BIOL 1911 Chapter Notes - Chapter 47.3: Bone Morphogenetic Protein 4, Asmodel, Zone Of Polarizing Activity
29 Apr 2018
School
Department
Course
Professor
47.3 – Cytoplasmic determinants and inductive signals
regulate cell fate
• Cell behavior and molecular mechanisms that underlying it are crucial to morphogenesis
• How do shared cellular and genetic processes ensure that particular types of cells each end up in the right place?
• Cells arise by division, take up particular locations in the body and become specialized in structure and function during
embryonic development
• Development fate = where a cell resides, how it appears, and what it together does
o Determination = process by which a cell or group of cells becomes committed to a particular fate
o Differentiation = resulting specialization in structure and function
• E ’ n of genes present in
’
o Exception: certain mature immune cells
• How do cells acquire different fates given the above?
o Particular tissues and cells differ from one another by expressing distinct sets of genes from their shared
genome
• Uncovering the mechanisms that direct the differences in gene expression underlying developmental fates = a major
focus of developmental biology
o One method: trace tissues and cell types back to their origins in the early embryo
Fate Mapping
• One way to trace the ancestry of embryonic cells via direct observation through the microscope
• Fate map = diagram showing the structures arising from each region of an embryo
o Vogt in the 1920s used this to determine where groups of cells from the blastula would end up in the gastrula
o Later, techniques developed that allow researchers to mark an individual blastomeres during cleavage and
follow the marker as it was distributed to all the mitotic descendants of that cell
o Researchers have determined the complete developmental history, or lineage, of every cell in C. elegans
▪ Can identify progeny of a single cell using the cell lineage diagram
o Fate-mapping in C. elegans paved the way for major discoveries about programmed cell death
▪ Gene part of the pathway is present in a wide range of animals, including humans
▪ Scientists were positioned to answer questions about underlying mechanisms such as how the basic
axes of the embryo are established, having established fate maps for early development
o Fate of germ cells (pg. 1057)
Axis Formation
• Body plan with bilateral symmetry exhibits asymmetry along the dorsal-ventral and anterior-posterior axes and
symmetry along the right-left axis
find more resources at oneclass.com
find more resources at oneclass.com
• When are these three axes established?
Axis Formation in the Frog
• Future position of the anterior-posterior axis is determined during oogenesis
o Asymmetry in the egg is apparent in the formation of two distinct hemisphere
o Dark melanin granules are embedded in the cortex of the animal hemisphere
o Yellow yolk fills the vegetal hemisphere
o Animal-vegetal asymmetry dictates where the anterior-posterior axis forms in the embryo
o Note: anterior-posterior and animal-vegetal axes are not the same; head of the embryo does not coincide with
the animal pole
• Dorsal-ventral axis of frog embryo is determined at random
o Wherever the sperm enters in the animal hemisphere determines where the dorsal-ventral axis forms
o Cortical rotation - the egg surface (plasma membrane and associated cortex) rotates with respect to the inner
cytoplasm once the sperm and egg have fused
▪ From the perspective of the animal pole, the rotation is always towards the point of sperm entry
o Resulting interactions between molecules in the vegetal cortex and in the inner cytoplasm of the animal
hemisphere activate regulatory proteins which direct expression of one set of genes in dorsal regions and
another set of genes in ventral regions
Axis Formation in Birds, Mammals, and Insects
• There are many different processes by which animal embryos establish their body axes
• Sperm appears to contribute to axis formation in mammals in a direct manner as in frogs
• Orientation of the egg and sperm nuclei before they fuse influences the location of the first cleavage plane
o In chicks, anterior-posterior axis is established by the pull of gravity during the time when the soon-to-be-laid
’
o In zebrafish, signals within the embryo gradually establish the anterior-posterior axis in over the course of a
day
o In insects, gradients of active transcription factors across the body establish both the anterior-posterior and
dorsal-ventral axes
• The position of the left-right axis is fixed once the anterior-posterior and dorsal-ventral axes are established
o Still, specific molecular mechanisms must establish which side is left and which is right
o In vertebrates, there are marked left-right differences in the location of internal organs as well as in the
organization and structure of the heart and brain
Restricting Developmental Potential
• Fertilized egg give rises to all cell fates
• Determination = commitment to a particular cell fate
• How long during development do cells retain this ability to differentiate?
• Spemann, in 1938, demonstrated that the first two blastomeres of the frog embryo are totipotent, meaning that they can
develop into all the different cell types of that species
• In mammals, embryonic cells remain totipotent through the eight-cell stage
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
In chicks, anterior-posterior axis is established by the pull of gravity during the time when the soon-to-be-laid (cid:566)(cid:568)(cid:568) (cid:570)(cid:580) (cid:581)(cid:579)(cid:562)(cid:583)(cid:566)(cid:573)(cid:570)(cid:575)(cid:568) (cid:565)(cid:576)(cid:584)(cid:575) (cid:581)(cid:569)(cid:566) (cid:569)(cid:566)(cid:575)"(cid:580) (cid:576)(cid:583)(cid:570)(cid:565)(cid:582)(cid:564)(cid:581) In zebrafish, signals within the embryo gradually establish the anterior-posterior axis in over the course of a day. In vertebrates, there are marked left-right differences in the location of internal organs as well as in the organization and structure of the heart and brain. If cells or groups of cells from a single embryo become separated before the trophoblast and inner cell mass become differentiated, two embryos grow, each with its own chorion and amnion (the case for 1/3 of identical twins) Inactivating bmp-4 allows cells on dorsal side to make dorsal structures such as notochord and neural tube. Cilia and cell fate: cilia are essential for specifying cell fates in human embryos, two types: stationary and motile cilia, both play crucial roles in development, stationary primary cilia monocilia.
