Developmental Biology

1. Commitment
(Developmental Biology)
By
Mrs Sanchita Choubey
(M.Sc., PGDCR, Pursuing Ph. D)
Assistant Professor of Microbiology
Dr. D Y Patil Arts Commerce and Science College Pimpri, Pune

2.  The commitment of cells to specific
cell fates and their capacity to
differentiate into particular kinds of
cells. Positional information is
established through protein signals
that emanate from a localized source
within a cell (the initial one-cell
zygote) or within
a developmental field.

3. Modes of Specification
• There are three general
ways a cell can become
specified for a particular
fate, they are:
• Autonomous specification
• Conditional specification
• Syncytial specification
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4. Autonomous Specification
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• This type of specification results from
cell-intrinsic properties. The cell-intrinsic
properties arise from a cleavage of a cell
with asymmetrically expressed maternal
cytoplasmic determinants (proteins,
small regulatory RNAs and mRNA).
• The fate of the cell depends on factors
secreted into its cytoplasm during
cleavage.
• Autonomous specification was
demonstrated in 1887 by a French
medical student, Laurent Chabry,
working on tunicate embryos.
• This asymmetric cell division usually
occurs early in embryogenesis.

5. Example of Autonomous Specification
in Tunicates (Sea Squirt's)
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6. Autonomous specification in the early tunicate embryo.
When the four blastomere pairs of the 8-cell embryo are
dissociated, each forms structure that it would have
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7. Conditional Specification
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• This type of specification is a cell-
extrinsic process that relies on cues and
interactions between cells or from
concentration-gradients of morphogens.
• Inductive interactions between
neighboring cells is the most common
mode of tissue patterning.
• In this mechanism, one or two cells from
a group of cells with the same
developmental potential are exposed to a
signal from outside the group.

8. • Another mechanism that determines the
cell fate is regional determination.
• Regional determination is based upon the
region or position of cell within the
embryo, it is also known as positional
value.
• This was first observed in chick, when
mesoderm was taken from the
prospective thigh region of a chick
embryo, was grafted onto the wing
region and did not transform to wing
tissue, but instead into toe tissue.
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9. Example (in Sea urchin cell)
What a cell becomes depends upon its position in the embryo.
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11. Syncytial Specification
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• This type of a specification is a
hybrid of the autonomous and
conditional that occurs in insects.
This method involves the action of
morphogen gradients within the
syncytium.
• There are no cell boundaries in the
syncytium, these morphogens can
influence nuclei in a concentration-
dependent manner.

12. • Many insects also use a third means, known
as syncytial specification, to commit cells
to their fates. Here, interactions occur not
between cells, but between parts of one
cell.
• In early embryos of these insects, cell
division is not complete. Rather, the nuclei
divide within the egg cytoplasm. This
creates many nuclei in the large egg cell. A
cytoplasm that contains many nuclei is
called a syncytium.
• The egg cytoplasm, however, is not uniform.
Rather, the anterior of the egg cytoplasm is
markedly different from the posterior.
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13. Example
(in fruit fly)
Syncytial
specification in the
fruit fly Drosophila
melanogaster.
Anterior-posterior
specification
originates from
gradients within
the egg cell. Bicoid
mRNA is stabilized
in the most
anterior portion of
the egg, while
Nanos mRNA is
restricted to the
posterior portion
of the egg.
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14. • Determination is followed by
differentiation, the actual
changes in biochemistry,
structure, and function that
result in specific cell types.
• Differentiation often involves
a change in appearance as
well as function.
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15. Cell interactions
• Contact with neighboring
cells influence cell fate.
• There are three pathways
of cell interactions, these
are:
• Diffusion
• Direct contact
• Gap junction
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17. THANKS
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