The PITSLRE protein kinase family

Identification and Functional Characterisation of CRK12:CYC9, a Novel Cyclin-Dependent Kinase (CDK)-Cyclin Complex in Trypanosoma brucei

The protozoan parasite, Trypanosoma brucei, is spread by the tsetse fly and causes trypanosomiasis in humans and animals. Both the life cycle and cell cycle of the parasite are complex. Trypanosomes have eleven cdc2-related kinases (CRKs) and ten cyclins, an unusually large number for a single celled organism. To date, relatively little is known about the function of many of the CRKs and cyclins, and only CRK3 has previously been shown to be cyclin-dependent in vivo. Here we report the identification of a previously uncharacterised CRK:cyclin complex between CRK12 and the putative transcriptional cyclin, CYC9. CRK12:CYC9 interact to form an active protein kinase complex in procyclic and bloodstream T. brucei. Both CRK12 and CYC9 are essential for the proliferation of bloodstream trypanosomes in vitro, and we show that CRK12 is also essential for survival of T. brucei in a mouse model, providing genetic validation of CRK12:CYC9 as a novel drug target for trypanosomiasis. Further, functional characterisation of CRK12 and CYC9 using RNA interference reveals roles for these proteins in endocytosis and cytokinesis, respectively.

Analyses of CDC2L1 gene mutations in keloid tissue

BACKGROUND

Keloid disease is the result of a deregulated wound-healing process. Loss of heterozygosity on chromosome 1p36 has been shown to be associated with keloid formation in humans. The cell division cycle 2-like 1 (CDC2L1) gene is known to be essential for eukaryotic cell-cycle control, and has also been mapped to 1p36.

AIM

To verify the possible association between keloid disease and somatic mutation of the CDC2L1 gene on chromosome 1p36.

METHODS

Mutations of the CDC2L1 gene in keloid and healthy skin tissues were screened by denaturing high-performance liquid chromatography, and confirmed by DNA sequencing analysis.

RESULTS

Of the 27 patients with keloid assessed, 21 had mutations. The most prevalent exon affected was exon 7, with 15 patients affected: 10 patients (37%) had a base G deletion at codon 247, and 12 patients (44.4%) had a base A insertion at codon 267 (6 patients (25.9%) had both mutations). The remaining six patients had mutations in exons 11 (codon 433; n = 3) and 14 (codon 520; n = 3). Comparing the keloid skin tissues with the healthy control skin tissues, significant differences were seen between the groups for the base G deletion at codon 247 and the base A insertion at codon 267.

CONCLUSIONS

We have identified a correlation between two exon 7 mutations of the CDC2L1 gene and keloid disease. A further study of protein-kinase activity should be conducted to confirm the functionality of the CDC2L1 gene in the prevention of scar formation.

Translational control of eukaryotic gene expression

Translational control mechanisms are, besides transcriptional control and mRNA stability, the most determining for final protein levels. A large number of accessory factors that assist the ribosome during initiation, elongation, and termination of translation are required for protein synthesis. Cap-dependent translational control occurs mainly during the initiation step, involving eukaryotic initiation factors (eIFs) and accessory proteins. Initiation is affected by various stimuli that influence the phosphorylation status of both eIF4E and eIF2 and through binding of 4E-binding proteins to eIF4E, which finally inhibits cap- dependent translation. Under conditions where cap-dependent translation is hampered, translation of transcripts containing an internal ribosome entry site can still be supported in a cap-independent manner. An interesting example of translational control is the switch between cap-independent and cap-dependent translation during the eukaryotic cell cycle. At the G1-to-S transition, translation occurs predominantly in a cap-dependent manner, while during the G2-to-M transition, cap-dependent translation is inhibited and transcripts are predominantly translated through a cap-independent mechanism.

