Transcripts of one of two Drosophila cyclin genes become localized in pole cells during embryogenesis

Kita-Kyushu Lung Cancer Antigen-1 (KK-LC-1): A Promising Cancer Testis Antigen

Cancer has always been a huge problem in the field of human health, and its early diagnosis and treatment are the key to solving this problem. Cancer testis antigens (CTAs) are a family of multifunctional proteins that are specifically expressed in male spermatozoa and tumor cells but not in healthy somatic cells. Studies have found that CTAs are involved in the occurrence and development of tumors, and some CTAs trigger immunogenicity, which suggests a possibility of tumor immunotherapy. The differential expression and function of CTAs in normal tissues and tumor cells can promote the screening of tumor markers and the development of new immunotherapies. This article introduces the expression of Kita-Kyushu lung cancer antigen-1 (KK-LC-1), a new member of the CTA family, in different types of tumors and its role in immunotherapy.

Oncogenic cancer/testis antigens are a hallmarker of cancer and a sensible target for cancer immunotherapy

Increasing evidence shows that numerous cancer-testis antigens (CTAs) are uniquely overexpressed in various types of cancer and most CTAs are oncogenic. Overexpression of oncogenic CTAs promotes carcinogenesis, cancer metastasis, and drug resistance. Oncogenic CTAs are generally associated with poor prognosis in cancer patients and are an important hallmark of cancer, making them a crucial target for cancer immunotherapy. CTAs-targeted antibodies, vaccines, and chimeric antigen receptor-modified T cells (CAR-T) have recently been used in cancer treatment and achieved promising outcomes in the preclinical and early clinical trials. However, the efficacy of current CTA-targeted therapeutics is either moderate or low in cancer therapy. CTA-targeted cancer immunotherapy is facing enormous challenges. Several critical scientific problems need to be resolved: (1) the antigen presentation function of MHC-I protein is usually deficient in cancer patients, so that very low amounts of intracellular CTA epitopes are presented to tumor cell membrane surface, leading to weak immune response and subsequent immunity to CTAs; (2) various immunosuppressive cells are rich in tumor tissues leading to diminished tumor immunity; (3) the tumor tissue microenvironment markedly reduces the efficacy of cancer immunotherapy. In the current review paper, the authors propose new strategies and approaches to overcome the barriers of CTAs-targeted immunotherapy and to develop novel potent immune therapeutics against cancer. Finally, we highlight that the oncogenic CTAs have high tumor specificity and immunogenicity, and are sensible targets for cancer immunotherapy. We predict that CTAs-targeted immunotherapy will bring about breakthroughs in cancer therapy in the near future.

The Ecdysone receptor constrains wingless expression to pattern cell cycle across the Drosophila wing margin in a Cyclin B-dependent manner

Background

Ecdysone triggers transcriptional changes via the ecdysone receptor (EcR) to coordinate developmental programs of apoptosis, cell cycle and differentiation. Data suggests EcR affects cell cycle gene expression indirectly and here we identify Wingless as an intermediary factor linking EcR to cell cycle.

Results

We demonstrate EcR patterns cell cycle across the presumptive Drosophila wing margin by constraining wg transcription to modulate CycB expression, but not the previously identified Wg-targets dMyc or Stg. Furthermore co-knockdown of Wg restores CycB patterning in EcR knockdown clones. Wg is not a direct target of EcR, rather we demonstrate that repression of Wg by EcR is likely mediated by direct interaction between the EcR-responsive zinc finger transcription factor Crol and the wg promoter.

Conclusions

Thus we elucidate a critical mechanism potentially connecting ecdysone with patterning signals to ensure correct timing of cell cycle exit and differentiation during margin wing development.

Differential roles of HOW in male and female Drosophila germline differentiation

The adult gonads in both male and female Drosophila melanogaster produce gametes that originate from a regenerative pool of germline stem cells (GSCs). The differentiation programme that produces gametes must be co-ordinated with GSC maintenance and proliferation in order to regulate tissue regeneration. The HOW RNA-binding protein has been shown to maintain mitotic progression of male GSCs and their daughters by maintenance of Cyclin B expression as well as suppressing accumulation of the differentiation factor Bam. Loss of HOW function in the male germline results in loss of GSCs due to a delay in G2 and subsequent apoptosis. Here we show that female how mutant GSCs do not have any cell cycle defects although HOW continues to bind bam mRNA and suppress Bam expression. The role of HOW in suppressing germ cell Bam expression appears to be conserved between sexes, leading to different cellular outcomes in how mutants due to the different functions of Bam. In addition the role in maintaining Cyclin B expression has not been conserved so female how GSCs differentiate rather than arrest.

Microarray analysis identifies candidate genes for key roles in coral development

BACKGROUND

Anthozoan cnidarians are amongst the simplest animals at the tissue level of organization, but are surprisingly complex and vertebrate-like in terms of gene repertoire. As major components of tropical reef ecosystems, the stony corals are anthozoans of particular ecological significance. To better understand the molecular bases of both cnidarian development in general and coral-specific processes such as skeletogenesis and symbiont acquisition, microarray analysis was carried out through the period of early development - when skeletogenesis is initiated, and symbionts are first acquired.

RESULTS

Of 5081 unique peptide coding genes, 1084 were differentially expressed (P <or= 0.05) in comparisons between four different stages of coral development, spanning key developmental transitions. Genes of likely relevance to the processes of settlement, metamorphosis, calcification and interaction with symbionts were characterised further and their spatial expression patterns investigated using whole-mount in situ hybridization.

CONCLUSION

This study is the first large-scale investigation of developmental gene expression for any cnidarian, and has provided candidate genes for key roles in many aspects of coral biology, including calcification, metamorphosis and symbiont uptake. One surprising finding is that some of these genes have clear counterparts in higher animals but are not present in the closely-related sea anemone Nematostella. Secondly, coral-specific processes (i.e. traits which distinguish corals from their close relatives) may be analogous to similar processes in distantly related organisms. This first large-scale application of microarray analysis demonstrates the potential of this approach for investigating many aspects of coral biology, including the effects of stress and disease.

