Very excited to hear from Dr. Barile @SCICambridge for our Department seminars @institut_curie! Looking forward to a dense talk on lineage tracing, single-cell transcriptomics and cell cycle regulation! #Blood #stemcells #hematology

Integration is the key word, as right now there are a lot of different data types that must be considered together. Fate mapping combined with time course analysis of the population size allow to tell apart the different types of divisions (symmetric and asymmetric). (1/16)

In this way it is possible to gain insights on differentiation, heterogeneity and topology. Adding cell cycle measurements is also very informative, to detail the division mechanism and the death rate. (2/16)

This general framework, applicable to many stem cell systems, finds in the haematopoietic system a perfect candidate: a lot is known about the system regulation, how it changes with ageing or other challenging conditions, and in general about its topology. (3/16)

Starting from the fate mapping of haematopoietic stem cells, the key is having a genetic label, induced at a given time. Following the induction for a sufficient amount of time, it is possible to detect the label in all cell members of the system. (4/16)

The original model (Busch 2015) have been updated with cell-cycle data, via BrdU incorporation: mice were injected at d0 and continuously exposed to BrdU in drinking water. In this way it is possible to estimate the differentiation, net loss rate and self-renewal rates. (5/16)

Comparing only two populations (HSC and MPP), more than 80% of adult HSC divisions are symmetric in nature. The biological consequences could be of three types: supply new downstream MPPs, compensate loss by cell death and expand the HSC pool. (6/16)

This data is corroborated by other labs interested in symmetric division. When analysed in the context of aging (increase of HSCs), seems likely that the flux from the HSC to MPP compartments stays constant, even if the differentiation rate tends to decrease. (7/16)

Taking the well-known heterogeneity of the HSC compartment, and the hierarchical relationship (defined on reconstitution potential) between stem and progenitor cells, the parameter estimation led to the conclusion that MPPs have a strong high-self renewal (8/16)

This is a population observation, and leads to the conclusion that in normal haematopoiesis the HSCs are almost dispensable, at least for long period of times. (9/16)

It must also be kept into account the accumulation of the label in the different compartments studied: mathematically the label retention in hierarchically organized compartments is also hierarchical: (10/16)

the downstream compartment cannot have a higher label retention than the upstream compartment. From this type of analysis, supported also by single cell transcriptomics, seems that lineage choice occurs already in MPP, so very early in the tree. (11/16)

More surprising, seems that the HSC-to-MK differentiation pathway is quantitatively very minimal, compared to more traditional pathway HSC – MPP – MK. (12/16)

Another application of this framework is comparing different fate mapping efforts, as datasets developed using different labels are now available from several labs. (13/16)

Conciliating all these models require to identify the qualitative differences between the models, e.g. labelling efficiency. Also the shift from discrete (the conventional model) to continuous populations (the current one) must be kept in consideration. (14/16)

In conclusion, this framework allows to study dynamics, topology and heterogeneity of the hematopoietic system in a quantitative fashion. (15/16)

It recapitulates qualitatively different fate mapping experiments, and yield some new information on the HSC contribution to the MPP compartment and how the MPP compartment is probably more self-renewing than the expected. (16/16)