To compare nascent somite formation in human and mouse, we utilized the recently published mouse paraxial mesoderm microarray gene expression dataset by Chal et al. as mentioned above (GEO: GSE39613) (Chal et al., 2015xDifferentiation of pluripotent stem cells to muscle fiber to model Duchenne muscular dystrophy.
http://www.cell.com/cell-reports/fulltext/S2211-1247(17)30095-5
The average length of a somite is 80 µm (Müller and O'Rahilly, 1985). The number of presomitic spaces is 4–6. It has been shown by Arey (1938, table 3) that the first somite is large (equals the second in size) in stages 9 and 10, up to 9 somites. From 10 somites to the end of stage 11, the first is generally much smaller than the second somite. Notochordal plate.
https://www.ehd.org/developmental-stages/stage10.php
Subsequently, we asked whether the dynamics of our in vitro somite derivation reflects that of in vivo somitogenesis. Due to the scarcity of somitogenesis-stage human embryos, we turned to the mouse dataset by Chal et al. as a resource for detailed dynamics of in vivo somite development.
http://www.cell.com/cell-reports/fulltext/S2211-1247(17)30095-5
Somitogenesis is the process by which somites form. Somites are bilaterally paired blocks of mesoderm that form along the anterior-posterior axis of the developing embryo in segmented animals. In vertebrates, somites give rise to skeletal muscle, cartilage, tendons, endothelial cells, and dermis.
https://en.wikipedia.org/wiki/Somitogenesis
(B and C) Expression of the aPSM/somite (B) as well as Scl, neural crest, and neural tube (C) markers by qRT-PCR shown as average ± SEM (n = 6). ∗p < 0.05, ∗∗p < 0.01, and ∗∗∗p < 0.001 to the corresponding NT controls. Data were shown as relative expression to GAPDH levels.
http://www.cell.com/cell-reports/fulltext/S2211-1247(17)30095-5
This process occurs in an anterior-to-posterior direction and in a bilateral, symmetrical manner to provide the formation of the symmetric musculature and bones of the adult body. Somites first appear on day 20 of gestation in humans, at the head-neck border and continue to form at a rate of 3-4 somite every day. In all verterbrates, the somite formation begins at the anterior embryo immediately caudal to the otic vesicle.
http://discovery.lifemapsc.com/in-vivo-development/somite/occipital-somite
Different species have different numbers of somites. For example, frogs have approximately 10, humans have 33, chicks have 50, mice have 65, and snakes have more than 300, up to about 500. Somite number is unaffected by changes in the size of the embryo through experimental procedure.
https://en.wikipedia.org/wiki/Somitogenesis
Occipital Somite. Somites are cellular masses originating from paraxial mesoderm on both sides of neural tube during embryogenesis. The process of somite formation is one of the defining characteristics of vertebrate development.
http://discovery.lifemapsc.com/in-vivo-development/somite/occipital-somite
After the 25th day 3-4 somites per day are formed thereby 9. In humans 42-44 somite pairs 9 - 13 are formed along the neural tube. These range from the cranial region up to the embryo’s tail. Several caudal somites disappear again, which is why only 35-37 somite pairs can be counted in the end. The number of the somites that are found is used to determine the embryo's age in this developmental stage. Fig. 14 - Evolution of the mesoblast.
http://www.embryology.ch/anglais/hdisqueembry/triderm07.html
READING ASSIGNMENT: Larsen Human Embryology, 3rd Edition, pp. 79-85, 102-110. SUMMARY: During the third and fourth weeks of embryonic development the mesoderm is established as the 2nd. germ layer. The mesodermal cells are organized into 4 regions: the axial mesoderm of the prechordal. plate and notochord, paraxial mesoderm, intermediate mesoderm and lateral plate mesoderm. Each of.
http://www.columbia.edu/itc/hs/medical/humandev/2004/Chapt5-Mesoderm.pdf
what is a somite in humans
In humans Somites are bilaterally paired blocks of Mesoderm. Somites are bilaterally paired blocks of mesoderm that form along the anterior-posterior axis of the developing embryo in segmented animals.