APC/CFzr/Cdh1 promotes cell cycle progression during the Drosophila endocycle

The endocycle is a commonly observed variant cell cycle in which cells undergo repeated rounds of DNA replication with no intervening mitosis. How the cell cycle machinery is modified to transform a mitotic cycle into endocycle has long been a matter of interest. In both plants and animals, the transition from the mitotic cycle to the endocycle requires Fzr/Cdh1, a positive regulator of the Anaphase-Promoting Complex/Cyclosome (APC/C). However, because many of its targets are transcriptionally downregulated upon entry into the endocycle, it remains unclear whether the APC/C functions beyond the mitotic/endocycle boundary. Here, we report that APC/C Fzr/Cdh1 activity is required to promote the G/S oscillation of the Drosophila endocycle. We demonstrate that compromising APC/C activity, after cells have entered the endocycle, inhibits DNA replication and results in the accumulation of multiple APC/C targets, including the mitotic cyclins and Geminin. Notably, our data suggest that the activity of APC/C Fzr/Cdh1 during the endocycle is not continuous but is cyclic, as demonstrated by the APC/C-dependent oscillation of the pre-replication complex component Orc1. Taken together, our data suggest a model in which the cyclic activity of APC/C Fzr/Cdh1 during the Drosophila endocycle is driven by the periodic inhibition of Fzr/Cdh1 by Cyclin E/Cdk2. We propose that, as is observed in mitotic cycles, during endocycles, APC/C Fzr/Cdh1 functions to reduce the levels of the mitotic cyclins and Geminin in order to facilitate the relicensing of DNA replication origins and cell cycle progression.

Cyclins and cdc2 kinases in Drosophila: genetic analyses in a higher eukaryote

Cyclin proteins and the kinases with which they associate are encoded by gene families in multicellular eukaryotes. A variety of cyclin/kinase complexes with different functions may exist. We have started a genetic dissection of this complexity in Drosophila. We have done experiments to investigate a potential functional overlap between two kinases (Dmcdc2 and Dmcdc2c) and two cyclins (cyclin A and cyclin B). No functional overlap was observed between the Dmcdc2 and the Dmcdc2c kinases. The phenotype resulting from mutations in Dmcdc2 was not affected by altering the level of Dmcdc2c. Our results concerning cyclin A and cyclin B strongly suggest that these two cyclins have largely overlapping functions. Cell proliferation was observed in the absence of either cyclin A or cyclin B, but not if both cyclins were absent. Cyclin A also has essential functions that cannot be taken over by cyclin B, but these functions appear to be required at defined developmental stages in specific tissues only.

The Drosophila PNG kinase complex regulates the translation of cyclin B

The Drosophila PAN GU (PNG) kinase complex regulates the developmental translation of cyclin B. cyclin B mRNA becomes unmasked during oogenesis independent of PNG activity, but PNG is required for translation from egg activation. We find that although polyadenylation of cyclin B augments translation, it is not essential, and a fully elongated poly(A) is not required for translation to proceed. In fact, changes in poly(A) tail length are not sufficient to account for PNG-mediated control of cyclin B translation and of the early embryonic cell cycles. We present evidence that PNG functions instead as an antagonist of PUMILIO-dependent translational repression. Our data argue that changes in poly(A) tail length are not a universal mechanism governing embryonic cell cycles, and that PNG-mediated derepression of translation is an important alternative mechanism in Drosophila.

Genetic basis of human testicular germ cell cancer: insights from the fruitfly and mouse

The prevalence of tumours of the germ line is increasing in the male population. This complex disease has a complex aetiology. We examine the contribution of genetic mutations to the development of germ line tumours in this review. In particular, we concentrate on fly and mouse experimental systems in order to demonstrate that mutations in some conserved genes cause pathologies typical of certain human germ cell tumours, whereas other mutations elicit phenotypes that are unique to the experimental model. Despite these experimental systems being imperfect, we show that they are useful models of human testicular germ cell tumourigenesis.

Resveratrol-induced G2 arrest through the inhibition of CDK7 and p34CDC2 kinases in colon carcinoma HT29 cells

Resveratrol (3,5,4'-trihydroxystilbene), a phytoalexin found in grapes and other food products, has been shown to have cancer chemopreventive activity. However, the mechanism of the anti-carcinogenic activity is not well understood. Here, we offer a possible explanation of its anti-tumor effect. Based on flow cytometric analysis, resveratrol inhibited the proliferation of HT29 colon cancer cells and resulted in their accumulation in the G(2) phase of the cell cycle. Western blot analysis and kinase assays demonstrated that the perturbation of G(2) phase progression by resveratrol was accompanied by the inactivation of p34(CDC2) protein kinase, and an increase in the tyrosine phosphorylated (inactive) form of p34(CDC2). Kinase assays revealed that the reduction of p34(CDC2) activity by resveratrol was mediated through the inhibition of CDK7 kinase activity, while CDC25A phosphatase activity was not affected. In addition, resveratrol-treated cells were shown to have a low level of CDK7 kinase-Thr(161)-phosphorylated p34(CDC2). These results demonstrated that resveratrol induced cell cycle arrest at the G(2) phase through the inhibition of CDK7 kinase activity, suggesting that its anti-tumor activity might occur through the disruption of cell division at the G(2)/M phase.

Profiling patterned transcripts in Drosophila embryos

Here we describe a high-throughput screen to isolate transcripts with spatially restricted patterns of expression in early embryos. Our approach utilizes robotic automation for rapid analysis of sequence-selected cDNAs in a whole-mount in situ hybridization assay. We determined the spatial distribution of a random collection of 778 different genes from an embryonic cDNA library and show that a significant fraction of these exhibit patterned profiles of expression. In addition, gene ontology studies revealed groups of gene products exhibiting shared expression patterns, providing new insights into the largely overlooked effector molecules that function in development. As described in this paper, automated hybridization to whole-mount embryos in situ proved to be straightforward and provided us with a very powerful method for the global survey of gene expression in early embryos. From the perspective of biological significance, our finding that many spatially restricted transcripts correspond to loci encoding novel transcripts that have not been previously identified in nearly saturating genetic screens for maternal effect and zygotic lethals is particularly notable.

Assembly of the Drosophila germ plasm

The Drosophila melanogaster germ plasm has become the paradigm for understanding both the assembly of a specific cytoplasmic localization during oogenesis and its function. The posterior ooplasm is necessary and sufficient for the induction of germ cells. For its assembly, localization of gurken mRNA and its translation at the posterior pole of early oogenic stages is essential for establishing the posterior pole of the oocyte. Subsequently, oskar mRNA becomes localized to the posterior pole where its translation leads to the assembly of a functional germ plasm. Many gene products are required for producing the posterior polar plasm, but only oskar, tudor, valois, germcell-less and some noncoding RNAs are required for germ cell formation. A key feature of germ cell formation is the precocious segregation of germ cells, which isolates the primordial germ cells from mRNA turnover, new transcription, and continued cell division. nanos is critical for maintaining the transcription quiescent state and it is required to prevent transcription of Sex-lethal in pole cells. In spite of the large body of information about the formation and function of the Drosophila germ plasm, we still do not know what specifically is required to cause the pole cells to be germ cells. A series of unanswered problems is discussed in this chapter.

