A gestational metronome: role of the placenta in the control of developmental tempo

Supervised by: Dr Alberto Rosello-Diez (ar2204@cam.ac.uk) and Prof. Amanda Sferruzzi-Perri (ans48@cam.ac.uk)

Project Title: A gestational metronome: role of the placenta in the control of developmental tempo

Project description 

Mammals differ widely in their developmental tempo, i.e. the exact time/speed at which they reach or progress through a given stage. Tight control of these processes is critical for normal development, but we lack a basic understanding of how developmental tempo is regulated and how it changes across evolution. Whereas some intrinsic factors (metabolic rate, protein stability) have been shown to play a role in vitro (1, 2), it is not clear how relevant these are in vivo, or how they interact with extrinsic factors. Regarding the latter, several studies suggest that the gestational environment dictates developmental tempo. Indeed, rat embryos require two extra days of development to reach equivalent stages to a mouse embryo, but this temporal shift can be modulated when mouse and rat tissues are combined: i) rat embryos developing inside a mouse uterus (connected to mouse placentas) develop at the higher speed of a mouse embryo (3); ii) mouse embryos developing inside a rat uterus (connected to rat placentas) develop at the slower speed of rat embryos (3); iii) rat neurons developing inside a mouse embryo forebrain accelerate their maturation, adapting to the speed of mouse neuronal development (4). We hypothesize that the placenta is a likely candidate to dictate developmental tempo in the embryo. To test this, we will characterise: placental signals and embryo responses during normal mouse and normal rat development, as well as in rat embryos developing in a mouse environment (with a mouse placenta). To generate the latter, tetraploid embryo complementation will be used, in which rat embryonic stem cells will be injected into tetraploid mouse embryos, so that a rat embryo develops supported by a mouse placenta (3). Moreover, to elucidate which placental signals may be relevant, we will use a mouse line (TurboID) in which secreted proteins produced by a tissue of interest are labelled with biotin, so that they can be identified in the embryo (5). To identify embryo responses, we will use the limb as a target organ with a very stereotypical and well-described morphogenetic temporal sequence. Specifically, we aim to:

1. Generate TurboID-expressing tetraploid embryos and inject them with mouse ESCs to confirm that conceptuses expressing TurboID exclusively in the extraembryonic tissues are generated.
2. Perform proteomic analysis of biotinylated proteins from full embryos at embryonic day (E)8.5 and E9.5, and of the limbs at E10.5. This will be done after complementation of TurboID-tetraploid-embryos with: a) mouse ESCs; b) rat ESCs. Differential analysis of these two experiments will identify a list of candidate signals that instruct tempo in the target tissues.
3. Perform single-cell RNA-sequencing analysis of the placentas from experiments 2.a) and 2.b). Expression in these datasets will be cross-referenced with the candidates from Aim 2, to refine the list of tempo-modulating signals. Future projects will functionally test these candidates.
4. Perform RNA-seq on the fetal tissues/limbs, to identify gene-expression changes that respond to the altered gestational support.

In summary, this project aims to reveal new fundamental biology, which could be relevant for the diagnosis and prevention of fetal growth restriction.

References

1. T. Rayon et al., Species-specific pace of development is associated with differences in protein stability. Science 369,  (2020).
2. M. Diaz-Cuadros et al., Metabolic regulation of species-specific developmental rates. Nature 613, 550-557 (2023).
3. T. Yamaguchi et al., An interspecies barrier to tetraploid complementation and chimera formation. Sci Rep 8, 15289 (2018).
4. J. Huang et al., Generation of rat forebrain tissues in mice. Cell 187, 2129-2142 e2117 (2024).
5. R. Yang et al., A genetic model for in vivo proximity labelling of the mammalian secretome. Open Biol 12, 220149 (2022).

Candidate background requirements

Developmental biology background and basic molecular biology skills.