Par-4 is an essential downstream target of DAP-like kinase (Dlk) in Dlk/Par-4-mediated apoptosis

Prostate apoptosis response-4 (Par-4) was initially identified as a gene product up-regulated in prostate cancer cells undergoing apoptosis. In rat fibroblasts, coexpression of Par-4 and its interaction partner DAP-like kinase (Dlk, which is also known as zipper-interacting protein kinase [ZIPK]) induces relocation of the kinase from the nucleus to the actin filament system, followed by extensive myosin light chain (MLC) phosphorylation and induction of apoptosis. Our analyses show that the synergistic proapoptotic effect of Dlk/Par-4 complexes is abrogated when either Dlk/Par-4 interaction or Dlk kinase activity is impaired. In vitro phosphorylation assays employing Dlk and Par-4 phosphorylation mutants carrying alanine substitutions for residues S154, T155, S220, or S249, respectively, identified T155 as the major Par-4 phosphorylation site of Dlk. Coexpression experiments in REF52.2 cells revealed that phosphorylation of Par-4 at T155 by Dlk was essential for apoptosis induction in vivo. In the presence of the Par-4 T155A mutant Dlk was partially recruited to actin filaments but resided mainly in the nucleus. Consequently, apoptosis was not induced in Dlk/Par-4 T155A-expressing cells. In vivo phosphorylation of Par-4 at T155 was demonstrated with a phospho-specific Par-4 antibody. Our results demonstrate that Dlk-mediated phosphorylation of Par-4 at T155 is a crucial event in Dlk/Par-4-induced apoptosis.

Is the time dimension of the cell cycle re-entry in AD regulated by centromere cohesion dynamics?

Chromosomal involvement is a legitimate, yet not well understood, feature of Alzheimer disease (AD). Firstly, AD affects more women than men. Secondly, the amyloid-β protein precursor genetic mutations, responsible for a cohort of familial AD cases, reside on chromosome 21, the same chromosome responsible for the developmental disorder Down's syndrome. Thirdly, lymphocytes from AD patients display a novel chromosomal phenotype, namely premature centromere separation (PCS). Other documented morphological phenomena associated with AD include the occurrence of micronuclei, aneuploidy, binucleation, telomere instability, and cell cycle re-entry protein expression. Based on these events, here we present a novel hypothesis that the time dimension of cell cycle re-entry in AD is highly regulated by centromere cohesion dynamics. In view of the fact that neurons can re-enter the cell division cycle, our hypothesis predicts that alterations in the signaling pathway leading to premature cell death in neurons is a consequence of altered regulation of the separation of centromeres as a function of time. It is well known that centromeres in the metaphase-anaphase transition separate in a non-random, sequential order. This sequence has been shown to be deregulated in aging cells, various tumors, syndromes of chromosome instability, following certain chemical inductions, as well as in AD. Over time, premature chromosome separation is both a result of, and a driving force behind, further cohesion impairment, activation of cyclin dependent kinases, and mitotic catastrophe, a vicious circle resulting in cellular degeneration and death.

A genome-wide RNA interference screen in Drosophila melanogaster cells for new components of the Hh signaling pathway

Members of the Hedgehog (Hh) family of signaling proteins are powerful regulators of developmental processes in many organisms and have been implicated in many human disease states. Here we report the results of a genome-wide RNA interference screen in Drosophila melanogaster cells for new components of the Hh signaling pathway. The screen identified hundreds of potential new regulators of Hh signaling, including many large protein complexes with pleiotropic effects, such as the coat protein complex I (COPI) complex, the ribosome and the proteasome. We identified the multimeric protein phosphatase 2A (PP2A) and two new kinases, the D. melanogaster orthologs of the vertebrate PITSLRE and cyclin-dependent kinase-9 (CDK9) kinases, as Hh regulators. We also identified a large group of constitutive and alternative splicing factors, two nucleoporins involved in mRNA export and several RNA-regulatory proteins as potent regulators of Hh signal transduction, indicating that splicing regulation and mRNA transport have a previously unrecognized role in Hh signaling. Finally, we showed that several of these genes have conserved roles in mammalian Hh signaling.

The Aspergillus nidulans npkA gene encodes a Cdc2-related kinase that genetically interacts with the UvsBATR kinase

The DNA damage response is a protective mechanism that ensures the maintenance of genomic integrity. We have used Aspergillus nidulans as a model system to characterize the DNA damage response caused by the antitopoisomerase I drug, camptothecin. We report the molecular characterization of a p34Cdc2-related gene, npkA, from A. nidulans. The npkA gene is transcriptionally induced by camptothecin and other DNA-damaging agents, and its induction in the presence of camptothecin is dependent on the uvsBATR gene. There were no growth defects, changes in developmental patterns, increased sensitivity to DNA-damaging agents, or effects on septation or growth rate in the A. nidulans npkA deletion strain. However, the DeltanpkA mutation can partially suppress HU sensitivity caused by the DeltauvsBATR and uvsD153ATRIP checkpoint mutations. We demonstrated that the A. nidulans uvsBATR gene is involved in DNA replication and the intra-S-phase checkpoints and that the DeltanpkA mutation can suppress its intra-S-phase checkpoint deficiency. There is a defect in both the intra-S-phase and DNA replication checkpoints due to the npkA inactivation when DNA replication is slowed at 6 mm HU. Our results suggest that the npkA gene plays a role in cell cycle progression during S-phase as well as in a DNA damage signal transduction pathway in A. nidulans.

