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Unformatted text preview: BICD 130 Embryos, Genes, and Development Control of sensory and motor axon projection by netrin in the worm embryo Dark blue: UNC-6 expression UNC-6: Netrin UNC-5: Component of repulsive receptor UNC-40: Component of attractive receptor Control of commissural axon projection by Slit and Robo in the fly embryo Comm: Attractive cue Slit: Repulsive cue Robo: Slit receptor Commissural axons never leave the midline in Slit mutant embryos all CNS neurons all CNS neurons Migrating epiblast cells that disperse into the blastocoel give rise to the mesoderm of the chick embryo Distinct subdivisions of the mesoderm arise at different positions relative to the neural tube Subdivisions of the Embryonic Mesoderm chordamesoderm: notochord paraxial (somitic or dorsal) mesoderm: connective tissues of the back (bone, muscle, cartilage, dermis) intermediate mesoderm: urinary system and genital ducts lateral plate mesoderm: heart, blood vessels, blood cells; lining of body cavities; non-muscle mesodermal components of limbs head mesenchyme: connective tissues and musculature of the face Fate of the notochord Provides axial integrity of early embryo Induces formation and patterning of neural tube; helps specialize sclerotome Most degenerates; remainder forms intervertebral discs Development of paraxial mesoderm segmental plate (birds); unsegmented mesoderm (mammals) somitomeres: circular whorls of cells somites: separate blocks of cells neural crest cells somite Somites form as repeating blocks of paraxial mesoderm
somitomere Cyclical expression of the chick Hairy1 gene is associated with formation of somite boundaries expression of Hairy1 Hairy1 expression is controlled by cyclical activation of the Notch signaling pathway EphrinB2 and EphA4 receptor are expressed in complementary patterns in unsegmented mesoderm as somites bud off EphA4 receptor mRNA The A/P identity of segmental plate mesoderm is determined before somitogenesis Somite differentiation commences with the commitment of cells to the sclerotome or the dermamyotome Subdivisions of somites sclerotome: chondrocytes (cartilage cells); vertebrae and ribs dermatome: mesodermal portion (dermis) of dorsal skin myotome: musculature of back, abdominal walls, and limbs The two-layered dermamyotome subdivides into the epaxial and hypaxial myotome and the dermatome Subdivisions of myotome epaxial (closest to neural tube): epaxial muscles (deep muscles of the back) hypaxial (furthest from neural tube): hypaxial (body wall) muscles, muscles of limbs and tongue Patterning of the somite by cell signaling Subdivisions of lateral plate mesoderm in the frog embryo Derivatives of lateral plate mesoderm somatic (parietal) mesoderm: associated with ectoderm splanchnic (visceral) mesoderm: associated with endoderm coelom (body cavity): pericardial (heart), pleural (thorax), and peritoneal (abdomen) cavities Comparison of mesoderm development in chick and frog embryos Formation of the chick heart from splanchnic lateral plate mesoderm
Cardiogenic mesoderm is induced by BMP and FGF signals from adjacent anterior endoderm Fusion of the endocardial primordia creates the inner lining of the heart (endocardium) Fusion of the mesocardium forms a continuous myocardium that will give rise to heart muscle Cardia bifida caused by surgical prevention of mesodermal fusion at the ventral midline Somatic lateral plate mesoderm provides the precursors to the skeletal elements of the limb Functions of the endoderm Participates in the formation of mesodermal organs (notochord, heart, blood vessels) Constructs the linings of the digestive and respiratory tubes Major derivatives of the endoderm Digestive tube: esophagus, stomach, small intestine, colon; tonsils, thyroid, thymus, parathyroid glands (pharynx); liver, pancreas, gallbladder (caudal to stomach) Respiratory tube: trachea, bronchi, alveoli of lungs ...
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- Fall '07