Calcium/calmodulin-dependent phosphorylation and activation of human Cdc25-C at the G2/M phase transition in HeLa cells

The human tyrosine phosphatase (p54(cdc25-c)) is activated by phosphorylation at mitosis entry. The phosphorylated p54(cdc25-c) in turn activates the p34-cyclin B protein kinase and triggers mitosis. Although the active p34-cyclin B protein kinase can itself phosphorylate and activate p54(cdc25-c), we have investigated the possibility that other kinases may initially trigger the phosphorylation and activation of p54(cdc25-c). We have examined the effects of the calcium/calmodulin-dependent protein kinase (CaM kinase II) on p54(cdc25-c). Our in vitro experiments show that CaM kinase II can phosphorylate p54(cdc25-c) and increase its phosphatase activity by 2.5-3-fold. Treatment of a synchronous population of HeLa cells with KN-93 (a water-soluble inhibitor of CaM kinase II) or the microinjection of AC3-I (a specific peptide inhibitor of CaM kinase II) results in a cell cycle block in G2 phase. In the KN-93-arrested cells, p54(cdc25-c) is not phosphorylated, p34(cdc2) remains tyrosine phosphorylated, and there is no increase in histone H1 kinase activity. Our data suggest that a calcium-calmodulin-dependent step may be involved in the initial activation of p54(cdc25-c).

Drosophila Cyclin B3 is required for female fertility and is dispensable for mitosis like Cyclin B

Cyclin B3 has been conserved during higher eukaryote evolution as evidenced by its identification in chicken, nematodes, and insects. We demonstrate that Cyclin B3 is present in addition to Cyclins A and B in mitotically proliferating cells and not detectable in endoreduplicating tissues of Drosophila embryos. Cyclin B3 is coimmunoprecipitated with Cdk1(Cdc2) but not with Cdk2(Cdc2c). It is degraded abruptly during mitosis like Cyclins A and B. In contrast to these latter cyclins, which accumulate predominantly in the cytoplasm during interphase, Cyclin B3 is a nuclear protein. Genetic analyses indicate functional redundancies. Double and triple mutant analyses demonstrate that Cyclins A, B, and B3 cooperate to regulate mitosis, but surprisingly single mutants reveal that neither Cyclin B3 nor Cyclin B is required for mitosis. However, both are required for female fertility and Cyclin B also for male fertility.

RNA localization in development

Cytoplasmic RNA localization is an evolutionarily ancient mechanism for producing cellular asymmetries. This review considers RNA localization in the context of animal development. Both mRNAs and non-protein-coding RNAs are localized in Drosophila, Xenopus, ascidian, zebrafish, and echinoderm oocytes and embryos, as well as in a variety of developing and differentiated polarized cells from yeast to mammals. Mechanisms used to transport and anchor RNAs in the cytoplasm include vectorial transport out of the nucleus, directed cytoplasmic transport in association with the cytoskeleton, and local entrapment at particular cytoplasmic sites. The majority of localized RNAs are targeted to particular cytoplasmic regions by cis-acting RNA elements; in mRNAs these are almost always in the 3'-untranslated region (UTR). A variety of trans-acting factors--many of them RNA-binding proteins--function in localization. Developmental functions of RNA localization have been defined in Xenopus, Drosophila, and Saccharomyces cerevisiae. In Drosophila, localized RNAs program the antero-posterior and dorso-ventral axes of the oocyte and embryo. In Xenopus, localized RNAs may function in mesoderm induction as well as in dorso-ventral axis specification. Localized RNAs also program asymmetric cell fates during Drosophila neurogenesis and yeast budding.

Nanos and Pumilio have critical roles in the development and function of Drosophila germline stem cells

The zinc-finger protein Nanos and the RNA-binding protein Pumilio act together to repress the translation of maternal hunchback RNA in the posterior of the Drosophila embryo, thereby allowing abdomen formation. nanos RNA is localized to the posterior pole during oogenesis and the posteriorly synthesized Nanos protein is sequestered into the germ cells as they form in the embryo. This maternally provided Nanos protein is present in germ cells throughout embryogenesis. Here we show that maternally deposited Nanos protein is essential for germ cell migration. Lack of zygotic activity of nanos and pumilio has a dramatic effect on germline development of homozygous females. Given the coordinate function of nanos and pumilio in embryonic patterning, we analyzed the role of these genes in oogenesis. We find that both genes act in the germline. Although the nanos and pumilio ovarian phenotypes have similarities and both genes ultimately affect germline stem cell development, the focus of these phenotypes appears to be different. While pumilio mutant ovaries fail to maintain stem cells and all germline cells differentiate into egg chambers, the focus of nanos function seems to lie in the differentiation of the stem cell progeny, the cystoblast. Consistent with the model that nanos and pumilio have different phenotypic foci during oogenesis, we detect high levels of Pumilio protein in the germline stem cells and high levels of Nanos in the dividing cystoblasts. We therefore suggest that, in contrast to embryonic patterning, Nanos and Pumilio may interact with different partners in the germline.

Germ plasm in Caenorhabditis elegans, Drosophila and Xenopus

Special cytoplasm, called germ plasm, that is essential for the differentiation of germ cells is localized in a particular region of Caenorhabditis elegans, Drosophila and Xenopus eggs. The mode of founder cell formation of germline, the origin and behavior of the germline granules, and the molecules localized in germline cells are compared in these organisms. The common characteristics of the organisms are mainly as follows. First, the founder cells of germline are established before the initiation of gastrulation. Second, the germline granules or their derivatives are always present in germline cells or germ cells throughout the life cycle in embryos, larvae, and adults. Lastly, among the proteins localized in the germ plasm, only Vasa protein or its homolog is detected in the germline cells or germ cells throughout the life cycle. As the protein of vasa homolog has been reported to be also localized in the germline-specific structure or nuage in some of the organisms without the germ plasm, the possibility that the mechanism for differentiation of primordial germ cells is basically common in all organisms with or without the germ plasm is discussed.

