16 Questions
What is the function of monoamine oxidase on the left side?
It breaks down serotonin
What is the role of PITX2 in establishing left-sidedness?
It is a transcription factor that establishes left-sidedness
What is the role of SHH in establishing left-sidedness?
It represses PITX2 expression on the right side
What is the function of NKX 3.2 in establishing right-sidedness?
It establishes expression of snail on the right lateral plate mesoderm
What is the role of Hox genes in vertebrates?
They regulate the number of body segments and appendages
What is the role of snail gene in establishing right-sidedness?
It is only expressed on the right lateral plate mesoderm
What is the primary function of the HOX genes in embryonic development?
Specifying segment identity of tissues along the cranio-caudal axis
What is the significance of the number of somites in embryo development?
Determining the age of the embryo
What is the role of the Brachyury (T) gene in embryonic development?
Establishing the middle to caudal region of the embryo
What is the consequence of the absence of the Brachyury gene?
All of the above
What is the role of FGF8 in establishing the left-right body axis?
Activating the expression of Nodal
What is the function of the PITX2 gene in embryonic development?
Controlling left-sidedness
What is the significance of the node in embryonic development?
Maintaining the node and inducing regional specificity
What is the function of the BMP4 protein in embryonic development?
Regulating the formation of the notochord
What is the consequence of the misregulation of the Brachyury gene?
All of the above
What is the role of the Hensen's node factor 3 beta (HNF3) in embryonic development?
Maintaining the node and inducing regional specificity
Study Notes
Craniocaudal Patterning
- Repeated segments governed by HOX genes, which control body plan along cranio-caudal axis (anterior-posterior) and specify segment identity of tissues within the embryo
- Age of embryo based on number of somites, which become hard to count, then determined by Crown-rump length (CRL) measured from vertex of skull to midpoint between apices of buttocks
Hensen's Node and Forebrain Formation
- Hensen's node factor 3 beta (HNF3β) maintains node and induces regional specificity in forebrain and midbrain areas
- Goosecoid, chordin, noggin, follistatin, nodal antagonize and inhibit activity of BMP4 (bone morphogenetic protein 4), which favors dorsalization and cranial mesoderm dorsalization into notochord and somites
- Nodal gene initiates formation of primitive streak, maintains PS, and regulates formation of dorsal and ventral mesoderm, as well as head and tail structures
Embryonic Disc and Mesoderm Formation
- BMP4 and FGF (Fibroblast growth factor) are secreted along embryonic disc, ventralizing mesoderm to form intermediate and lateral plate mesoderm
- Node is the organizer, homologous to chordamesoderm in dorsal lip of blastopore
- Nodal gene is homologous to goosecoid gene, coding for transcription factors regulating activity of genes at dorsal lip of blastopore and node
Left-Right Body Axis
- FGF8 secreted by node establishes expression of Nodal, which activates Lefty2 in lateral plate mesoderm
- Nodal and Lefty2 activate PITX2 gene, coding for transcription factor controlling left-sidedness
- SHH (sonic hedgehog) represses left-sided gene (PITX2) expression on the right
- 5HT (serotonin) neurotransmitter breakdown favored towards the left, activating FGF8 and regulating cascade of chain activation leading to left-sidedness
Homeobox/HOX Genes
- 4 classes of HOX genes in vertebrates (A-D), responsible for determining general body plan
- HOX genes control number of body segments, number of somites, and placement of appendages (forelimbs, hindlimbs) and animal head-tail directionality
Learn about the cranial to caudal patterning in embryonic development, including the role of somites, vertebrae, and HOX genes in controlling the body plan.
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