SARIFA as a new histopathological biomarker is associated with adverse clinicopathological characteristics, tumor-promoting fatty-acid metabolism, and might predict a metastatic pattern in pT3a prostate cancer

BACKGROUND

Recently, we introduced Stroma-AReactive-Invasion-Front-Areas (SARIFA) as a novel hematoxylin-eosin (H&E)-based histopathologic prognostic biomarker for various gastrointestinal cancers, closely related to lipid metabolism. To date, no studies on SARIFA, which is defined as direct tumor-adipocyte-interaction, beyond the alimentary tract exist. Hence, the objective of our current investigation was to study the significance of SARIFA in pT3a prostate cancer (PCa) and explore its association with lipid metabolism in PCa as lipid metabolism plays a key role in PCa development and progression.

METHODS

To this end, we evaluated SARIFA-status in 301 radical prostatectomy specimens and examined the relationship between SARIFA-status, clinicopathological characteristics, overall survival, and immunohistochemical expression of FABP4 and CD36 (proteins closely involved in fatty-acid metabolism). Additionally, we investigated the correlation between SARIFA and biochemical recurrence-free survival (BRFS) and PSMA-positive recurrences in PET/CT imaging in a patient subgroup. Moreover, a quantitative SARIFA cut-off was established to further understand the underlying tumor biology.

RESULTS

SARIFA positivity occurred in 59.1% (n = 178) of pT3a PCas. Our analysis demonstrated that SARIFA positivity is strongly associated with established high-risk features, such as R1 status, extraprostatic extension, and higher initial PSA values. Additionally, we observed an upregulation of immunohistochemical CD36 expression specifically at SARIFAs (p = 0.00014). Kaplan-Meier analyses revealed a trend toward poorer outcomes, particularly in terms of BRFS (p = 0.1). More extensive tumor-adipocyte interaction, assessed as quantity-dependent SARIFA-status on H&E slides, is also significantly associated with high-risk features, such as lymph node metastasis, and seems to be associated with worse survival outcomes (p = 0.16). Moreover, SARIFA positivity appeared to be linked to more distant lymph node and bone metastasis, although statistical significance was slightly not achieved (both p > 0.05).

CONCLUSIONS

This is the first study to introduce SARIFA as easy-and-fast-to-assess H&E-based biomarker in locally advanced PCa. SARIFA as the histopathologic correlate of a distinct tumor biology, closely related to lipid metabolism, could pave the way to a more detailed patient stratification and to the development of novel drugs targeting lipid metabolism in pT3a PCa. On the basis of this biomarker discovery study, further research efforts on the prognostic and predictive role of SARIFA in PCa can be designed.

Making the COVID-19 crisis a real opportunity for environmental sustainability

An optimistic narrative has gained momentum during the first year of the pandemic: the COVID-19 crisis may have opened a window of opportunity to "rebuild better", to spur societal transitions towards environmental sustainability. In this comment, we review first evidence of individual and political changes made so far. Findings suggest that economies worldwide are not yet building back better. Against this background, we argue that a naïve opportunity narrative may even impair the progress of transitions towards environmental sustainability because it may render green recovery measures ineffective, costly, or infeasible. Based on these observations, we derive conditions for green recovery policies to succeed. They should consist of a policy mix combining well-targeted green subsidies with initiatives to price emissions and scrap environmentally harmful subsidies. Moreover, green recovery policies must be embedded into a narrative that avoids trading off environmental sustainability with other domains of sustainability-and rather highlights respective synergies that can be realized when recovering from the COVID-19 crisis.

Case Report: Daratumumab in a Patient With Severe Refractory Anti-NMDA Receptor Encephalitis

Anti-NMDA receptor encephalitis is the most common type of antibody mediated autoimmune encephalitis (AIE). Patients often develop neuropsychiatric symptoms and seizures, women are affected about four times more than men, and in about 50% the disease is associated with a neoplasia, especially teratomas of the ovary. We describe the case of a 20-year-old woman suffering from a severe therapy refractory course of anti-NMDA receptor encephalitis. Treatment included glucocorticoids, plasma exchange, intravenous immunoglobulins, rituximab, and bortezomib without clinical improvement. Due to a therapy refractive course 28 weeks after disease onset, the patient received 10 cycles of daratumumab. Therapy escalation was performed with the anti-CD38 monoclonal antibody daratumumab as off label treatment, based on the therapy of refractory myeloma and led to an improvement of her clinical status. She spent about 200 days on the intensive care unit, followed by several weeks on the intermediate care unit with close follow ups every 4–6 weeks afterward. During follow-up, the patient was able to resume everyday and self-care activities, reflected by the modified Rankin scale (mRS) and Barthel index. Because this disease is potentially life threatening and can lead to irreversible brain atrophy, development of further therapy strategies are of great importance. Our case describes a successful treatment for therapy refractory anti-NMDA receptor encephalitis using the anti-CD38 antibody daratumumab.

