult thymus, bone marrow and testis, and is expressed at low levels in heart, placenta and spleen. The RAB6KIFL gene is mapped to human chromosome 5, band q31, spans approximately 8.5kb of genomic DNA, and contains 19 exons. RAB6KIFL maps within the smallest commonly deleted segment in myeloid leukemias characterized by a deletion of 5q; however, we detected no mutations of RAB6KIFL in malignant myeloid disorders with loss of 5q. The description of this human kinesin-like protein may provide a better understanding of the diversity of this large family of proteins.

Identification of 40 genes on a 1-Mb contig around the IL-4 cytokine family gene cluster on mouse chromosome 11

Five related cytokine genes, interleukin 3 (Il3), interleukin 4 (Il4), interleukin 5 (Il5), interleukin 13 (Il13), and granulocyte-macrophage colony-stimulating factor (Csfgm or Csf2), are tightly linked on mouse chromosome 11. We now describe a 1-Mb transcript map of this cytokine cluster. Genomic clones obtained by screening mouse bacterial artificial chromosome (BAC) and P1-derived artificial chromosome (PAC) libraries were subcloned into the pSPL3 expression vector and transfected into COS7 cells for exon trapping. In total, 118 distinct, putative exons were sequenced and characterized, mapping up to 29 distinct genes to the mouse cluster, including Il4 and Csf2. Northern blot and RT-PCR analyses indicate that all of these genes are expressed. Analysis of 1 Mb of published sequence from the region of conserved synteny on human chromosome 5q31-q33 identified 45 gene candidates, including 35 expressed genes in the human IL-4 cytokine gene cluster. Probes for 20 human genes were tested for cross-hybridization to murine BAC and PAC clones, thereby mapping 11 additional genes to the mouse complex. Thus, a total of 40 genes including 6 cytokine genes have been physically mapped within 1 Mb of mouse chromosome 11. Gene order in this complex is similar, but not identical, between human and mouse. The integrated physical and transcript maps should prove valuable as a complement to genomic sequencing and expression-dependent transcript maps of this segment of the genome.

KIF2beta, a new kinesin superfamily protein in non-neuronal cells, is associated with lysosomes and may be implicated in their centrifugal translocation

Lysosomes concentrate juxtanuclearly in the region around the microtubule-organizing center by interaction with microtubules. Different experimental and physiological conditions can induce these organelles to move to the cell periphery by a mechanism implying a plus-end-directed microtubule-motor protein (a kinesin-like motor). The responsible kinesin-superfamily protein, however, is unknown. We have identified a new mouse isoform of the kinesin superfamily, KIF2beta, an alternatively spliced isoform of the known, neuronal kinesin, KIF2. Developmental expression pattern and cell-type analysis in vivo and in vitro reveal that KIF2beta is abundant at early developmental stages of the hippocampus but is then downregulated in differentiated neuronal cells, and it is mainly or uniquely expressed in non-neuronal cells while KIF2 remains exclusively neuronal. Electron microscopy of mouse fibroblasts and immunofluorescence of KIF2beta-transiently-transfected fibroblasts show KIF2 and KIF2beta primarily associated with lysosomes, and this association can be disrupted by detergent treatment. In KIF2beta-overexpressing cells, lysosomes (labeled with anti-lysosome-associated membrane protein-1) become abnormally large and peripherally located at some distance from their usual perinuclear positions. Overexpression of KIF2 or KIF2beta does not change the size or distribution of early, late and recycling endosomes nor does overexpression of different kinesin superfamily proteins result in changes in lysosome size or positioning. These results implicate KIF2beta as a motor responsible for the peripheral translocation of lysosomes.

Cloning and characterization of a novel gene (TM7SF1) encoding a putative seven-pass transmembrane protein that is upregulated during kidney development

We have used the cDNA differential display of mRNA technique to isolate genes differentially regulated during kidney development. Here we report the identification of a novel gene, TM7SF1, which is upregulated in the course of kidney development. The full-length cDNA of TM7SF1 is about 2.4 kb and contains an open reading frame of 1197 nucleotides. The predicted secondary structure of the corresponding protein displays seven putative helical transmembrane domains, a structural feature shared by all members of the G-protein-coupled receptor class of transmembrane proteins. Two minor alternatively spliced versions of approximately 2.3 and approximately 2.2 kb could be detected, one of which contains a nearly identical open reading frame with a truncated carboxy-terminus of the deduced protein. The second alternatively spliced version harbors a completely shifted open reading frame with a potential new ATG start codon. By the use of single-chromosome hybrid cells and fluorescence in situ hybridization experiments, TM7SF1 could be localized to chromosome 1q42-q43. Human multiple tissue Northern blot analysis revealed TM7SF1 transcripts in human kidney, heart, brain, and placenta tissue. Studies on Wilms tumor samples showed variable TM7SF1 expression, ranging from nearly undetectable levels to an abundant level of expression comparable to that of adult kidney tissue.