Patterns in Development

1. 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

2. 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 bicoidresults in 2tails • Bicoidat 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

3. 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

4. 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

5. 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 (hoxgenes) 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