The lncRNA lincNMR regulates nucleotide metabolism via a YBX1 - RRM2 axis in cancer

Long intergenic non-coding RNA-Nucleotide Metabolism Regulator (lincNMR) is a long non-coding RNA (lncRNA) which is induced in hepatocellular carcinoma. Its depletion invokes a proliferation defect, triggers senescence and inhibits colony formation in liver, but also breast and lung cancer cells. Triple-label SILAC proteomics profiles reveal a deregulation of key cell cycle regulators in lincNMR-depleted cells like the key dNTP synthesizing enzymes RRM2, TYMS and TK1, implicating lincNMR in regulating nucleotide metabolism. LincNMR silencing decreases dNTP levels, while exogenous dNTPs rescues the proliferation defect induced by lincNMR depletion. In vivo RNA Antisense Purification (RAP-MS) identifies YBX1 as a direct interaction partner of lincNMR which regulates RRM2, TYMS and TK1 expression and binds to their promoter regions. In a Chick Chorioallantoic Membrane (CAM) in vivo model, lincNMR-depleted tumors are significantly smaller. In summary, we discover a lincRNA, lincNMR, which regulates tumor cell proliferation through a YBX1-RRM2-TYMS-TK1 axis governing nucleotide metabolism.

[COVID-19 pandemic: structured expansion of ventilation capacities using home respirators]

Due to the current COVID-19 pandemic there is a need for a rapid increase in intensive care and ventilation capacities. Delivery times for additional intensive care respirators are currently not foreseeable. An option to increase ventilation capacities not only for COVID-19, but for all patients requiring mechanical ventilation is to use home respirators. Home respirators are turbine respirators, so they can usually be operated without high-pressure oxygen connections and can therefore also be used in areas outside the classical intensive care medical infrastructure. Due to their limited technical features, home respirators are not suitable for the treatment of severely affected patients but can be used for weaning after respiratory improvement, which means that intensive care respirators are available again more quickly. Respiratory therapists are specially trained nurses or therapists in the field of out of hospital ventilation and can independently use home ventilation respirators, for example for weaning in the intensive care unit. Thus, they relieve intensive care nursing staff in the pandemic. Due to the COVID-19 pandemic medical students from the Oldenburg University are currently being trained in operating home respirators to provide basic support in the hospital if necessary.

Passive Ballistic Microbunching of Nonultrarelativistic Electron Bunches Using Electromagnetic Wakefields in Dielectric-Lined Waveguides

Temporally modulated electron beams have a wide array of applications ranging from the generation of coherently enhanced electromagnetic radiation to the resonant excitation of electromagnetic wakefields in advanced-accelerator concepts. Likewise producing low-energy ultrashort microbunches could be useful for ultrafast electron diffraction and new accelerator-based light-source concepts. In this Letter we propose and experimentally demonstrate a passive microbunching technique capable of forming a picosecond bunch train at ∼6  MeV. The method relies on the excitation of electromagnetic wakefields as the beam propagates through a dielectric-lined waveguide. Owing to the nonultrarelativistic nature of the beam, the induced energy modulation eventually converts into a density modulation as the beam travels in a following free-space drift. The modulated beam is further accelerated to ∼20  MeV while preserving the imparted density modulation.

