Biology subjects

Franco, E.

Publications and source records attributed to Franco, E..

At least 19 recordsLinked to original sources

bioRxiv2026

Programming the Internal Architecture of Synthetic Compartments by Coassembling Filamentous and Liquid DNA Phases

Living cells rely on filaments and condensates as key organizers of their interior. Developing these structural primitives together inside synthetic compartments using programmable components is a step toward building functional synthetic cells, composite biomaterials, and synthetic tissues. Here, we demonstrate that DNA nanotubes and DNA condensates can be co-assembled within cell-sized compartments, including water-in-oil droplets and giant unilamellar vesicles (GUVs). The two nanostructures form as expected, producing a single condensate surrounded by nanotubes in diverse morphologies that depend on DNA and salt concentration, as well as compartment size. By incorporating photoactivatable DNA linkers, we can control the order of assembly and trigger reconfiguration of nanotube networks into ring-shaped bundles enclosing a condensate, architectures reminiscent of a cellular nucleus within a cytoskeletal ring. An isothermal assembly protocol based on monovalent salts further extends this approach to GUVs. Together, these results establish DNA filaments and condensates as programmable, composable organizers of synthetic cell interiors.

synthetic biology↗

bioRxiv2026

Programmable artificial RNA condensates in mammalian cells

Artificial biomolecular condensates have emerged as powerful tools to control cellular behaviors. Here we introduce a method to build artificial condensates within living mammalian cells through the design of modular RNA motifs formed by a single, short strand of RNA. These condensates emerge spontaneously, creating RNA-rich compartments that remain separated from their surrounding environment. The RNA sequences include stem-loop domains that fold as the RNA is transcribed, and then condense in the nucleus and cytoplasm through loop-loop interactions. These sequences can be optimized and diversified, enabling the generation of distinct, non-mixing condensate populations and the programmable control of their subcellular localization. The RNA motifs can also be modified to recruit small molecules, proteins, and RNA molecules in a sequence-specific manner to the RNA-rich phase. By introducing additional RNAs that link two distinct types of condensates, we can create droplets with multiple subcompartments, whose organization can be controlled by tuning the stoichiometry of different RNA sequences. These artificial condensates provide a versatile platform for studying and manipulating molecular functions inside living cells.

synthetic biology↗

bioRxiv2025

It runs in the family: Discovery of enzymes in the oleuropein pathway in Olive (Olea europaea) by comparative transcriptomics

Olive (Olea europaea L.) is one of the most important crop trees, with olive oil being a key ingredient of the Mediterranean diet. Oleuropein, an oleoside-type secoiridoid, is the major determinant of flavor and quality of olive oil. Iridoid biosynthesis has been elucidated in Catharanthus roseus, which produces secologanin-type secoiridoids, but iridoid biosynthesis in other species remains unresolved. In this work, we sequenced RNA from olive fruit mesocarp of six commercial olive cultivars with varying oleuropein content, during maturation and ripening. Using this data we discovered three polyphenol oxidases with oleuropein synthase (OS) activity, a novel oleoside-11-methyl ester glucosyl transferase (OMEGT) synthesizing a potential intermediate in the route, and a 7-epi-loganic acid O-methyltransferase (7eLAMT). Interestingly, integrating transcriptomics data from 15 plant species from three iridoid-producing plant orders (Lamiales, Gentianales, and Cornales), and tissue expression panels from Jasminum sambac and Fraxinus excelsior, we discovered two 2-oxoglutarate dependent dioxygenases (named 7eLAS) that synthesize 7-epi-loganic acid; in contrast C. roseus 7-deoxy-loganic acid hydroxylase (7DLH), a known bottleneck in MIA production, is a cytochrome p450. This comparative co-expression method, which combines guilt by association and comparative transcriptomics approaches, can successfully leverage big datasets for untargeted discovery of enzymes. Key FindingsO_LIExpression of genes involved in iridoid biosynthesis, from the early MEP pathway to the last step of oleuropein biosynthesis, decreases during olive fruit maturation. C_LIO_LIWe discovered an oxoglutarate dependent dioxygenase, 7-epi-loganic acid synthase (7eLAS), catalyzing the stereoselective oxidation of 7-deoxy-loganic acid to 7-epi-loganic acid, in a reaction analogous to C. roseus 7-deoxy-loganic acid hydroxylase (7DLH), a cytochrome p450. C_LIO_LIWe report a 7-epi-loganic acid O-methyltransferase (7eLAMT) orthologous to Catharanthus roseus loganic acid O-methyltransferase and found a novel oleoside-11-methyl ester glucosyl transferase (OMEGT) synthesizing 7-{beta}-1-D-glucopyranosyl-oleoside-11-methyl ester, a potential intermediate in the oleuropein biosynthesis route. C_LIO_LIWe discovered three olive polyphenol oxidases that have oleuropein synthase (OS) activity, catalyzing the conversion of ligstroside to oleuropein. C_LI

