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The control of somitogenesis in mouse embryos
Abstract:
Somitogenesis in the mouse embryo commences with the generation of presumptive somitic mesoderm at the primitive streak and in the tail-bud mesenchyme. The presumptive somitic mesoderm is then organized into somite primordia in the presomitic mesoderm. These primordia undergo morphogenesis leading to the segmentation of somites at the cranial end of the presomitic mesoderm. Somite sizes at the time of segmentation vary according to the position of the somite in the body axis: the size of lumbar and sacral somites is nearly twice that of upper trunk somites and of tail somites. The size of the presomitic mesoderm, which is governed by the balance between the addition of cells at the caudal end and the removal of somites at the cranial end, changes during embryonic development. Somitogenesis is disturbed during the compensatory growth of mouse embryos which have suffered a drastic size reduction at the primitive-streak and early-organogenesis stages. The formation of somites is retarded and the upper trunk somites are formed at a smaller size. The embryo also follows an entirely different growth profile, but a normal body size is restored by the early foetal stage. The somite number is regulated to normal and this is brought about by an altered rate of somite formation and the adjustment of somite size in proportion to the whole body size. It is proposed that axis formation and somitogenesis are related morphogenetic processes and that embryonic growth controls the kinetics of somitogenesis, namely by regulating the number of cells allocated to each somite and the rate of somite formation.
Insights
Mouse embryonic development involves somitogenesis, the formation of body segments. Embryonic growth rate influences somite formation timing and size, with adjustments ensuring normal body size restoration.
Area of Science:
- Developmental biology
- Embryogenesis
- Morphogenesis
Background:
- Somitogenesis is the process of forming somites, the precursors to vertebrae and skeletal muscle.
- Somite formation occurs sequentially along the anterior-posterior axis of the developing embryo.
- Somite size varies by position, with lumbar and sacral somites larger than upper trunk and tail somites.
Purpose of the Study:
- To investigate the relationship between embryonic growth and somitogenesis in mice.
- To understand how compensatory growth affects somite formation and size.
- To explore the regulatory mechanisms controlling somite number and size during development.
Main Methods:
- Observation of mouse embryos undergoing somitogenesis.
- Analysis of somite formation and size during normal and compensatory growth.
- Correlation of embryonic growth profiles with somitogenesis kinetics.
Main Results:
- Somitogenesis is disrupted in mouse embryos with reduced size during early development.
- Retarded somite formation and smaller upper trunk somites were observed.
- Despite initial disruptions, normal body size and somite number are restored by the early fetal stage.
Conclusions:
- Embryonic growth rate is a critical factor controlling the kinetics of somitogenesis.
- Axis formation and somitogenesis are interconnected morphogenetic processes.
- The embryo regulates somite number and size in proportion to overall body size during development.