Targeting LINC00673 expression triggers cellular senescence in lung cancer

Aberrant expression of noncoding RNAs plays a critical role during tumorigenesis. To uncover novel functions of long non-coding RNA (lncRNA) in lung adenocarcinoma, we used a microarray-based screen identifying LINC00673 with elevated expression in matched tumor versus normal tissue. We report that loss of LINC00673 is sufficient to trigger cellular senescence, a tumor suppressive mechanism associated with permanent cell cycle arrest, both in lung cancer and normal cells in a p53-dependent manner. LINC00673-depleted cells fail to efficiently transit from G1- to S-phase. Using a quantitative proteomics approach, we confirm the modulation of senescence-associated genes as a result of LINC00673 knockdown. In addition, we uncover that depletion of p53 in normal and tumor cells is sufficient to overcome LINC00673-mediated cell cycle arrest and cellular senescence. Furthermore, we report that overexpression of LINC00673 reduces p53 translation and contributes to the bypass of Ras-induced senescence. In summary, our findings highlight LINC00673 as a crucial regulator of proliferation and cellular senescence in lung cancer.

The Long Noncoding RNA Cancer Susceptibility 9 and RNA Binding Protein Heterogeneous Nuclear Ribonucleoprotein L Form a Complex and Coregulate Genes Linked to AKT Signaling

The identification of viability-associated long noncoding RNAs (lncRNAs) might be a promising rationale for new therapeutic approaches in liver cancer. Here, we applied an RNA interference screening approach in hepatocellular carcinoma (HCC) cell lines to find viability-associated lncRNAs. Among the multiple identified lncRNAs with a significant impact on HCC cell viability, we selected cancer susceptibility 9 (CASC9) due to the strength of its phenotype, expression, and up-regulation in HCC versus normal liver. CASC9 regulated viability across multiple HCC cell lines as shown by clustered regularly interspaced short palindromic repeats interference and single small interfering RNA (siRNA)-mediated and siRNA pool-mediated depletion of CASC9. Further, CASC9 depletion caused an increase in apoptosis and a decrease of proliferation. We identified the RNA binding protein heterogeneous nuclear ribonucleoprotein L (HNRNPL) as a CASC9 interacting protein by RNA affinity purification and validated it by native RNA immunoprecipitation. Knockdown of HNRNPL mimicked the loss-of-viability phenotype observed upon CASC9 depletion. Analysis of the proteome (stable isotope labeling with amino acids in cell culture) of CASC9-depleted and HNRNPL-depleted cells revealed a set of coregulated genes which implied a role of the CASC9:HNRNPL complex in AKT signaling and DNA damage sensing. CASC9 expression levels were elevated in patient-derived tumor samples compared to normal control tissue and had a significant association with overall survival of HCC patients. In a xenograft chicken chorioallantoic membrane model, we measured decreased tumor size after knockdown of CASC9. Conclusion: Taken together, we provide a comprehensive list of viability-associated lncRNAs in HCC; we identified the CASC9:HNRNPL complex as a clinically relevant viability-associated lncRNA/protein complex which affects AKT signaling and DNA damage sensing in HCC.

A cautionary tale of sense-antisense gene pairs: independent regulation despite inverse correlation of expression

Long non-coding RNAs (lncRNAs) have been proven to play important roles in diverse cellular processes including the DNA damage response. Nearly 40% of annotated lncRNAs are transcribed in antisense direction to other genes and have often been implicated in their regulation via transcript- or transcription-dependent mechanisms. However, it remains unclear whether inverse correlation of gene expression would generally point toward a regulatory interaction between the genes. Here, we profiled lncRNA and mRNA expression in lung and liver cancer cells after exposure to DNA damage. Our analysis revealed two pairs of mRNA-lncRNA sense-antisense transcripts being inversely expressed upon DNA damage. The lncRNA NOP14-AS1 was strongly upregulated upon DNA damage, while the mRNA for NOP14 was downregulated, both in a p53-dependent manner. For another pair, the lncRNA LIPE-AS1 was downregulated, while its antisense mRNA CEACAM1 was upregulated. To test whether as expected the antisense genes would regulate each other resulting in this highly significant inverse correlation, we employed antisense oligonucleotides and RNAi to study transcript-dependent effects as well as dCas9-based transcriptional modulation by CRISPRi/CRISPRa for transcription-dependent effects. Surprisingly, despite the strong stimulus-dependent inverse correlation, our data indicate that neither transcript- nor transcription-dependent mechanisms explain the inverse regulation of NOP14-AS1:NOP14 or LIPE-AS1:CEACAM1 expression. Hence, sense-antisense pairs whose expression is strongly—positively or negatively—correlated can be nonetheless regulated independently. This highlights the requirement of individual experimental studies for each antisense pair and prohibits drawing conclusions on regulatory mechanisms from expression correlations.