Regulation of the cell-cycle-dependent internal ribosome entry site of the PITSLRE protein kinase: roles of Unr (upstream of N-ras) protein and phosphorylated translation initiation factor eIF-2alpha

The PITSLRE kinases belong to the large family of cyclin-dependent protein kinases. Their function has been related to cell-cycle regulation, splicing and apoptosis. We have previously shown that the open reading frame of the p110(PITSLRE) transcript contains an IRES (internal ribosome entry site) that allows the expression of a smaller p58(PITSLRE) isoform during the G2/M stage of the cell cycle. In the present study we investigated further the role of cis- and trans-acting factors in the regulation of the PITSLRE IRES. Progressive deletion analysis showed that both a purine-rich sequence and a Unr (upstream of N-ras) consensus binding site are essential for PITSLRE IRES activity. In line with these observations, we demonstrate that the PITSLRE IRES interacts with the Unr protein, which is more prominently expressed at the G2/M stage of the cell cycle. We also show that phosphorylation of the alpha-subunit of the canonical initiation factor eIF-2 is increased at G2/M. Interestingly, phosphorylation of eIF-2alpha has a permissive effect on the efficiency of both the PITSLRE IRES and the ornithine decarboxylase IRES, two cell cycle-dependent IRESs, in mediating internal initiation of translation, whereas this was not observed with the viral EMCV (encephalomyocarditis virus) and HRV (human rhinovirus) IRESs.

Delineation of mechanisms and regions of dosage imbalance in complex rearrangements of 1p36 leads to a putative gene for regulation of cranial suture closure

Structural chromosome abnormalities have aided in gene identification for over three decades. Delineation of the deletion sizes and rearrangements allows for phenotype/genotype correlations and ultimately assists in gene identification. In this report, we have delineated the precise rearrangements in four subjects with deletions, duplications, and/or triplications of 1p36 and compared the regions of imbalance to two cases recently published. Fluorescence in situ hybridization (FISH) analysis revealed the size, order, and orientation of the duplicated/triplicated segments in each subject. We propose a premeiotic model for the formation of these complex rearrangements in the four newly ascertained subjects, whereby a deleted chromosome 1 undergoes a combination of multiple breakage-fusion-bridge (BFB) cycles and inversions to produce a chromosome arm with a complex rearrangement of deleted, duplicated and triplicated segments. In addition, comparing the six subjects' rearrangements revealed a region of overlap that when triplicated is associated with craniosynostosis and when deleted is associated with large, late-closing anterior fontanels. Within this region are the MMP23A and -B genes. We show MMP23 gene expression at the cranial sutures and we propose that haploinsufficiency results in large, late-closing anterior fontanels and overexpression results in craniosynostosis. These data emphasize the important role of cytogenetics in investigating and uncovering the etiologies of human genetic disease, particularly cytogenetic imbalances that reveal potentially dosage-sensitive genes.