biochemistry↗

bioRxiv2025

Internal phase separation in synthetic DNA condensates

Biomolecular condensates regulate cellular biochemistry by organizing enzymes, substrates and metabolites, and often acquire partially de-mixed states whereby distinct internal domains play functional roles. Despite their physiological relevance, questions remain about the principles underpinning the emergence of multi-phase condensates. Here, we present a model system of synthetic DNA nanostructures able to form monophasic or biphasic condensates. Key condensate features, including the degree of interphase mixing and the relative size and spatial arrangement of domains, can be controlled by altering nanostructure stoichiometries. The modular nature of the system facilitates an intuitive understanding of phase behavior, and enables mapping of the experimental phenomenology onto a predictive Flory-Huggins model. The experimental and theoretical framework we introduce will help address open questions on multiphase condensation in biology and aid the design of functional biomolecular condensates in vitro, in synthetic cells, and in living cells.

biophysics↗

bioRxiv2025

Temporal dose inversion properties of adaptive biomolecular circuits

Cells have the capacity to encode and decode information in the temporal features of molecular signals. Many pathways, for example, generate either sustained or pulsatile responses depending on the context, and such diverse temporal behaviors have a profound impact on cell fate. Here we focus on how molecular pathways can convert the temporal features of dynamic signals, in particular how they can convert transient signals into persistent downstream events and vice versa. We refer to this type of behavior as temporal dose inversion, and we demonstrate that it can be achieved through adaptive molecular circuits. Using a cell-free synthetic gene circuit implementing an incoherent feedforward loop (IFFL), we experimentally demonstrate the temporal dose inversion. To understand the design principles of the temporal dose inversion, we analyze adaptive circuit motifs including incoherent feedforward loops (IFFLs) and negative feedback loops (NFLs). Through numerical simulations with expensive parameter exploration, we identify parametric regimes in which these circuits exhibit temporal dose inversion. We further examine more detailed biological models of the IFFL and NFL circuits, including enzymatic signaling models and gene regulatory network models, showing that the IFFL circuits is more likely to exhibit temporal dose inversion compared with the NFL circuits. Finally, we analyze a generalized IFFL topology, and we find that both the time delay in the inhibition pathway and the relative signal intensities of the activation and inhibition signals are key determinants for temporal dose inversion. Together, our results establish a design principle of temporal dose inversion on the adaptive biomolecular circuits and provide mechanistic insight into how molecular networks process temporal information in dynamic signals.

systems biology↗

bioRxiv2024

Design of an intracellular aptamer-based fluorescent biosensor to track burden in E. coli

Cell burden impacts the performance of engineered synthetic systems. For this reason, there is great interest toward the development of tools to track burden and improve biotechnology applications. Fluorogenic RNA aptamers are excellent candidates for live monitoring of burden because their production is expected to impose a negligible load on transcription resources. Here we characterise the performance of a library of aptamers when expressed from different promoters in E. coli. We find that aptamer relative performance is dependent on the promoter and the strain, and that, contrary to expectation, aptamer expression impacts host fitness. By selecting two of the aptamers with brighter output and lower impact, we then design an intracellular biosensor able to report on the activation of the burden response in engineered cells. The sensor developed here adds to the collection of tools available for burden mitigation and may support bioprocessing applications where improved host performance is sought.