Mutation of a gene for a Drosophila kinesin-like protein, Klp38B, leads to failure of cytokinesis

Mutations in a gene (Klp38B) encoding a novel kinesin-like protein in Drosophila melanogaster lead to the formation of polyploid cells in the larval central nervous system and in the follicle cells of adult egg chambers. Some homozygous mutants survive to adulthood and also exhibit morphological defects indicative of abnormal cell cycle progression, including rough eyes, missing bristles, and abnormal abdominal cuticles. In larval brains, there is no accumulation of mitotic cells and the frequency of anaphase figures is comparable to wild type, suggesting that nuclear division is not affected. Such brains contain polyploid cells with metaphase and anaphase chromosomes associated with bipolar spindles. Such spindles have a number of unseparated centrosomes at their poles reflecting the degree of polyploidy of the cell. Follicle cells frequently contain two nuclei of roughly equal size. Taken together, we conclude that these Klp38B mutations lead to a failure of cytokinesis resulting in polyploidy, and discuss whether or not this is a direct effect of the mutation.

Chromatid segregation at anaphase requires the barren product, a novel chromosome-associated protein that interacts with Topoisomerase II

We have isolated a Drosophila gene, barren (barr), required for sister-chromatid segregation in mitosis. barr encodes a novel protein that is present in proliferating cells and has homologs in yeast and human. Mitotic defects in barr embryos become apparent during cycle 16, resulting in a loss of PNS and CNS neurons. Centromeres move apart at the metaphase-anaphase transition and Cyclin B is degraded, but sister chromatids remain connected, resulting in chromatin bridging. This phenotype is similar to that described in TOP2 mutants in yeast. Barren protein localizes to chromatin throughout mitosis. Colocalization and biochemical experiments indicate that Barren associates with Topoisomerase II throughout mitosis and alters the activity of Topoisomerase II. We propose that this association is required for proper chromosomal segregation by facilitating the decatenation of chromatids at anaphase.

Multiple potential germ-line helicases are components of the germ-line-specific P granules of Caenorhabditis elegans

Two components of the germ-line-specific P granules of the nematode Caenorhabditis elgans have been identified using polyclonal antibodies specific for each. Both components are putative germ-line RNA helicases (GLHs) that contain CCHC zinc fingers of the type found in the RNA-binding nucleocapsid proteins of retroviruses. The predicted GLH-1 protein has four CCHC fingers; GLH-2 has six. Both GLH proteins localize in the P granules at all stage of germ-line development. However, the two glh genes display different patterns of RNA and protein accumulation in the germ lines of hermaphrodites and males. Injection of antisense glh-1 or glh-2 RNA into wild-type worms causes some offspring to develop into sterile adults, suggesting that either or both genes are required for normal germ-line development. As these very similar glh genes physically map within several hundred kilobases of one another, it seems likely that they represent a fairly recent gene duplication event.

WEE1-like CDK tyrosine kinase mRNA level is regulated temporally and spatially in sea urchin embryos

A cDNA from the sea urchin Strongylocentrotus purpuratus encodes a 624 amino acid polypeptide (WEE1S.purp) with a high degree of similarity to the Mik1 and Wee1 protein tyrosine kinases. These kinases act as negative regulators of mitosis by inactivating cyclin-dependent kinases (CDK). Wee1 activity varies during the cell-cycle, and is generated only when required. The pattern of WEE1S.purp mRNA expression was examined temporally and spatially in sea urchin embryos. Only a trace amount of WEE1S.purp mRNA is present in the egg and through the fifth cell cycle post-fertilization. During the next three cycles to the mid-blastula stage, its concentration rises transiently to 2.5 x 10(4) transcripts per embryo. Its developmental profile during this early period is the inverse of that reported for cyclin mRNAs, which are at a high level in the egg and through the fifth cell cycle, then decline upon further development. WEE1S.purp mRNA in the gastrula and pluteus stages becomes restricted to cells engaged in DNA replication, including the endoderm (gut), oral ectoderm, and arm rudiments. It is absent from the aboral ectoderm, which lacks cycling cells. In the pluteus larva of the species Lytechinus pictus, WEE1 mRNA was detected in the arm rudiments during cellular proliferation and arm elongation, but not after the completion of the arms. Putative regulatory motifs in the sea urchin Wee1-like cDNA suggest a capacity for rapid turnover of both its mRNA and protein: The WEE1S.purp mRNA 3' UTR contains 13 AUUUA pentamers, which have been characterized as determinants of mRNA lability; and the N-terminal domain of the predicted WEE1S.purp polypeptide is enriched in S/TP-containing, potential kinase-target sites, as well as high-value "PEST' sequences, associated with protein lability. The developmental appearance of WEE1S.purp mRNA may coincide with the introduction of a gap phase in the cell cycle. Its spatial pattern during embryogenesis appears to reflect distinct programs of regulated cell cycling in differentiating tissues.

Presence and expression of G2 cyclins in the coelenterate hydra

In hydra all cell-cycle control occurs in the G2/M transition. Cyclins acting at this restriction point in the cell cycle belong to the cyclin A and B families. In agreement with this we isolated cDNAs coding for a cyclin A and a cyclin B from the multiheaded mutant of Chlorohydra viridissima and a cyclin B from Hydra vulgaris. The two B-type cyclins from hydra show 85.6% identity at the amino acid level, and 84.8% at the nucleotide level. The relatedness is less extensive than that found for mammals, e.g. human and mouse, and is evidence that the two hydra species diverged early in evolution. From each hydra species only one B-type cyclin was found, showing equal relatedness to the B1 and B2 subtypes of cyclins, hinting at a role as common ancestor before the split into B1 and B2 cyclins occurred. All three hydra cyclins contain regulation signals typical for G2/M cyclins, such as a ubiquitin destruction box at the amino terminus, needed for rapid degradation of the protein, and translation and polyadenylation elements in the 3′ untranslated region to regulate RNA storage and RNA degradation. In hydra cell-cycle times vary depending on feeding regime and growth conditions. Cyclin B RNA expression was found to precede the daily mitotic rhythm induced by feeding. During head regeneration cyclin B expression showed the expected drop early during regeneration and an increase later. At the cellular level strongest expression of cyclin B RNA and protein was detected in interstitial cells which possess with one day the shortest cell-cycle time in hydra. Epithelial cells with a three-day cell-cycle rhythm showed variable, and differentiated cells no cyclin B expression. Regions of hydra containing high numbers of proliferating cells, such as developing buds exhibited elevated levels of cyclin B expression.

