Topic 8 - Establishing the Body Plan Flashcards Preview

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Flashcards in Topic 8 - Establishing the Body Plan Deck (22):

Sexual reproduction evolved around 1200 million years ago in the ancestor of modern multicellular plants, fungi and animals. What are the distinguishing characteristics of the process of sexual reproduction?

It is characterised by the fusion of male and female gametes to generate a genetically distinct offspring.


What is segmentation during development?

The subdivision of an organism during development into multiple blocks of cells that may acquire specialised functions.


The molecules that regulate development are, for the most part, proteins. They fall into four main groups, which you have already encountered. What are they?

transcription factors
signalling molecules (including secreted and cell surface molecules)
cell adhesion molecules
extracellular matrix proteins.


Why are calcium oscillations necessary for fertilisation?

Calcium oscillations cause the re-activation of meiosis, and the release of secretory vesicles to block other sperm from fusing with the oocyte.


Calcium chelators are molecules that bind and sequester calcium ions, and hence prevent their action. What would be the effect of injection of a calcium chelator into a fertilised egg?

The processes of metabolic activation and DNA synthesis would be inhibited, thereby preventing the normal development of the embryo.


What is the body plan?

The basic shape of members of an animal phylum, assumed as an organism develops; includes features such as head-to-tail arrangement, any symmetry or segmentation, and the arrangement of any limbs.


What are maternal effect genes?

Maternal genes that exert their effect in the embryo because their transcripts (mRNA) are present in the unfertilised egg. These mRNAs are translated and the resulting gene products exert their effects in the zygote and early embryo.


What is morphogenesis?

Changes in form that occur during development?


What are morphogen gradients?

Gradients of secreted protein that play a role in morphogenesis because the response generated in cells is dependent upon the concentration of morphogen protein that the cell is exposed to.


What is a blastula?

The ball of cells that is formed as a result of the cleavage divisions of the zygote. (T8P1)The ball of cells that is formed as a result of the cleavage divisions of the zygote.


What is a blastula?

The ball of cells that is formed as a result of the cleavage divisions of the zygote. (T8P1)The ball of cells that is formed as a result of the cleavage divisions of the zygote.


What types of protein mediate the cellular response to an extracellular signal?

Cell surface receptors and the components of the downstream intracellular signalling cascades, often terminating with modulation of activity of transcription factors.


What is combinatorial control In the context of gene expression?

In the context of gene expression, this refers to the fact that a combination of different transcription factors is required to assemble the RNA polymerase II complex and promote transcription.


You encountered β-catenin in your earlier studies of this module. What function does it have in relation to stem cells?

β-catenin can both promote and inhibit embryonic stem cell (ESC) self-renewal transcription factors, depending on the cellular context. (You may recall that β-catenin increases expression of c-Myc.)


What does the sperm entry point become an organising centre for?

The sperm entry point becomes an organising centre for Par proteins and Numb, which in turn regulate asymmetric cell divisions that ensure the asymmetric distribution of maternal mRNAs in daughter cells. In Xenopus the sperm entry point becomes the ventral side.


What is neurectoderm?

The part of the ectoderm that will become neural tissue.


What is neural induction?

Specification of part of the ectoderm into neurectoderm.


What is a blastopore?

A hole formed at the dorsal end of the blastula that secretes TGF-β family molecules; important for nervous system development.


Recall that the presumptive ectoderm gives rise to both the nervous system tissues and the epidermis. If neural induction is determined by factors secreted by the organiser, suggest what these factors might do.

They could promote the differentiation of ectodermal cells into nervous system cells and/or inhibit the differentiation of ectodermal cells into epidermal cells.


What is Noggin?

Protein secreted from the organiser. It inhibits differentiation of ectodermal cells into epidermal cells and therefore promotes differentiation of neurectoderm.


Give an overview of the common mechanisms used in the earliest stages of development in many organisms.

Sperm entry to the egg triggers calcium oscillations that reactivate the final stages of meiosis and define the main body axes.
Maternally-derived mRNAs, and the proteins they encode, control the early events inside the fertilised egg, often by establishing morphogen gradients that impose regional identities on the cells. These gradients can be pre-existing (as in insects) or can be formed by asymmetric cell divisions within the oocyte (vertebrates).

Cells migrate and become specified into three distinct germ layers (the endoderm, mesoderm, and ectoderm).


What is controlled by a negative feedback loop of Notch–Delta signalling?

Neural-specified cells express low levels of neurogenin, controlled by a negative feedback loop of Notch–Delta signalling. Ultimately, this feedback loop is disturbed, causing one cell to upregulate neurogenin and adopt a neuronal fate. The neighbouring cells downregulate neurogenin and adopt glial fates.