synthetic biology↗

bioRxiv2024

Protein recruitment to dynamic DNA-RNA host condensates

We describe the design and characterization of artificial nucleic acid condensates that are engineered to recruit and locally concentrate proteins of interest in vitro. These condensates emerge from the programmed interactions of nanostructured motifs assembling from three DNA strands and one RNA strand that can include an aptamer domain for the recruitment of a target protein. Because condensates are designed to form regardless of the presence of target protein, they function as "host" compartments. As a model protein we consider streptavidin (SA) due to its widespread use in binding assays, thus the host condensates presented here could find immediate use for the physical separation of a variety of biotin-tagged components. In addition to demonstrating protein recruitment, we describe two approaches to control the onset of condensation and protein recruitment. The first approach uses UV irradiation, a physical stimulus that bypasses the need for exchanging molecular inputs and is particularly convenient to control condensation in emulsion droplets. The second approach uses RNA transcription, a ubiquitous biochemical reaction that is central to the development of the next generation of living materials. We finally show that the combination of RNA transcription and degradation leads to an autonomous dissipative system in which host condensates and protein recruitment occur transiently, and that the host condensate size as well as the timescale of the transient can be controlled by the level of RNA degrading enzyme. For Table of Contents Only O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=109 SRC="FIGDIR/small/597281v1_ufig1.gif" ALT="Figure 1"> View larger version (22K): org.highwire.dtl.DTLVardef@1f6dc00org.highwire.dtl.DTLVardef@1e5a9eforg.highwire.dtl.DTLVardef@f7c247org.highwire.dtl.DTLVardef@1f3c3d0_HPS_FORMAT_FIGEXP M_FIG C_FIG

synthetic biology↗

bioRxiv2024

Design of a sequestration-based network with tunable pulsing dynamics

Incoherent feedforward networks exhibit the ability to generate temporal pulse behavior. However, exerting control over specific dynamic properties, such as amplitude and rise time, poses a challenge and is intricately tied to the networks implementation. In this study, we focus on analyzing sequestration-based networks capable of exhibiting pulse behavior. By employing time-scale separation in the fast sequestration regime, we approximate the temporal dynamics of these networks. This approach allows us to establish a mapping that elucidates the impact of varying the kinetic rates and pulse specifications, including amplitude and rise time. Furthermore, we introduce a positive feedback mechanism to regulate the amplitude of the pulsing response.

synthetic biology↗

bioRxiv2024

Neural networks built from enzymatic reactions can operate as linear and nonlinear classifiers

The engineering of molecular programs capable of processing patterns of multi-input biomarkers holds great potential in applications ranging from in vitro diagnostics (e.g., viral detection, including COVID-19) to therapeutic interventions (e.g., discriminating cancer cells from normal cells). For this reason, mechanisms to design molecular networks for pattern recognition are highly sought after. In this work, we explore how enzymatic networks can be used for both linear and nonlinear classification tasks. By leveraging steady-state analysis and showing global stability, we demonstrate that these networks can function as molecular perceptrons, fundamental units of artificial neural networks--capable of processing multiple inputs associated with positive and negative weights to achieve linear classification. Furthermore, by composing orthogonal enzymatic reactions, we show that multi-layer networks can be constructed to achieve nonlinear classification.

synthetic biology↗

bioRxiv2024

Developmental assembly of multi-component polymer systems through interconnected gene networks in vitro

Living cells regulate the dynamics of developmental events through interconnected signaling systems that activate and deactivate inert precursors. This suggests that similarly, synthetic biomaterials could be designed to develop over time by using chemical reaction networks to regulate the availability of assembling components. Here we demonstrate how the sequential activation or deactivation of distinct DNA building blocks can be modularly coordinated to form distinct populations of self-assembling polymers using a transcriptional signaling cascade of synthetic genes. Our building blocks are DNA tiles that polymerize into nanotubes, and whose assembly can be controlled by RNA molecules produced by synthetic genes that target the tile interaction domains. To achieve different RNA production rates, we use a strategy based on promoter "nicking" and strand displacement. By changing the way the genes are cascaded and the RNA levels, we demonstrate that we can obtain spatially and temporally different outcomes in nanotube assembly, including random DNA polymers, block polymers, and as well as distinct autonomous formation and dissolution of distinct polymer populations. Our work demonstrates a way to construct autonomous supramolecular materials whose properties depend on the timing of molecular instructions for self-assembly, and can be immediately extended to a variety of other nucleic acid circuits and assemblies.