Response of Ewing tumor cells to forced and activated p53 expression

The EWS-FLI1 transcription factor is consistently expressed in 85% of Ewing tumors (EFT). In heterologous cells, EWS-FLI1 induces p53-dependent cell cycle arrest or apoptosis. It has been speculated that the p53 tumor suppressor pathway may be generally compromised in EFT despite only rare p53 mutations. In order to test for functional integrity of this pathway, we have investigated a series of EFT cell lines that differ from each other with respect to their endogenous p53 and INK4A gene status for their response to ectopic p53 expression and to stimulation of endogenous p53 activity by X-ray treatment. Significant interindividual and intratumoral variations in the apoptotic propensity of EFT cell lines to transient expression of ectopic p53 were observed, which was independent of the level of p53 expression. In cell lines with a low apoptotic incidence, apoptosis was delayed and the surviving fraction showed a prolonged growth arrest. Complete resistance to p53-induced apoptosis in two cell lines established from the same patient was associated with a high BCL2/BAX ratio and low levels of APAF1. Sensitivity to X-rays showed a trend towards a higher apoptotic rate in wild-type (wt) p53 expressing than in p53 mutant cells. However, one wt p53-expressing EFT cell line was completely refractory to irradiation-stimulated cell death despite high apoptotic responsiveness to ectopic p53. No difference in Ser15 phosphorylation and the transcriptional activation of p53 targets was observed in wt p53 EFT cell lines irrespective of the induction of cell death or growth arrest. All together, our results demonstrate that despite significant variability in the outcome, cell death or cell cycle arrest, the p53 downstream pathway and the DNA damage signaling pathway are functionally intact in EFT.

L63, the Drosophila PFTAIRE, interacts with two novel proteins unrelated to cyclins

L63 encodes a CDK-like protein homologous to the mammalian PFTAIRE. We showed previously that L63 provides a CDK-related function critical to development (Dev. Biol. 221 (2000) 23). We present here the first biochemical characterization of L63 kinase. In addition, we describe two novel Drosophila proteins, PIF-1 and PIF-2 (for PFTAIRE Interacting Factor-1 and -2), identified in a two-hybrid screen for their ability to interact with the amino-terminal region of L63. The full-length PIF-1 cDNA shows an unusual dicistronic organization. PIF-1A and PIF-1B (the L63 interactor) predicted proteins are expressed in vivo, and show a distinct expression profile during development. Interaction between L63 and PIF-1B was confirmed in vitro and in vivo. The role of this interaction remains to be demonstrated, but our data suggest that PIF-1B might serve as a regulator of L63.

Identification of a novel isoform of Cdk9

Positive transcription factor b (P-TEFb) is required for RNA polymerase II to make the transition from abortive to productive elongation. This important factor is a heterodimer of a cyclin-dependent kinase, cyclin-dependent kinase 9 (Cdk9), and one of four cyclin partners, cyclin T1, T2a, T2b or K. We demonstrate here that there exists in cells a second form of Cdk9 that is 13 kDa larger than the protein originally identified. Both of these forms, which we name Cdk9(42) and Cdk9(55), are present in HeLa and NIH/3T3 cells. Cdk9(55) is generated from an mRNA that originates from a second promoter located upstream of the startpoint of transcription used to generate mRNAs encoding Cdk9(42). Antibodies specific for Cdk9(55) immunoprecipitate Cdk(55) and cyclin T1, but not Cdk9(42). Cdk9(55) in the immunoprecipitates is active as judged by its ability to phosphorylate the carboxyl-terminal domain of the largest subunit of RNA polymerase II. Recently it has been shown that the activity of P-TEFb is negatively regulated in cells by reversible association with a small cellular RNA called 7SK. We show here that P-TEFb molecules containing either form of Cdk9 are found in association with 7SK and both complexes are disrupted by treatment with 600 mM KCl. The relative abundance of Cdk9(55) and Cdk9(42) changes in different cell types, including HeLa, NIH/3T3, human macrophages and mouse lung tissue. Additionally, treatment of macrophages with lipopolysaccharides or infection with human immunodeficiency virus alters the relative abundance of the two forms of Cdk9.

Cyclin-dependent kinase homologues of Plasmodium falciparum

The intraerythrocytic asexual cycle of the malarial parasite is complex and atypical: during schizogony the parasite undergoes multiple rounds of DNA replication and asynchronous nuclear division without cytokinesis. This cell cycle deviates from the classical eukaryotic cell cycle model where, 'DNA replicates only once per cell cycle'. A clear understanding of the molecular switches that control this unusual developmental cycle would be of great interest, both in terms of fundamental Plasmodium biology and in terms of novel potential drug target identification. In recent years considerable effort has been made to identify the malarial orthologues of the cyclin-dependent kinases, which are key regulators of the orderly progression of the eukaryotic cell cycle. This review focuses on the current state-of-knowledge of Plasmodium falciparum cyclin-dependent kinase-like kinases and their regulators.

