1. ANA 801 - DEVELOPMENTAL BIOLOGY
AND TERATOLOGY
BY
ADESEJI WASIU ADEBAYO
UMAR BUKOLA

2. OUTLINE
2
 INTRODUCTION
 GENES OF PATTERN FORMATION
 CLINICAL IMPORTANCE
 CONCLUSION
 REFERENCES

3. INTRODUCTION
3
 In simple terms, pattern formation
refers to the generation of
complex organizations of cell fates
in space and time.
 During embryogenesis,
information encoded in the
genome is translated into cell
proliferation, morphogenesis, and
early stages of differentiation.
 Embryonic pattern arises from the
spatial and temporal regulation
and coordination of these events.

4. INTRODUCTION
4
 In developmental biology, pattern formation describes
the mechanism by which initially equivalent cells in a
developing tissue in an embryo assume complex
forms and functions (Ball, 2009)
 The process of embryogenesis involves
coordinated cell fate control (Lai, 2004; Tyler and
Cameron, 2007).
 Pattern formation is genetically controlled, and often
involves each cell in a field sensing and responding to
its position along a morphogen gradient, followed by
short distance cell-to-cell communication through cell
signaling pathways to refine the initial pattern.
 In this context, a field of cells is the group of cells
whose fates are affected by responding to the same
set positional information cues. This conceptual model

5. Why Pattern Formation?
5
 The reliable development of highly complex
organisms is an intriguing and fascinating
problem. The genetic material is, as a rule, the
same in each cell of an organism. How do then
cells, under the influence of their common genes,
produce spatial patterns ?
 Development of an organism is, of course, under
genetic control but the genetic information is
usually the same in all cells.
 A crucial problem is therefore the generation of
spatial patterns that allow a different fate of some
cells in relation to others
 (Koch and Meinhardt, 1994).

6. DEFINITION OF TERMS
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 Induction is the stimulation of a cell to differentiate in
response to a stimulus produced by another cell. It is
mediated by inducer substances that diffuse from
one cell to another. It results in cell determination.
 Determination is the commitment of a cell to undergo
differentiation. It is an irreversible process but is not
accompanied by morphological changes.
 Determinants are the cytoplasmic effector molecules
that mediate determination.
 Differentiation is the variation in the pattern of
expression of a common set of genes to form cells of
diverse morphology and function.

7. 7

8. 8

9. 9

10. 10

11. Time-table of landmarks in early
human development
11
 Day 1 - cleavage
 Days 2-4 - morula; free-
floating conceptus in uterine
tube
 Days 5-6 - formation of
the blastocyst and
embryoblast;
 - implantation
 Week 2 (days 7-14)
 - formation of the
bilaminar embryo 0.1 mm
 Week 3 (days 15-20) -
formation of the trilaminar
embryo 1.0 mm
 Week 4 (days 21-28)
 Day 21 - formation of neural
tube 2.0 mm
 Day 22 - formation of the heart
 Day 23 - formation of eye and
ear rudiments
 Day 25 - formation of branchial
arches
 Day 26 - formation of upper
limb bud
 Day 28 - formation of the lower
limb bud 5.0 mm
 Weeks 5 to 9 (2nd month) - Period of
organogenesis
 Week
6 1.0
cm
 Week 9
4.0 cm

12. GENES OF PATTERN
FORMATION
12
 Every organism has a unique body pattern.
 This patterning is controlled and influenced by the
HOMEOBOX genes.
 These specify how different areas of the body
develop their individual structures, e.g. Arms, legs
etc.

13. HOMEOBOX GENE
13
 Homeotic genes are regulatory
genes that determine where
certain anatomical structures,
such as appendages, will develop
in an organism during
morphogenesis.
 The expression of homeotic
genes results in the production of
a protein (homeodomain) that
can turn on or switch off other
genes.
 This genes act as Transcription
factors.

14. HOX GENE
14
Human hox genes are
collected into homeotic
clusters.
o There are 4 homeotic
clusters, labelled A,B,C and
D,
oEach cluster is situated on
a different chromosome.
o Each homeotic cluster
consists of 13 homeotic

15. The RNA expression pattern of three mouse Hox genes in the
vertebral column of a sectioned 12.5-day-old mouse embryo:
the anterior limit of each of the expression pattern is different
Each Hox gene is expressed in a continuous block beginning at a
Specific anterior limit and running posteriorly to the end of the
developing vertebral column

16. HOX GENE
16
The four numerically corresponding genes for the four
different clusters form a paralogous group.
o The hox genes are responsible for patterning along
the antero-posterior axis.
o The genes are expressed sequentially beginning with
the paralogous group 1, which is expressed first
o The sequential genes specify different segments in
cranio-caudal sequence extending from paralogous
group 1, which specifies the most cranial structures, to
paralogous group 13, which specifies the most caudal
structures.
o Thus the first genes to be expressed specify the most
cranial structures while the last to be expressed specify
the most caudal structures. This is responsible for the
cranio-caudal sequence of development, where the
more cranial segments develop slightly before the
more caudal structures. Consequently the upper limb
develops ahead of the lower limb.

17. Clinical Correlates
17
 Mutations in genes of pattern formation leads to a
lot of clinical important congenital malformations
and anomalies
 Aniridia
 Synpolydactyly
 Axenfeld-Rieger syndrome
 Branchiootorenal syndrome
 Coloboma
 Langer mesomelic dysplasia
 Léri-Weill dyschondrosteosis
 Microphthalmia
 Mowat-Wilson syndrome
 Amelia
 Limb deformities

18. Synpolydactyly
18
Mutation in the HOX D13
gene.

19. Aniridia
19
Aniridia with PAX6 gene
mutation.

20. Axenfeld-rieger syndrome
20
mutations in one of the genes known
as PAX6, PITX2 and FOXC1.

21. REFERENCES
21
• A. J. Koch and H. Meinhardt (1994). Biological
Pattern Formation : from Basic Mechanisms to
Complex Structures. Rev. Modern Physics 66,
1481-1507
• Ball, (2009). Shapes, pp. 261–290.
• Eric C. Lai (2004). "Notch signaling: control of
cell communication and cell fate" 131 (5). pp.
965–73. doi:10.1242/dev.01074
• Melinda J. Tyler, David A. Cameron (2007).
"Cellular pattern formation during retinal
regeneration: A role for homotypic control of cell
fate acquisition". Vision Research 47 (4): 501–

22. FOR LISTENING
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