synthetic biology↗

bioRxiv2024

The unexplored diversity of wild lupins provides rich genomic resources and insights into lupin evolution

Lupin crops provide nutritious seeds as an excellent source of dietary protein. However, extensive genomic resources are needed for the adaptation of lupin crops, particularly to improve their nutritional value and facilitate their adaptation to harsh environments caused by the changing climate. Such resources can be derived from crop wild relatives, which represent a large untapped source of genetic variation for crop improvement. Here we describe the first whole-genome sequences of the cross-compatible species Lupinus cosentinii (Mediterranean) and its pan-Saharan wild relative L. digitatus, which are well adapted to drought-prone environments and partially domesticated. We found that both species are tetraploids, with similar genome structures, distributions of gene duplications, and numbers of expanded and contracted gene families. The expansion and contraction of gene families that determine seed size, a paradigmatic domestication trait, indicates that gene duplication may have led to morphological adaptations in L. cosentinii and L. digitatus differing from those in L. albus, a domesticated lupin used as a reference. Seed size may therefore reflect convergent evolution mechanisms that play a key role in lupin domestication.

plant biology↗

bioRxiv2023

Modular RNA motifs for orthogonal phase separated compartments

Recent discoveries in biology have highlighted the importance of protein and RNA-based condensates as an alternative to classical membrane-bound organelles for the task of compartmentalizing molecules and biochemical reactions. Here, we demonstrate the rational design of pure RNA condensates from star-shaped RNA motifs. We generate condensates using two different RNA nanostar architectures: multi-stranded nanostars whose binding interactions are programmed via single-stranded overhangs, and single-stranded nanostars whose interactions are programmed via kissing loops. Through rational design of the nanostar interaction sequences, we demonstrate that both architectures can produce orthogonal (distinct and immiscible) condensates, which can be individually tracked via fluorogenic aptamers. We also show that aptamers make it possible to recruit peptides and proteins to the condensates with high specificity. Successful cotranscriptional formation of condensates from single-stranded nanostars suggests that they may be genetically encoded and produced in living cells. We provide a library of orthogonal RNA condensates that can be modularly customized and offer a route toward creating systems of functional artificial organelles.

synthetic biology↗

bioRxiv2023

Co-transcriptional production of programmable RNA condensates and synthetic organelles

Condensation of RNA and proteins is central to cellular functions, and the ability to program it would be valuable in synthetic biology and synthetic cell science. Here we introduce a modular platform for engineering synthetic RNA condensates from tailor-made, branched RNA nanostructures that fold and assemble co-transcriptionally. Up to three orthogonal condensates can form simultaneously and selectively accumulate guest molecules. The RNA condensates can be expressed within synthetic cells to produce membrane-less organelles with controlled number, size, morphology and composition, and that display the ability to selectively capture proteins. The in situ expression of programmable RNA condensates could underpin spatial organisation of functionalities in both biological and synthetic cells.

synthetic biology↗

bioRxiv2023

Optimization of RNA Pepper sensors for the detection of arbitrary RNA targets

The development of fluorescent light up RNA aptamers (FLAPs) has paved the way for the creation of sensors to track RNA in live cells. A major challenge with FLAP sensors is their brightness and their limited signal-to-background ratio both in vivo and in vitro. To address this, we develop sensors using the Pepper aptamer, which exhibits superior brightness and photostability when compared to other FLAPs. The sensors are designed to fold into a low fluorescence conformation, and to switch to a high fluorescence conformation through toehold or loop-mediated interactions with their RNA target. Our sensors detect RNA targets as short as 20 nucleotides in length with a wide dynamic range over 300-fold in vitro, and we describe strategies for optimizing the sensors performance for any given RNA targets. To demonstrate the versatility of our design approach, we generate Pepper sensors for a range of specific, biologically relevant RNA sequences. Our design and optimization strategies are portable to other FLAPs, and offer a promising foundation for future development of RNA sensors with high specificity and sensitivity for detecting RNA biomarkers with multiple applications.