Regulation of the CDK-related protein kinase PCTAIRE-1 and its possible role in neurite outgrowth in Neuro-2A cells

PCTAIRE-1 is a CDK-related protein kinase found in terminally differentiated cells in brain and testis, and in many immortalised and transformed cell lines. Bacterially expressed PCTAIRE is completely inactive as a protein kinase, but is a very good substrate for protein kinase A (PKA),which phosphorylates a total of four sites in the N-terminus of PCTAIRE-1. Phosphorylation of one of these sites, Ser119, generates a 14-3-3 binding site, which is functional in vitro as well as in vivo. Mutation of another PKA site, Ser153, to an alanine residue generated an activated kinase in transfected mammalian cells. This activity was comparable to that of CDK5 activated by a bacterially expressed, truncated version of p35nck,p21. Gel filtration analysis of a brain extract suggested that monomeric PCTAIRE-1 was the active species, implying that PCTAIRE-1 may not be a true CDK, in that it does not require a partner (cyclin-like) subunit for kinase activity. Finally, we found that various forms of PCTAIRE-1 transfected into neuroblastoma cell lines could either promote or inhibit neurite outgrowth,suggesting a potential role for the PCTAIRE-1 gene product in the control of neurite outgrowth.

Effect of p58GTA on beta-1,4-galactosyltransferase 1 activity and cell-cycle in human hepatocarcinoma cells

Beta-1,4-galactosyltransferase 1 (beta1,4-GT 1) is the key enzyme transferring galactose to the terminal N-acetylglucosamine (GlcNAc) forming Galbeta3-->4GlcNAc structure in the Golgi apparatus. In addition, it also serves as a cell adhesion molecule by recognizing and binding to terminal GlcNAc of glycoconjugates on the adjacent cell surface and matrix through a subpopulation of the enzyme distributed on the cell surface. Transient expression of the p58GTA protein kinase, which belongs to the p34cdc2-related supergene family, could enhance beta1,4-GT 1 total activity in COS cells. In this study, the p58GTA interaction with beta1,4-GT 1 was confirmed using an in vitro assay with the TNT Coupled Reticulocyte Lysate System. An expression vector containing p58GTA was stably transfected into 7721 cells, a human hepatocarcinoma cell line, expression was confirmed by Northern and Western blot analyses. The cells transfected with p58GTA (p58GTA/7721) contained 1.9 times higher total beta1,4-GT 1 activity and 2.6 times higher cell-surface beta1,4-GT 1 activity than the mock transfected cells (pcDNA3/7721). However, Ricinus communis agglutinin-I lectin blot analysis revealed that the enhanced beta1,4-GT1 activity did not increase the Galbetal-->4GlcNAc groups on most of the membrane proteins in p58GTA/7721 cells. By flow cytometry analysis, it was found that the p58GTA/7721 cells were G2/M phase arrested, compared with the pcDNA3/7721 cells. These results suggest that the p58GTA stable transfection into human hepatocarcinoma cells could enhance the two beta1,4-GT1 subcellular pool activities independently and change its cell-cycle without modifying the beta-1,4-linked galactose residues on most membrane proteins.

Update on genetic events in the pathogenesis of melanoma

Melanoma is the most common fatal malignancy among young adults, and its incidence and mortality continue to increase at an alarming rate. Epidemiologic studies have clearly demonstrated roles for genetic predisposition and sun exposure in melanoma development. In the past few years, substantial information has been added to the body of evidence suggesting that inherited and somatic genetic events contribute to the pathogenesis of melanoma. This review focuses on recent advances in the understanding of the genetic events, particularly aberration of cell cycle control and transcriptional control mechanisms, implicated in the pathogenesis of melanoma.

Identification of diverse nerve growth factor-regulated genes by serial analysis of gene expression (SAGE) profiling

Neurotrophic factors such as nerve growth factor (NGF) promote a wide variety of responses in neurons, including differentiation, survival, plasticity, and repair. Such actions often require changes in gene expression. To identify the regulated genes and thereby to more fully understand the NGF mechanism, we carried out serial analysis of gene expression (SAGE) profiling of transcripts derived from rat PC12 cells before and after NGF-promoted neuronal differentiation. Multiple criteria supported the reliability of the profile. Approximately 157,000 SAGE tags were analyzed, representing at least 21,000 unique transcripts. Of these, nearly 800 were regulated by 6-fold or more in response to NGF. Approximately 150 of the regulated transcripts have been matched to named genes, the majority of which were not previously known to be NGF-responsive. Functional categorization of the regulated genes provides insight into the complex, integrated mechanism by which NGF promotes its multiple actions. It is anticipated that as genomic sequence information accrues the data derived here will continue to provide information about neurotrophic factor mechanisms.