Isolation of Drosophila cyclin D, a protein expressed in the morphogenetic furrow before entry into S phase

During Drosophila development, nuclear and cell divisions are coordinated in response to developmental signals. In yeast and mammalian cells, signals that control cell division regulate the activity of cyclin-dependent kinases (Cdks) through proteins such as cyclins that interact with the Cdks. Here we describe two Drosophila cyclins identified from a set of Cdk-interacting proteins. One, cyclin J, is of a distinctive sequence type; its exclusive maternal expression pattern suggests that it may regulate oogenesis or the early nuclear divisions of embryogenesis. The other belongs to the D class of cyclins, previously identified in mammalian cells. We show that Drosophila cyclin D is expressed in early embryos and in imaginal disc cells in a pattern that anticipates cell divisions. Expression in the developing eye disc at the anterior edge of the morphogenetic furrow suggests that cyclin D acts early, prior to cyclin E, in inducing G1-arrested cells to enter S phase. Our results also suggest that, although cyclin D may be necessary, its expression alone is not sufficient to initiate the events leading to S phase.

A Cdc2 dependent checkpoint maintains diploidy in Drosophila

DNA replication in G2 does not normally occur due to the checkpoint control. To elucidate its mechanism, the functions of the escargot and Dmcdc2 genes of Drosophila were studied. When escargot function was eliminated, diploid imaginal cells that were arrested in G2 lost Cyclin A, a regulatory subunit of G2/M cdk, and entered an endocycle. escargot genetically interacted with Dmcdc2 which encodes a catalytic subunit of G2/M cdk. The mutant phenotypes of Dmcdc2 itself was similar to those of escargot: many diploid cells in imaginal discs, salivary glands and the central nervous system entered an endocycle and sometimes formed polytene chromosomes. Since mitotically quiescent abdominal histoblasts still required Dmcdc2 to remain diploid, the inhibitory activity of G2/M cdk on DNA replication appeared to be separable from its activity as the mitosis promoting factor. These results suggest that in G2, escargot is required to maintain a high level of G2/M cdk that actively inhibits the entry into S phase.

Cyclins and cyclin-dependent kinases: a biochemical view

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Drosophila development pulls the strings of the cell cycle

The three cycles of cell division immediately following the formation of the cellular blastoderm during Drosophila embryogenesis display an invariant pattern. Bursts of transcription of a gene called string are required and sufficient to trigger mitosis at this time during development. The activator of mitosis encoded by the string gene is a positive regulator of cdc2 kinase and a Drosophila homologue of the Saccharomyces pombe cdc25 tyrosine phosphatase. Evidence presented in a recent paper demonstrates that transcription of string, and hence the timing and pattern of mitosis in the postblastoderm embryo, is under complex developmental control. Several lines of evidence support this interpretation, including the analysis of string transcription in pattern formation mutants, cell cycle arrest mutants, and the preliminary characterization of an extensive cis-acting regulatory region.

Caenorhabditis elegans cyclin A- and B-type genes: a cyclin A multigene family, an ancestral cyclin B3 and differential germline expression

We have cloned cDNAs for Caenorhabditis elegans cyclins A1, B and B3. While cyclins A1 and B are most closely related to either A- or B-type cyclins of other species, cyclin B3 is less related to these cyclins. However, this cyclin is most similar to the recently identified chicken cyclin B3. Our identification of a Caenorhabditis homolog demonstrates that cyclin B3 has been conserved in evolution. Cyclin A1 is a member of an A-type multigene family; however the cyclin A1 cDNA only recognizes a single band on northern blots. A single-sized RNA is also observed for the cyclin B3 cDNA. In contrast, three different transcripts are observed for the cyclin B cDNA. Based on our analyses using RNAs from germline-defective mutants and from populations enriched for males, one cyclin B transcript is specific to the paternal germline. The two other cyclin B transcripts, as well as the cyclin A1 and cyclin B3 transcripts, are most abundant in the maternal germline and are only present at low levels in other tissues. Moreover, the 3′ untranslated regions of each Caenorhabditis cyclin cDNA possess several copies of potential translational control elements shown in Xenopus and Drosophila maternal cyclin mRNAs to function during oogenesis and early embryogenesis.

Localization and quantification of cyclin A and B mRNA during the embryonic development of Patella vulgata

As the first five cleavages of the Patella vulgata embryo are synchronous, they are well suited to determine the mRNA level of cyclin A and B genes in an embryo. During the third and fourth cleavage cycle the quantity of A and B mRNA is regulated in a cell-cycle-dependent way, reaching a high level between cleavages and a lower level just after mitosis. This implies that transcription of the cyclin genes occurs before the overall transcription increases directly after the fifth cleavage. During the first cleavages cyclin A and B mRNA is localized in distinct parts of the cytoplasm. Between two successive cell devisions it is found as a crescent-shaped domain at the peripheral side of the nucleus. At cytokinesis it is present between two separating nuclei and at newly formed cell membranes. At the fifth cleavage this localization disappears. Changes in the expression pattern of cyclin A and B may be expected after the fifth cleavage, when the first cells become arrested in cell division and differentiate. The mechanism causing cell division arrest of these primary trochoblasts is still unknown. Cell division arrest caused by the absence of cyclin A and/or B mRNA could be conditional for further differentiation. However, a decrease in cyclin A and B mRNA level in the trochoblasts is not detectable until 4 h after their last division. Later in development no cyclin A and B mRNA can be detected in these cells, whereas cyclin A and B mRNA is present in other cells of the embryo. Thus, the absence of cyclin A and B mRNA in primary trochoblasts, and in the later differentiating secondary and accessory trochoblasts is not obligatory for cell division arrest or cell differentiation.

Effects of monocerin on cell cycle progression in maize root meristems synchronized with aphidicolin

Monocerin is a benzopyran fungal toxin with broad activity on plants, fungi and insects. Its effect upon cell cycle progression has been analyzed in maize roots. Meristematic cells were synchronized by treatment with aphidicolin. Flow cytometric DNA analysis and mitotic indices indicated durations of 1.5 h, 5 h, 2 h and 1 h for respectively G1, S, G2 and M phases of the normal cell cycle at 25°C. Treatment of these synchronized meristems with 0.5 mM monocerin during release after an aphidicolin block produced a short delay in S phase and then a more important delay (about 2.5 h) in entry into mitosis. Treatments for similar durations (3 h) during progression through the cycle revealed two periods of action of monocerin. The first appears to be mid to late S and the second one G2, before the transition point between G2 and M. Action on either one of these target periods could lead to a delay in the G2/M transition, but these two responses did not appear to be additive.

