Stefano Di Talia, Ph.D. (Rockefeller University)
Control of cell division and differentiation during Drosophila embryonic development
The rate of cell division and differentiation must be tightly regulated to ensure that an organism develops to its appropriate size and shape. The mechanisms determining the timing of cell division and differentiation are central to development, yet their control remains poorly understood. The last years have seen rapid advances in our understanding of the molecular interactions controlling embryonic development and the cell cycle. Yet, despite this detailed knowledge of molecular networks fundamental questions remain unanswered: How are growth and division coupled in cells, embryos or tissues? What ensures that cells time division and differentiation precisely during development? Which molecular mechanisms operate in embryos to ensure robust and reproducible development in face of noise in molecular and cellular processes?
We believe that the answers to these questions will ultimately require quantitative methodology and analysis. Therefore, building on previous work on the molecular mechanisms that control development and on the rapid evolving technologies enabling to probe and perturb biological systems, we pursue quantitative investigations of developmental biology along two primary axes. We study the mechanisms controlling the precise timing and number of cell divisions during embryonic and tissue development; we investigate how information is transferred across signal transduction pathways acting as morphogens. Experimentally, we combine a wide range of techniques including live imaging, quantitative image and data analysis, mathematical modeling, dynamical systems theory, genetics, molecular cell biology and embryology.
Our favorite model system is the Drosophila embryo. The Drosophila embryo has been pivotal in the identification of molecular networks controlling development and has revealed mechanisms common to most multi-cellular organisms and relevant to the basic understanding of many diseases (e.g. cancer). It is likely to play in the future an essential role in the systems level understanding of the principles by which genetic networks control cell behaviors during development. We also plan to interact with the great community of developmental biologists across campus to pursue quantitative investigations of Developmental Biology in other model systems (e.g. Zebrafish, Mouse).
Developmental control of the cell cycle
In most metazoans, early embryonic development is characterized by rapid cleavage divisions, which are followed by the morphogenetic process of gastrulation. During these stages, the cell cycle must be precisely and rapidly reprogrammed to ensure that the process of cell division is compatible with co-occurring differentiation and morphogenesis. We have developed novel molecular markers and imaging methods to study cell cycle control during early Drosophila development and are using and expanding this quantitative methodology to dissect the molecular mechanisms ensuring the precise temporal control of cell division in response to developmental inputs. The Drosophila embryo develops as a syncytium, in which nuclei invariably undergo 13 rapid divisions prior to a pause in the cell cycle coinciding with activation of zygotic gene expression and degradation of maternal product at the maternal-to-zygotic transition (MZT). The number of divisions preceding the MZT is regulated by the ratio of DNA and cytoplasmic contents (N/C ratio) by a poorly understood mechanism. Following the MZT, morphogenesis begins and cells divide again in a highly stereotypical pattern (controlled by transcription of a single rate limiting activator: cdc25string), which exemplifies the extraordinary spatiotemporal precision by which cell divisions are controlled during embryonic development. We are studying these processes by addressing the following questions: what ensures that the correct fixed number of cell divisions precedes the maternal-to-zygotic transition (MZT)? How do embryos measure the N/C ratio? How does sensing of the N/C ratio signal to the cell cycle machinery? How is cdc25string transcription controlled to ensure the correct spatiotemporal pattern of cell divisions? Are there general strategies to obtain precise temporal control of gene expression during embryonic development? Are there post-transcriptional feedback mechanisms delaying or accelerating mitosis in response to morphogenetic clues? We believe that these experiments will reveal important principles of the control mechanisms regulating development. In the long term, we intend to extend this work to the analysis of size regulation in growing tissues, using imaginal discs as model systems.
Information processing properties of signaling systems acting as morphogens
In our cell cycle work, we have shown how cells can use kinase/phosphatase cycles to average biochemical signals over time. We are currently investigating if temporal averaging through the activity of opposed enzymes might be a general principle for the precise control of biological signals. To this end, we are performing quantitative analysis of signal transduction systems beyond cell cycle control. In particular, we are focusing on signaling systems acting as morphogens during embryonic development (TGF-b and Wnt). We are developing novel molecular markers that will allow us to quantitatively measure the dynamics of these signal transduction pathways with the goal of determining their information processing properties.
Tornini VA, Puliafito A, Slota LA, Thompson JD, Nachtrab G, Kaushik AL, Kapsimali M, Primo L, Di Talia S, Poss KD. (2016) Live Monitoring of Blastemal Cell Contributions during Appendage Regeneration. Curr Biol. 21;26(22):2981-2991.
Di Talia S, Poss KD. (2016) Monitoring Tissue Regeneration at Single-Cell Resolution. Cell Stem Cell. 6;19(4):428-431.
Momen-Roknabadi A, Di Talia S, Wieschaus E. (2016) Transcriptional Timers Regulating Mitosis in Early Drosophila Embryos. Cell Rep. 13;16(11):2793-801.
Deneke VE, Melbinger A, Vergassola M, Di Talia S. (2016) Waves of Cdk1 Activity in S Phase Synchronize the Cell Cycle in Drosophila Embryos. Dev Cell. 22;38(4):399-412. doi: 10.1016/j.devcel.2016.07.023.
Chen CH, Puliafito A, Cox BD, Primo L, Fang Y, Di Talia S, Poss KD. (2016) Multicolor Cell Barcoding Technology for Long-Term Surveillance of Epithelial Regeneration in Zebrafish. Dev Cell. 21;36(6):668-80.
Ferree PL, Deneke VE, Di Talia S. (2016) Measuring time during early embryonic development. Semin Cell Dev Biol. 55:80-8.
Xenopoulos P, Kang M, Puliafito A, Di Talia S, Hadjantonakis AK. (2015) Heterogeneities in Nanog Expression Drive Stable Commitment to Pluripotency in the Mouse Blastocyst. Cell Rep. 4 pii: S2211-1247(15)00138-2.
Di Talia S, Wieschaus EF. (2014) Simple biochemical pathways far from steady state can provide switchlike and integrated responses. Biophys J. 5;107(3):L1-4.
Schrode, N., Saiz, N., Di Talia, S., and Hadjantonakis, A.K. (2014) GATA6 Levels Mondulate Primitive Endoderm Cell Fate Choice and Timing in the Mouse Blastocyst. Dev Cell 29:454-467
Di Talia, S., R. She, S. A. Blythe, X. Lu, and E. F. Wieschaus (2013) Post-translational control of Cdc25 degradation terminates Drosophila's early cell cycle program. Curr Biology 23:127-132.