Challenges of CRISPR/Cas9 applications for long non-coding RNA genes

The CRISPR/Cas9 system provides a revolutionary genome editing tool for all areas of molecular biology. In long non-coding RNA (lncRNA) research, the Cas9 nuclease can delete lncRNA genes or introduce RNA-destabilizing elements into their locus. The nuclease-deficient dCas9 mutant retains its RNA-dependent DNA-binding activity and can modulate gene expression when fused to transcriptional repressor or activator domains. Here, we systematically analyze whether CRISPR approaches are suitable to target lncRNAs. Many lncRNAs are derived from bidirectional promoters or overlap with promoters or bodies of sense or antisense genes. In a genome-wide analysis, we find only 38% of 15929 lncRNA loci are safely amenable to CRISPR applications while almost two-thirds of lncRNA loci are at risk to inadvertently deregulate neighboring genes. CRISPR- but not siPOOL or Antisense Oligo (ASO)-mediated targeting of lncRNAs NOP14-AS1, LOC389641, MNX1-AS1 or HOTAIR also affects their respective neighboring genes. Frequently overlooked, the same restrictions may apply to mRNAs. For example, the tumor suppressor TP53 and its head-to-head neighbor WRAP53 are jointly affected by the same sgRNAs but not siPOOLs. Hence, despite the advantages of CRISPR/Cas9 to modulate expression bidirectionally and in cis, approaches based on ASOs or siPOOLs may be the better choice to target specifically the transcript from complex loci.

The long non-coding RNA LINC00152 is essential for cell cycle progression through mitosis in HeLa cells

In recent years, long non-coding RNA (lncRNA) research has identified essential roles of these transcripts in virtually all physiological cellular processes including tumorigenesis, but their functions and molecular mechanisms are poorly understood. In this study, we performed a high-throughput siRNA screen targeting 638 lncRNAs deregulated in cancer entities to analyse their impact on cell division by using time-lapse microscopy. We identified 26 lncRNAs affecting cell morphology and cell cycle including LINC00152. This transcript was ubiquitously expressed in many human cell lines and its RNA levels were significantly upregulated in lung, liver and breast cancer tissues. A comprehensive sequence analysis of LINC00152 revealed a highly similar paralog annotated as MIR4435-2HG and several splice variants of both transcripts. The shortest and most abundant isoform preferentially localized to the cytoplasm. Cells depleted of LINC00152 arrested in prometaphase of mitosis and showed reduced cell viability. In RNA affinity purification (RAP) studies, LINC00152 interacted with a network of proteins that were associated with M phase of the cell cycle. In summary, we provide new insights into the properties and biological function of LINC00152 suggesting that this transcript is crucial for cell cycle progression through mitosis and thus, could act as a non-coding oncogene.

Adhesion and activation of platelets from subjects with coronary artery disease and apparently healthy individuals on biomaterials

On the basis of the clinical studies in patients with coronary artery disease (CAD) presenting an increased percentage of activated platelets, we hypothesized that hemocompatibility testing utilizing platelets from healthy individuals may result in an underestimation of the materials' thrombogenicity. Therefore, we investigated the interaction of polymer-based biomaterials with platelets from CAD patients in comparison to platelets from apparently healthy individuals. In vitro static thrombogenicity tests revealed that adherent platelet densities and total platelet covered areas were significantly increased for the low (polydimethylsiloxane, PDMS) and medium (Collagen) thrombogenic surfaces in the CAD group compared to the healthy subjects group. The area per single platelet-indicating the spreading and activation of the platelets-was markedly increased on PDMS treated with PRP from CAD subjects. This could not be observed for collagen or polytetrafluoroethylene (PTFE). For the latter material, platelet adhesion and surface coverage did not differ between the two groups. Irrespective of the substrate, the variability of these parameters was increased for CAD patients compared to healthy subjects. This indicates a higher reactivity of platelets from CAD patients compared to the healthy individuals. Our results revealed, for the first time, that utilizing platelets from apparently healthy donors bears the risk of underestimating the thrombogenicity of polymer-based biomaterials.

