DEV2011 Lecture Notes - Lecture 11: Lateral Plate Mesoderm, Notochord, Somite
25 May 2018
School
Department
Course
Professor
Lecture 11 – Notochord and Somites
Mesodermal fates
• Chordamesoderm → notochord
o Once mesoderm is generated through gastrulation – begins to
specialise
▪ Specific regions of mesoderm generated become molecularly
and morphologically distinct
o Driven by underlying changes in gene expression
• Chorda mesoderm sits immediately beneath developing central nervous
system
o Cells become neuroectoderm → forms neural plate (~day 19)
o Neural plate → spinal chord
o Half ectoderm will become nervous tissues and rest will become
epidermis
• Chordamesoderm cells develop thick extracellular sheath and vacuole
o Vacuole critical for producing osmotic pressure → gives notochord rod
like appearance
Notochord
• Flexible rodlike structure
• In vertebrates: main longitudinal structural element (early embryo)
• As tissue: most closely related to cartilage – serves as axial skeleton of
embryo until vertebrae forms
• Later vertebrate development
o Becomes part of vertebral column
o Higher vertebrates: notochord becomes ossified in regions of forming
vertebrae: intervertebral discs
o Notochordal cells form centre of these discs – nuclei pulposi →
cushions vertebrae
• In vertebrates: notochord is only transient structure
o Lower primitive fish and chordates, notochord used for locomotion
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Notochord: flexible rodlike structure, as tissue: most closely related to cartilage serves as axial skeleton of. Specialisation of mesoderm: paraxial mesoderm, form on both sides of median line, further laterally, intermediate mesoderm forms, thin extremities of intermediate mesoderm region form lateral plate mesoderm. Somitogenesis conserved process: precise program of segmentation from cranial to caudal direction, relate to drosophila, segmentation in invertebrate, vertebrate axial skeleton and ribs under similar molecular control. Human somitogenesis embryo tail": from day 25 of human embryogenesis, 3-4 somites are formed per day, 42-44 somite pairs formed along neural tube, positioned from cranial region to. Somite fate: somites continue differential process, mature somites are separated into 3 compartments, dermatome, dermis of back, myotome, musculature of back, limbs and ribs, sclerotome, vertebrae and rib cartilage. Intermediate mesoderm: come from same tissue embryonic origin developmentally linked to urinary system, located between paraxial and lateral mesoderm, more elongated structure is urogenetial crest origin of kidneys and gonads.
