Homeodomain binding proteins have one helix in DNA major groove and another helix across DNA that contacts other proteins. Fruitfly homeotic genes {homeobox gene} control head, jaws, teeth, thorax, and abdomen development and contain 180-base control regions {homeobox} that have helix-turn-helix {homeodomain} sequences, which are in many development genes. Regulatory region has 200,000 bases total.
retinoic acid
Extracellular-fluid retinoic acid controls homeotic-gene expression by binding to cell receptors and builds spinal cord, hindbrain, eye, and limbs. Low concentrations start gene expression at forebrain, and then higher concentrations start gene expression in sequence down to tail.
hormone
Thyroid hormone has similar receptors and controls gene expression.
Human Hox gene and other homeobox development genes {homeotic gene} can have sequences {homeotic series} along chromosomes. First gene is for mouth/nose, and last gene is for tail. Earliest homeobox genes were 1, 2/3, 4, 5, 6/7/8, and 9/10/11/12/13, in sequence. Fruit flies have 1, 2/3, 4, 5, 6, 7, 8, and 9/10/11/12/13. Fruit flies have non-homeobox region of DNA between 6 and 7. Chordates have 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and 13. Vertebrates have chordate-set variants on four different chromosomes.
Mammal genes {BF gene} can control gut, liver, and lungs. BF genes are similar to forkhead genes. BF-1 enlarges nasal retina and dorsal forebrain and is where neurons start dividing {germinal zone} before migrating. BF-2 enlarges ventral forebrain and temporal retina.
Mammal Emx-1 and Emx-2 genes {Emx gene} enlarge cerebrum, including corpus callosum. Fruitfly genes {empty spiracles gene} are similar.
Fruitfly genes {engrailed gene} can have homeoboxes but not be in homeotic gene sequence for body development. In most vertebrates, En-1 and En-2 genes, similar to engrailed gene, control midbrain and cerebellum growth.
Fruitfly genes {forkhead gene} can develop gut beginning and end.
Vertebrate genes {Hox gene} can be similar to fruitfly homeobox genes. If Hox genes are missing, symptoms are similar to DiGeorge congenital disease. Hox-b1, Hox-b2, Hox-b3, Hox-b4, and Hox-b5 genes enlarge hindbrain from third rhombomere down.
Genes {Lim-1 gene} can enlarge forebrain, midbrain, cerebellum, and first two or three hindbrain rhombomeres.
Genes {Otx gene} can affect brain development. Otx2 protein is for head development in embryo. After birth, it signals eye coordination.
Genes {Pax6 gene} can affect halteres balancing-wing development. Pax genes also affect eye and brain development.
Fruitfly genes {tailless gene} can develop gut beginning and end. Tailless gene enlarges forebrain, retina, and olfaction receptors.
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Date Modified: 2022.0225