S3-Guidelines for the Treatment of Inflammatory Breast Disease during the Lactation Period: AWMF Guidelines, Registry No. 015/071 (short version) AWMF Leitlinien-Register Nr. 015/071 (Kurzfassung)

Breastfeeding is widely acknowledged to be the best and most complete form of nutrition for healthy infants born at term and is associated with numerous benefits in terms of infants' health, growth, immunity and development. However, breastfeeding problems often result in early weaning. Standardized treatment recommendations for breastfeeding-related diseases are necessary to optimize the care offered to breastfeeding women. Evidence and consensus based guidelines for the treatment of puerperal mastitis, sore nipples, engorgement and blocked ducts were developed on the initiative of the National Breastfeeding Committee. These guidelines were developed in accordance with the criteria set up by the Arbeitsgemeinschaft der Wissenschaftlichen Medizinischen Fachgesellschaften (AWMF), the Association of Scientific Medical Societies in Germany. The recommendations were drawn up by an interdisciplinary group of experts and were based on a systematic search and evaluation of the literature but also took clinical experience into account. Additionally good clinical practice (GCP) in terms of expert opinion was formulated in cases where scientific investigations could not be performed or were not aimed for. This article presents a summary of the recommendations of the S3-guidelines.

Abstract 1121: The long non-coding RNA MALAT1 is an essential gene regulator for lung cancer metastasis in a novel human knockout model

The long non-coding RNA MALAT1 was one of the first lncRNAs associated with cancer: it is a highly conserved nuclear ncRNA and a predictive marker for metastasis development in lung cancer. However, its high abundance and nuclear localization have greatly hampered its functional analysis since it is only inefficiently knocked down by RNA interference (RNAi).

To uncover its functional importance, we developed a MALAT1 knockout model in human lung tumor cells by genomically integrating RNA destabilizing elements site-specifically into the MALAT1 locus using Zinc Finger Nucleases (ZFN).This approach yielded a more than 1000-fold silencing of MALAT1 providing a unique loss-of-function model.

Proposed mechanisms of action of MALAT1 include regulation of splicing or gene expression. In lung cancer, MALAT1 does not alter alternative splicing but actively regulates gene expression inducing a signature of metastasis-associated genes. Consequently, MALAT1-deficient cells are impaired in migration and form fewer tumor nodules in a mouse xenograft model.

Encouraged by this discovery of the essential function of MALAT1 in lung cancer metastasis, we wanted to analyze whether MALAT1 could also be therapeutically targeted: We developed Antisense oligonucleotides (ASOs) effectively blocking MALAT1 expression in the cell culture and in the animal. Notably, MALAT1-ASO treatment prevents metastasis formation after tumor implantation. Thus, targeting MALAT1 with antisense oligonucleotides provides a potential therapeutic approach to prevent lung cancer metastasis with MALAT1 serving as both, predictive marker and therapeutic target.

Lastly, regulating gene expression, but not alternative splicing is the critical function of MALAT1 in lung cancer metastasis.

In summary, ten years after the discovery of the lncRNA MALAT1 as a biomarker for lung cancer metastasis, our loss-of-function model unravels the active function of MALAT1 as a regulator of gene expression governing hallmarks of lung cancer metastasis.

Citation Format: Tony Gutschner, Monika Hämmerle, Moritz Eißmann, Jeff Hsu, Youngsoo Kim, Gene Hung, Alexey Revenko, Gayatri Arun, Marion Stentrup, Matthias Groß, Martin Zörnig, A. Robert MacLeod, David L. Spector, Sven Diederichs. The long non-coding RNA MALAT1 is an essential gene regulator for lung cancer metastasis in a novel human knockout model . [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1121. doi:10.1158/1538-7445.AM2013-1121

Loss of the abundant nuclear non-coding RNA MALAT1 is compatible with life and development

The metastasis-associated lung adenocarcinoma transcript 1, MALAT1, is a long non-coding RNA (lncRNA) that has been discovered as a marker for lung cancer metastasis. It is highly abundant, its expression is strongly regulated in many tumor entities including lung adenocarcinoma and hepatocellular carcinoma as well as physiological processes, and it is associated with many RNA binding proteins and highly conserved throughout evolution. The nuclear transcript MALAT-1 has been functionally associated with gene regulation and alternative splicing and its regulation has been shown to impact proliferation, apoptosis, migration and invasion.   Here, we have developed a human and a mouse knockout system to study the loss-of-function phenotypes of this important ncRNA. In human tumor cells, MALAT1 expression was abrogated using Zinc Finger Nucleases. Unexpectedly, the quantitative loss of MALAT1 did neither affect proliferation nor cell cycle progression nor nuclear architecture in human lung or liver cancer cells. Moreover, genetic loss of Malat1 in a knockout mouse model did not give rise to any obvious phenotype or histological abnormalities in Malat1-null compared with wild-type animals. Thus, loss of the abundant nuclear long ncRNA MALAT1 is compatible with cell viability and normal development.

