Gastrulation to Neurulation 1 Flashcards

1
Q

define gastrulation

A
  • rearrangement of cells by migration and division resulting in the formation of 3 embryonic germ layers: ectoderm, mesoderm and endoderm
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2
Q

what are triploblasts?

A

organisms whose body is derived from all 3 germ layers
- all triploblasts gastrulate

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3
Q

what are the 3 mechanisms of internalisation?

A

invagination - a sheet of cells bends inwards
inregression - individual cells leave sheet and become freely mesenchyme
involution - epithelial sheet rolls inwards into deeper regions of embryo to form underlying layer (happens in frog and fish)

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4
Q

what is internalisation in gastrulation and why is it important?

A
  • involves inward movement/migration of cells from surface layer of an embryo towards its interior
  • crucial for the formation of the 3 germs layers and subsequent rise to various tissues, organs, body structures in developing embryo
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5
Q

describe gastrulation in xenopus

A
  • gastrulation begins at blastopore/organizer (invagination of blastopore)
    cells involute through blastopore - endoderm rolls in, followed by mesoderm and ends up under ectoderm
  • some mesoderm and endoderm moves through ventral lip
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6
Q

what 2 mechanisms of internalisation (getting the mesoderm and endoderm inside) are involved in the xenopus

A
  • involution and invagination
  • initially invagination to form blastopore
  • involution of mesoderm and endoderm which causes movement of sheet of cells to move inside embryo by rolling under itself (i.e. mesoderm and endoderm rolling under ectoderm)
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7
Q

describe the blastopore formation in the xenopus

A
  • via invagination
  • cells constrict on apical side, epithelial sheet bends
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8
Q

what is extension convergence?

A
  • specific type of morphogenic movement
  • cells from the dorsal lip of the blastopore move inward and extend along the embryo’s head-to-tail axis while maintaining their connections with neighboring cells
  • As a result, the tissue becomes longer and narrower.
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9
Q

describe the role of the blastopore in frog/xenopus gastrulation

A
  • gastrulation movements start at the blastopore - the “Organiser”
  • signalling centre directing development of whole embryo
  • located on side of embryo where body is going to develop
  • organises antero-posterior and dorso-ventral axis
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10
Q

describe gastrulation in the zebrafish

A

EPIBOLY - cells on blastula surface divide and spread, covering yolk cell, results in thinning and expansion of blastula
INVOLUTION - organiser at one end of blastula invaginate, this initiates formation of the 3 germ layers
CONVERGENCE & EXTENSION - as involution occurs, cells from surrounding regions converge towards invaginating cells. Simultaneously, converging cells extend along anterior-posterior axis of embryo, elongating and narrowing overall shape
GERM LAYER FORMATION - invaginating cells give rise to mesoderm and endoderm layers, while outer layer forms ectoderm - they’ll all develop into different tissues and organs of zebrafish’s body

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11
Q

what is epiboly?

A

morphogenetic movement of cells sliding or expanding over another layer of cells or substrate

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12
Q

gastrulation begins with what in the chick embryo?

A
  • formation of the primitive streak - a furrow through which cells migrate
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13
Q

human embryos gastrulate like which embryos?

A

chick embryos

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14
Q

describe gastrulation in a chick

A

FORMATION OF PRIMITIVE STREAK (PS) - epiblast forms disc-shaped layer on top of yolk-sac, PS appears along midline of epiblast
INVAGINATION & MIGRATION: cells from epiblast migrate towards PS by invagination folding into mesoderm. As cells continue to migrate they differentiate into various types of mesodermal cells
ESTABLISHMENT OF GERM LAYERS: as invagination proceeds, remaining cells of epiblast split into 2 layers. Upper layer - ectoderm - gives rise to nervous system and skin. Lower layer - endoderm - forms lining of digestive and respiratory systems
MESODERM FORMATION: as cells move through PS they give rise to mesoderm layer which will give rise to heart, blood vessel, kidneys and reproductive organs etc.
NEURAL TUBE FORMATION - at anterior end specialised ectoderm cells form neural plate. edges of neural plate fold and fuse forming neural tube which will develop into brain and spinal cord

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15
Q

gastrulation starts in the primitive streak in what organisms?

A

chick
mouse
human

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16
Q

in the sea urchin which cells invaginate first?

A

mesoderm cells invaginate first and form mesenchyme and migrate, then endoderm invaginate