Germ cell-less encodes a cell type-specific nuclear pore-associated protein and functions early in the germ-cell specification pathway of Drosophila

The maternally supplied plasm at the posterior pole of a Drosophila embryo contains determinants that specify both the germ-cell precursors (pole cells) and the posterior axis. One pole plasma component, the product of the germ cell-less gene, has been found to be required for specification of pole cells, but not posterior somatic cells. Mothers with reduced levels of gcl give rise to progeny that lack pole cells, but are otherwise normal. Mothers overexpressing gcl, on the other hand, produce progeny exhibiting a transient increase of pole cells. Ectopic localization of gcl to the anterior pole of the embryo causes nuclei at that location to adopt characteristics of pole cell nuclei, with concurrent loss of somatic cells. We also present evidence indicating that the gcl protein associates specifically with the nuclear pores of the pole cell nuclei. This localization suggests a novel mechanism in the specification of cell fate for the germ line.

Genetics of nanos localization in Drosophila

The Drosophila gene nanos is required for two processes. During oogenesis, nanos function is required for the continued production of egg chambers, and nanos is expressed in the early germarium. During embryogenesis, nanos is required maternally to specify abdominal segmentation. Nanos shares this latter function with nine other genes, collectively known as the posterior group. Of this group, nanos encodes a determinant, and is localized as an RNA to the posterior pole of early embryos. This RNA is translated to form a gradient of nanos protein with highest concentrations at the posterior. Analysis of the distribution of nanos gene products in embryos mutant for posterior group genes shows that eight of these genes are required for localization, but not stability, of the nanos RNA. Embryos mutant for posterior group alleles which produce weak abdominal phenotypes show reduced amounts of localized nanos RNA. This correlation between nanos RNA localization and abdominal phenotype suggests that nanos acts as a localization-dependent posterior determinant. Localization of nanos is not affected by mutations in bicoid or torso, confirming that the three maternal systems of anterior-posterior determination initially act independently.

Germ-line determination in Caenorhabditis and Ascaris: Will a helicase begin to unravel the mystery?

How cell lineages are established during development in higher eukaryotes is being addressed by geneticists and by developmental and molecular biologists. In Drosophila melanogaster, a gene corresponding to a germ-line-specific RNA helicase, vasa, has been shown to be a component o f the posteriorly localized germ granules o f the developing embryo. A putative RNA helicase, glh-I r which appears germ-line specific in its expression, has recently been reported from the free-living nematode Caenorhabditis elegans. Parasitologists studying the nematode Ascaris lumbricoides var. suum have found it to be a useful complement to Caenorhabditis. Deborah Roussell, Michael Gruidl and Karen Bennett predict that Ascaris will be valuable in determining the role played by germ-line helicases in development.

Multiple RNA regulatory elements mediate distinct steps in localization of oskar mRNA

Pattern formation in the early development of many organisms relies on localized cytoplasmic proteins, which can be prelocalized as mRNAs. The Drosophila oskar gene, required both for posterior body patterning and germ cell determination, encodes one such mRNA. Localization of oskar mRNA is an elaborate process involving movement of the transcript first into the oocyte from adjacent interconnected nurse cells and then across the length of the oocyte to its posterior pole. We have mapped RNA regulatory elements that direct this localization. Using a hybrid lacZ/oskar mRNA, we identify several elements within the oskar 3′ untranslated region that affect different steps in the process: the early movement into the oocyte, accumulation at the anterior margin of the oocyte and finally localization to the posterior pole. This use of multiple cis-acting elements suggests that localization may be orchestrated in a combinatorial fashion, thereby allowing localized mRNAs with ultimately different destinations to employ common mechanisms for shared intermediate steps.

Mutations in the Drosophila melanogaster gene three rows permit aspects of mitosis to continue in the absence of chromatid segregation

We have cloned the three rows (thr) gene, by a combination of chromosome microdissection and P element tagging. We describe phenotypes of embryos homozygous for mutations at the thr locus. Maternal mRNA and protein appear to be sufficient to allow 14 rounds of mitosis in embryos homozygous for thr mutations. However, a small percentage of cells in syncytial blastoderm stage thr embryos sink into the interior of the embryo as if they have failed to divide properly. Following cellularisation all cells complete mitosis 14 normally. All cells become delayed at mitosis 15 with their chromosomes remaining aligned on the spindle in a metaphase-like configuration, even though both cyclins A and B have both been degraded. As cyclin B degradation occurs at the metaphase-anaphase transition, subsequent to the microtubule integrity checkpoint, the delay induced by mutations at the thr locus defines a later point in mitotic progression. Chromosomes in the cells of thr embryos do not undertake anaphase separation, but remain at the metaphase plate. Subsequently they decondense. A subset of nuclei go on to replicate their DNA but there is no further mitotic division.

A molecular screen for polar-localised maternal RNAs in the early embryo of Drosophila

Localised, maternally synthesised RNAs and proteins play an important role in an early animal embryogenesis. In Drosophila, genetic screens have recovered a number of maternal effect loci that encode localised products in the embryo. However, only a third of Drosophila's genes have been genetically mutated. Consequently, we conducted a molecular screen for polar-localised RNAs in the early Drosophila embryo in order to identify additional maternal molecules that carry out spatially restricted functions during early embryogenesis. Total RNA was purified from anterior or posterior poles cut off early Drosophila embryos. These RNAs were used to construct directionally cloned anterior and posterior cDNA libraries which were used in a differential screen for cDNAs representing maternal RNAs localised to one or other pole of the embryo. Five such clones were identified, representing cyclin B RNA, Hsp83 RNA, 28S ribosomal RNA, mitochondrial cytochrome c oxidase subunit one RNA and mitochondrial 16S large ribosomal RNA. Mutations in the loci encoding these RNAs have not been recovered in genetic screens, confirming that our molecular approach complements genetic strategies for identifying maternal molecules that carry out spatially restricted functions in the early embryo. We consider the possible biological significance of localisation of each of these species of transcripts as well as the mechanism of their localisation, and discuss the potential use of our cDNA libraries in screens for rarer localised RNAs.