biochemistry↗

bioRxiv2023

Building subtraction operators and controllers via molecular sequestration

We show how subtraction can be performed via a simple chemical reaction network that includes molecular sequestration. The network computes the difference between the production rate parameters of the two mutually sequestering species. We benefit from introducing a simple change of variables, that facilitates the derivation of an approximate solution for the differential equations modeling the chemical reaction network, under a time scale separation assumption that is valid when the sequestration rate parameter is sufficiently fast. Our main result is that we provide simple expressions confirming that temporal subtraction occurs when the inputs are constant or time varying. Through simulations, we discuss two sequestration-based architectures for feedback control in light of the subtraction operations they perform.

synthetic biology↗

bioRxiv2023

A portable regulatory RNA array design enables tunable and complex regulation across diverse bacteria

A lack of composable and tunable gene regulators has hindered efforts to engineer non-model bacteria and consortia. To address this, we explore the broad-host potential of small transcription activating RNA (STAR) and propose a novel design strategy to achieve tunable gene control. First, we demonstrate that STARs optimized for E. coli function across different Gram-negative species and can actuate using phage RNA polymerase, suggesting that RNA systems acting at the level of transcription are portable. Second, we explore a novel RNA design strategy that uses arrays of tandem and transcriptionally fused RNA regulators to precisely alter regulator concentration from 1 to 8 copies. This provides a simple means to predictably tune output gain across species and does not require access to large regulatory part libraries. Finally, we show RNA arrays can be used to achieve tunable cascading and multiplexing circuits across species, analogous to the motifs used in artificial neural networks.

synthetic biology↗

bioRxiv2022

Building molecular band-pass filters via molecular sequestration

Engineered genetic circuits with tailored functions that mimic how cells process information in changing environments (e.g. cell fate decision, chemotaxis, immune response) have great applications in biomedicine and synthetic biology. Although there is a lot of progress toward the design of gene circuits yielding desired steady states (e.g. logic-based networks), building synthetic circuits for dynamic signal processing (e.g. filters, frequency modulation, and controllers) is still challenging. Here, we provide a model-based approach to build gene networks that can operate as band-pass filters by taking advantage of molecular sequestration. By suitably approximating the dynamics of molecular sequestration, we analyze an Incoherent Feed-Forward Loop (IFFL) and a Negative Feedback (NF) circuit and illustrate how they can achieve band-pass filter behavior. Computational analysis shows that a circuit that incorporates both IFFL and NF motifs improves the filter performance. Our approach facilitates the design of sequestration-based filters, and may support the synthesis of molecular controllers with desired specifications.

synthetic biology↗

bioRxiv2022

The growth rate of DNA condensate droplets increases with the size of participating subunits

Liquid-liquid phase separation (LLPS) is a common phenomenon underlying the formation of dynamic membraneless organelles in biological cells, which are emerging as major players in controlling cellular functions and health. The bottom-up synthesis of biomolecular liquid systems with simple constituents, like nucleic acids and peptides, is useful to understand LLPS in nature as well as to develop programmable means to build new amorphous materials with properties matching or surpassing those observed in natural condensates. In particular, understanding which parameters determine condensate growth kinetics is essential for the synthesis of condensates with the capacity for active, dynamic behaviors. Here we use DNA nanotechnology to study artificial liquid condensates through programmable star-shaped subunits, focusing on the effects of changing subunit size. First, we show that LLPS is achieved in a six-fold range of subunit size. Second, we demonstrate that the rate of growth of condensate droplets scales with subunit size. Our investigation is supported by a general model that describes how coarsening and coalescence are expected to scale with subunit size under ideal assumptions. Beyond suggesting a route toward achieving control of LLPS kinetics via design of subunit size in synthetic liquids, our work suggests that particle size may be a key parameter in biological condensation processes.

bioengineering↗