Abstract A21: MALAT-1 is essential for lung cancer metastasis in a novel human knockout model

The highly conserved long non-coding RNA MALAT-1 (Metastasis-Associated in Lung Adenocarcinoma Transcript 1) had been discovered as a prognostic marker associated with poor survival and development of distant metastasis in lung adenocarcinoma. Since then, it has been found to be deregulated in numerous tumor entities and has been linked to splicing. However, its functional relevance in tumor cells remains to be elucidated. Knockdown models for MALAT1 have been described but suffer from insufficient silencing efficiency of the highly abundant, nuclear non-coding RNA (ncRNA).

In this project, we have developed a novel strategy to create ncRNA knockouts in human cancer cell lines. We have successfully used a synthetic Zinc Finger Nuclease engineered to target the 5′-region of MALAT1 to stably and biallelically integrate RNA-destabilizing elements into the genome of human lung cancer cells (A549). This approach resulted in a specific and more than 1000-fold silencing of MALAT1 in individual clones compared to a less than 5-fold silencing using siRNAs. Thus, this approach can be used to create functional knockouts of coding as well as non-coding genes also in human tumor cell lines allowing loss-of-function studies also of non-conserved ncRNAs in the future.

Phenotypically, the MALAT1-Knockout cells (KO) greatly differ from their parental cell line and wildtype clones (WT): Next to morphological changes, the migration of the KO cells is largely impaired as shown in scratch assays. In xenograft assays after i.v. injection, the KO cells form significantly fewer and smaller lung metastases than their WT counterparts. Since no large difference was observed after subcutaneous injection of the WT and the KO cells, this indicates a specific, active and essential function of MALAT1 in metastasis.

Exon microarrays of the WT and KO cell lines have revealed multiple migration- or metastasis-associated transcripts deregulated by loss of MALAT1 and hence potential target genes. These analyses also uncovered, that splicing is likely not the only functional mechanism of MALAT1 in the nucleus.

Taken together, we have developed a novel, highly effective approach for the knockout of genes that can be used for non-coding as well as coding RNAs in human tumor cells as well as cells from other species. Knockout of MALAT1 in human lung cancer cells revealed its essential function in metastasis as well as genes directly and indirectly targeted by MALAT1.

Citation Format: Tony Gutschner, Moritz Eißmann, Monika Hämmerle, Marion Stentrup, Catherina Hildenbrandt, Matthias Groß, Martin Zörnig, Sven Diederichs. MALAT-1 is essential for lung cancer metastasis in a novel human knockout model [abstract]. In: Proceedings of the AACR Special Conference on Noncoding RNAs and Cancer; 2012 Jan 8-11; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(2 Suppl):Abstract nr A21.

Influence of sugars on blue light-induced synthesis of chlorophyll in cultured plant cells

In supension cultured tobacco cells only blue light induces and maintains chlorophyll synthesis if the liquid nutrient medium is supplemented with sucrose. The yield per gram fresh weight is closely correlated with the energy fluence rate of blue light, but not with the initial amount of sucrose added to the medium (3-12 g/l). The uptake of sucrose by the cells proceeds with a constant rate over the growth period independently of the initial amount leading within 10-25 days to sucrose-free media. Under these conditions the cells continue to synthesize chlorophyll for about 10 days. This limitation is overcome by adding sucrose to the medium at equal time intervals thus establishing a constant sugar level beyond the growth period. In contrast, glucose as carbon source cannot adequately replace sucrose in inducing and maintaining blue light-induced chlorophyll synthesis. Depending on the initial amount (3-10 g/l) this sugar is rapidly disappearing from the medium within 1-5 days after inoculation of the cells. It apparently serves as a preferential source of energy and carbon skeletons thus suppressing chlorophyll synthesis. On the other hand, glucose combined with sucrose in the medium brings about the characteristic induction and accumulation of chlorophyll in blue light which is observed with sucrose as the sole carbon source.