Differential function and expression of Saccharomyces cerevisiae B-type cyclins in mitosis and meiosis

We have studied the patterns of expression of four B-type cyclins (Clbs), Clb1, Clb2, Clb3, and Clb4, and their ability to activate p34cdc28 during the mitotic and meiotic cell cycles of Saccharomyces cerevisiae. During the mitotic cell cycle, Clb3 and Clb4 were expressed and induced a kinase activity in association with p34cdc28 from early S phase up to mitosis. On the other hand, Clb1 and Clb2 were expressed and activated p34cdc28 later in the mitotic cell cycle, starting in late S phase and continuing up to mitosis. The pattern of expression of Clb3 and Clb4 suggests a possible role in the regulation of DNA replication as well as mitosis. Clb1 and Clb2, whose pattern of expression is similar to that of other known Clbs, are likely to have a role predominantly in the regulation of M phase. During the meiotic cell cycle, Clb1, Clb3, and Clb4 were expressed and induced a p34cdc28-associated kinase activity just before the first meiotic division. The fact that Clb3 and Clb4 were not synthesized earlier, in S phase, suggests that these cyclins, which probably have a role in S phase during the mitotic cell cycle, are not implicated in premeiotic S phase. Clb2, the primary mitotic cyclin in S. cerevisiae, was not detectable during meiosis. Sporulation experiments on strains deleted for one, two, or three Clbs indicate, in agreement with the biochemical data, that Clb1 is the primary cyclin for the regulation of meiosis, while Clb2 is not involved at all.

Differential function and expression of Saccharomyces cerevisiae B-type cyclins in mitosis and meiosis

We have studied the patterns of expression of four B-type cyclins (Clbs), Clb1, Clb2, Clb3, and Clb4, and their ability to activate p34cdc28 during the mitotic and meiotic cell cycles of Saccharomyces cerevisiae. During the mitotic cell cycle, Clb3 and Clb4 were expressed and induced a kinase activity in association with p34cdc28 from early S phase up to mitosis. On the other hand, Clb1 and Clb2 were expressed and activated p34cdc28 later in the mitotic cell cycle, starting in late S phase and continuing up to mitosis. The pattern of expression of Clb3 and Clb4 suggests a possible role in the regulation of DNA replication as well as mitosis. Clb1 and Clb2, whose pattern of expression is similar to that of other known Clbs, are likely to have a role predominantly in the regulation of M phase. During the meiotic cell cycle, Clb1, Clb3, and Clb4 were expressed and induced a p34cdc28-associated kinase activity just before the first meiotic division. The fact that Clb3 and Clb4 were not synthesized earlier, in S phase, suggests that these cyclins, which probably have a role in S phase during the mitotic cell cycle, are not implicated in premeiotic S phase. Clb2, the primary mitotic cyclin in S. cerevisiae, was not detectable during meiosis. Sporulation experiments on strains deleted for one, two, or three Clbs indicate, in agreement with the biochemical data, that Clb1 is the primary cyclin for the regulation of meiosis, while Clb2 is not involved at all.

Genetic analysis of the Drosophila cdc2 homolog

We have identified mutations in the Drosophila cdc2 gene. The recessive lethality of these mutant alleles was rescued after P-element-mediated transformation with a genomic cdc2 fragment. Sequence analysis of amorphic alleles revealed non-conservative exchanges in evolutionary conserved positions. These alleles caused lethality at the larval-pupal interphase due to the absence of imaginal tissues. Embryonic lethality resulted when the maternal Dm cdc2 contribution was reduced through the use of a temperature-sensitive allele. Dm cdc2 function, therefore, is essential for cell proliferation throughout development. Dm cdc2 function is clearly required for mitosis, but no evidence for a requirement in S-phase was obtained. The reversible block of the mitotic proliferation which was observed in the PNS of mutant embryos occurred exclusively in the G2-phase. Moreover, while the mitotic proliferation of imaginal cells was blocked in the amorphic mutant larvae, non-imaginal larval cells continued to grow and endoreplicate their DNA. The Dm cdc2 mutant phenotype could neither be rescued with Dm cdc2c (encoding a cdc2-like kinase) nor enhanced by a reduction of the Dm cdc2c gene dose. These results indicate that the Dm cdc2- and Dm cdc2c-kinases control different processes.

A 69-kDa RNA-binding protein from Xenopus oocytes recognizes a common motif in two vegetally localized maternal mRNAs

Vg1 mRNA, a maternal message encoding a member of the transforming growth factor beta superfamily, undergoes localization to the vegetal cortex of Xenopus laevis oocytes during a narrow period of oogenesis. A 340-nucleotide sequence has been identified in Vg1 RNA that directs its vegetal localization [Mowry, K. L. & Melton, D. A. (1992) Science 255, 991-994]. To understand how cis- and trans-acting factors are involved in Vg1 mRNA localization, we have looked for specific interactions in vitro between oocyte proteins and Vg1 mRNA. S100 extracts of late-stage oocytes contain a protein-binding activity that protects specific regions of labeled Vg1 mRNA from degradation by RNase T1. The use of different regions of Vg1 RNA in competition reactions reveals two binding sites, both in the first half of the 3' untranslated region of Vg1 message. UV crosslinking predominantly labels a 69-kDa protein; saturation analysis and competitor studies indicate that this protein binds with a high affinity to the down-stream site, which corresponds to the 340-nucleotide vegetal localization sequence. Binding to this region is inhibited by another vegetally localized message, transforming growth factor beta 5 but is not inhibited by an animally localized RNA, An2. These data indicate that vegetally localized mRNAs share a binding motif that helps them achieve their intracellular distribution through specific RNA-protein interactions.

The pebble gene is required for cytokinesis in Drosophila

Cytokinesis is developmentally controlled during Drosophila embryogenesis. It is omitted during the initial nuclear division cycles. The nuclei of the resulting syncytium are then cellularized at a defined stage, and cytokinesis starts in somatic cells with mitosis 14. However, cytokinesis never occurs in somatic cells of embryos homozygous or transheterozygous for mutations in the pebble gene. Interestingly, the process of cellularization, which involves steps mechanistically similar to cytokinesis, is not affected. Moreover, all the nuclear aspects of mitosis (nuclear envelope breakdown, chromosome condensation, spindle assembly and function) proceed normally in pebble mutant embryos, indicating that pebble is specifically required for the coordination of mitotic spindle and contractile ring functions. The pebble phenotype is also observed, but only with very low penetrance, during the early divisions of the germ line progenitors (the pole cells). alpha-Amanitin injection experiments indicate that these early pole cell divisions, the first cell divisions during embryogenesis, do not require zygotic gene expression. These divisions might therefore rely on maternally contributed pebble function. The maternal contribution from heterozygous mothers might be insufficient in rare cases for all the pole cell divisions.

