Download Patterns in Development

Patterns in Development
• Pattern formation must be established via induction prior to
morphogenesis. The pattern formation is related to the body plan
(its 3-D shape) for that specific organism. In animals pattern
formation is limited to embryos and young juveniles.
– Plants - morphogenesis and pattern formation continue throughout
the life of the plant.
– Animals - major axis are determined first(ventral/dorsal,
anterior/posterior, & right/left)
• the major axis make up the positional information
• drosophila development
– maternal effect genes(egg-polarity genes)
determine the axis of development in the
ovum
• bicoid- maternal gene responsible for establishing
the anterior portion of the embryo
– bicoid is concentrated at the anterior portion of the
egg before fertilization
– mutated bicoid results in 2tails
– Bicoid at both sides results in 2heads
• Maternal effect genes set off a cascade of embryo
segmentation-genes during development
– products are often transcription factors & signal
molecules that set off the next set of genes
– examples of segmentation-genes are
» Gap-genes - regulate pair-rule genes
» Pair-rule genes - activate segment-polarity
genes
» Segment-polarity genes - determines the
boundaries and axis
• Identity of the segments are determined by
homeotic genes
– specify the appendages that form on the individual
segments
• Plants - root/shoot axis is
determined first
– not as many model
organisms as much less
resources are dedicated to
plant research
– positional information is
more important than cell
lineage (many cells are
totipotent)
– cell-signaling (induction)
and transcription regulation
drive development
• the embryonic development
occurs inside the seed
• post embryonic
differentiation is controlled at
the apical meristem
Cell lineage
• Cell lineage is a term that describes the connection
between the differentiated cell and the cells that it came
from. Two main factors contribute to the cell lineage:
• Induction - signals between cells influence the
differentiation of nearby cells
• Apoptosis - Programmed cell death
–
–
mechanism is essential in the development of the embryo
when the signal is received the cell shrinks becomes lobed
(blebbing), the nucleus condenses and the DNA is fragmented.
Neighboring cell engulf and digest the remains.
– necessary for the development of the nervous system,
operation of the immune system, and morphogenesis of the
hands and feet
Homeobox
• Comparisons of embryos leads to clues of evolution. With modern
genomic techniques, researchers are discovering how minor
environmental pressures can lead to morphological changes in a
species. Study of many animal genomes led to the discovery of
similar sequences of developmental genes called the homeobox.
• 180 nucleotide sequence common in the homeotic genes (hox
genes) of all animals
– codes for a 60 AA sequence called the homeo domain of
developmental proteins
– similar genes are also found in eukaryotic plants and in egg polarity
genes (bicoid)
• suggests the origin is very early in the evolutionary tree