Evolution of cyclin-dependent kinases (CDKs) and CDK-activating kinases (CAKs): differential conservation of CAKs in yeast and metazoa

Cyclin-dependent kinases (CDKs) function as central regulators of both the cell cycle and transcription. CDK activation depends on phosphorylation by a CDK-activating kinase (CAK). Different CAKs have been identified in budding yeast, fission yeast, and metazoans. All known CAKs belong to the extended CDK family. The sole budding yeast CAK, CAK1, and one of the two CAKs in fission yeast, csk1, have diverged considerably from other CDKs. Cell cycle regulatory components have been largely conserved in eukaryotes; however, orthologs of neither CAK1 nor csk1 have been identified in other species to date. To determine the evolutionary relationships of yeast and metazoan CAKs, we performed a phylogenetic analysis of the extended CDK family in budding yeast, fission yeast, humans, the fruit fly Drosophila melanogaster, and the nematode Caenorhabditis elegans. We observed that there were 10 clades for CDK-related genes, of which seven appeared ancestral, containing both yeast and metazoan genes. The four clades that contain CDKs that regulate transcription by phosphorylating the carboxyl-terminal domain (CTD) of RNA Polymerase II generally have only a single orthologous gene in each species of yeast and metazoans. In contrast, the ancestral cell cycle CDK (analogous to budding yeast CDC28) gave rise to a number of genes in metazoans, as did the ancestor of budding yeast PHO85. One ancestral clade is unique in that there are fission yeast and metazoan members, but there is no budding yeast ortholog, suggesting that it was lost subsequent to evolutionary divergence. Interestingly, CAK1 and csk1 branch together with high bootstrap support values. We used both the relative apparent synapomorphy analysis (RASA) method in combination with the S-F method of sampling reduced character sets and gamma-corrected distance methods to confirm that the CAK1/csk1 association was not an artifact of long-branch attraction. This result suggests that CAK1 and csk1 are orthologs and that a central aspect of CAK regulation has been conserved in budding and fission yeast. Although there are metazoan CDK-family members for which we could not define ancestral lineage, our analysis failed to identify metazoan CAK1/csk1 orthologs, suggesting that if the CAK1/csk1 gene existed in the metazoan ancestor, it has not been conserved.

Life and death decisions: regulation of apoptosis by proteolysis of signaling molecules

Caspases are the major executioners of cell death, serving as molecular guillotines to behead many proteins required for maintenance of cellular homeostasis. Identification of caspase substrates has taken on increasing importance as we attempt to better understand the molecular mechanisms involved in regulating the struggle between life and death. Many caspase substrates have been described and include RNA binding proteins such as La and U1-70 kD, structural proteins such as keratin and nuclear lamins, and transcription factors or their regulatory proteins that include IkappaB, SP1, and SREBP. Kinases and other signaling proteins are perfectly suited to regulate life and death decisions in response to cellular stressors and have only recently been identified as important caspase substrates. Here we review the current status of signaling pathways that are activated, inactivated or dysregulated by proteases such as caspases and calpain to control entry into apoptosis. The emerging concept that some caspase pathways may be inhibited by cellular and viral apoptosis inhibitory proteins while other caspase pathways are preserved suggests that a subset of these kinases may exist as cleaved 'isoforms' in cells that are not destined to perish. By acting as executioners and as important 'molecular sensors' of the degree of cellular injury, the signaling proteins described in this review are strong candidates to mediate downstream events, both in condemned and in viable cells.

The plant cell cycle in context

Biological scientists are eagerly confronting the challenge of understanding the regulatory mechanisms that control the cell division cycle in eukaryotes. New information will have major implications for the treatment of growth-related diseases and cancer in animals. In plants, cell division has a key role in root and shoot growth as well as in the development of vegetative storage organs and reproductive tissues such as flowers and seeds. Many of the strategies for crop improvement, especially those aimed at increasing yield, involve the manipulation of cell division. This review describes, in some detail, the current status of our understanding of the regulation of cell division in eukaryotes and especially in plants. It also features an outline of some preliminary attempts to exploit transgenesis for manipulation of plant cell division.