Cleavage and gastrulation in the shrimp Sicyonia ingentis: invagination is accompanied by oriented cell division

Embryos of the penaeoidean shrimp Sicyonia ingentis were examined at intervals during cleavage and gastrulation using antibodies to beta-tubulin and DNA and laser scanning confocal microscopy. Cleavage occurred in a regular pattern within four domains corresponding to the 4-cell-stage blastomeres and resulted in two interlocking bands of cells, each with similar spindle orientations, around a central blastocoel. Right-left asymmetry was evident at the 32-cell-stage, and mirror-image embryos occurred in a 50:50 ratio. Gastrulation was initiated by invagination into the blastocoel at the 62-cell-stage of two mesendoderm cells, which arrested at the 32-cell-stage. Further invagination and expansion of the archenteron during gastrulation was accompanied by rapid and oriented cell division. The archenteron was composed of presumptive naupliar mesoderm and the blastopore was located at the site of the future anus of the nauplius larva. In order to trace cell lineages and determine axial relationships, single 2- and 4-cell-stage blastomeres were microinjected with rhodamine-dextran. The results showed that the mesendoderm cells which initiated gastrulation were derived from the vegetal 2-cell-stage blastomere, which could be distinguished by its slightly larger size and the location of the polar bodies. The mesendoderm cells descended from a single vegetal blastomere of the 4-cell-stage. This investigation provides the first evidence for oriented cell division during gastrulation in a simple invertebrate system. Oriented cell division has previously been discounted as a potential morphogenetic force, and may be a common mechanism of invagination in embryos that begin gastrulation with a relatively small number of cells.

Molecular movements in oocyte patterning and pole cell differentiation

Central to the differentiation and patterning of the Drosophila oocyte is the asymmetric intracellular localization of numerous mRNA and protein molecules involved in developmental signalling. Recent advances have identified some of the molecules mediating oocyte differentiation, specification of the anterior pole of the embryo, and determination of the embryonic germ line. This work is considered in the context of the classical model of the germ plasm as a cytoplasmic determinant for germ cell formation.

The 3' untranslated region of localized maternal messages contains a conserved motif involved in mRNA localization

Messenger RNA (mRNA) localization is emerging as a means of regulating gene expression. This process is operational in fly and frog development, where a subset of maternally inherited RNAs are asymmetrically distributed and thought to impart axial polarity to the embryo. Since most maternal mRNAs are uniformly distributed, an apparatus must exist to recognize and specifically transport these rare localized species. Here I report the identification of a nine-nucleotide motif, YUGUUYCUG, common to the 3' untranslated regions of four sequenced messages of this class: Drosophila bicoid and nanos mRNAs and Xenopus An2 and Vg1 mRNAs. To test the role of this nonamer sequence in the localization process, a Drosophila transient assay has been established. The assay reveals that bicoid mRNA specifically lacking this nonamer is partially mislocalized. In contrast, nonamer deletion is inconsequential to message stability. The existence of specific and general mRNA localization signals is proposed and it is suggested that this conserved motif belongs to the latter category.

Cyclins A and B associate with chromatin and the polar regions of spindles, respectively, and do not undergo complete degradation at anaphase in syncytial Drosophila embryos

Maternally contributed cyclin A and B proteins are initially distributed uniformly throughout the syncytial Drosophila embryo. As dividing nuclei migrate to the cortex of the embryo, the A and B cyclins become concentrated in surface layers extending to depths of approximately 30-40 microns and 5-10 microns, respectively. The initiation of nuclear envelope breakdown, spindle formation, and the initial congression of the centromeric regions of the chromosomes onto the metaphase plate all take place within the surface layer occupied by cyclin B on the apical side of the blastoderm nuclei. Cyclin B is seen mainly, but not exclusively, in the vicinity of microtubules throughout the mitotic cycle. It is most conspicuous around the centrosomes. Cyclin A is present at its highest concentrations throughout the cytoplasm during the interphase periods of the blastoderm cycles, although weak punctate staining can also be detected in the nucleus. It associates with the condensing chromosomes during prophase, segregates into daughter nuclei in association with chromosomes during anaphase, to redistribute into the cytoplasm after telophase. In contrast to the cycles following cellularization, neither cyclin is completely degraded upon the metaphase-anaphase transition.

Characterization of a candidate bcl-1 gene

The t(11;14)(q13;q32) translocation has been associated with human B-lymphocytic malignancy. Several examples of this translocation have been cloned, documenting that this abnormality joins the immunoglobulin heavy-chain gene to the bcl-1 locus on chromosome 11. However, the identification of the bcl-1 gene, a putative dominant oncogene, has been elusive. In this work, we have isolated genomic clones covering 120 kb of the bcl-1 locus. Probes from the region of an HpaII-tiny-fragment island identified a candidate bcl-1 gene. cDNAs representing the bcl-1 mRNA were cloned from three cell lines, two with the translocation. The deduced amino acid sequence from these clones showed bcl-1 to be a member of the cyclin gene family. In addition, our analysis of expression of bcl-1 in an extensive panel of human cell lines showed it to be widely expressed except in lymphoid or myeloid lineages. This observation may provide a molecular basis for distinct modes of cell cycle control in different mammalian tissues. Activation of the bcl-1 gene may be oncogenic by directly altering progression through the cell cycle.

Characterization of a candidate bcl-1 gene

The t(11;14)(q13;q32) translocation has been associated with human B-lymphocytic malignancy. Several examples of this translocation have been cloned, documenting that this abnormality joins the immunoglobulin heavy-chain gene to the bcl-1 locus on chromosome 11. However, the identification of the bcl-1 gene, a putative dominant oncogene, has been elusive. In this work, we have isolated genomic clones covering 120 kb of the bcl-1 locus. Probes from the region of an HpaII-tiny-fragment island identified a candidate bcl-1 gene. cDNAs representing the bcl-1 mRNA were cloned from three cell lines, two with the translocation. The deduced amino acid sequence from these clones showed bcl-1 to be a member of the cyclin gene family. In addition, our analysis of expression of bcl-1 in an extensive panel of human cell lines showed it to be widely expressed except in lymphoid or myeloid lineages. This observation may provide a molecular basis for distinct modes of cell cycle control in different mammalian tissues. Activation of the bcl-1 gene may be oncogenic by directly altering progression through the cell cycle.