Homeotic genes

Welcome to the world of Homeotic genes. In this presentation I talk about the interesting history behind homeotic genes as to how it was discovered. Also, the various deformities in Drosophila related to mutations in homeotic genes and the characteristics of homeotic genes. I also talk about hox genes in humans and their function.

1. Homeotic Genes Name: Rishika Maji Course & Year: BSc. (H) Zoology 3 rd year Subject: Developmental Biology Roll no: 18/154 Exam Roll no. : 18043569010 Submitted to: Dr. Brototi Roy and Dr. Shilpa Bharti Batch: 2020-2021

2. 01 Introduction Homeotic gene , are a group of genes that control the pattern of body formation during early embryonic development of organisms. Homeotic genes codes for transcription factors that dictate the development and compartmentalization (regionalization) of body parts in animals along the anterior-posterior (head to tail) axis.  “The genetic control of the early embryonic development”. The Editors of Encyclopaedia Britannica. (2018, May 23). Homeotic gene | biology . Encyclopedia Britannica. https://www.britannica.com/science/homeotic-gene 2

3. Discovery The Role of Homeotic Genes in Development • . U. (2019, October 20). IBiology. https://www.ibiology.org/development-and-stem-cells/homeotic-genes/ 3 William Bateson (1894) Coined the term Homeosis or Homeotic (from the Greek root “for the same”) Homeotic roughly meant “Something has been changed into the likeness of the other”. Diagram of an insect given by Bateson under deformed animals Legs in place of antenna

4. Discovery djarm67. (2008, June 4). Evolution - Great Transformations 5of6 . YouTube. https://www.youtube.com/watch?v=voQQ1dhCqZg 4 2. Edward D. Lewis Studied the development of anterior posterior segment development in Drosophila melanogaster. He proposed “Each segment of the fly embryo was directed to develop by a single gene”. A group of genes like a genetic tool kit appeared to be laying out the body plan of the developing embryo Segment Development in Drosophila

5. Discovery djarm67. (2008, June 4). Evolution - Great Transformations 5of6 . YouTube. https://www.youtube.com/watch?v=voQQ1dhCqZg 5 3. Levine & McGinnis Discovered the gene antennapedia responsible for development of legs in the thorax region. Mutation in the gene results in the formation of legs from the head where the antenna grows. Fluorescence showed that the gene antennapedia responsible for the development of the thoracic segment in the fly was a band located on the thoracic region itself. Band of antennapedia gene

6. Discovery G Halder, P Callaerts, WJ Gehring, Induction of ectopic eyes by targeted expression of the eyeless gene in Drosophila ,  24 Mar 1995, https://science.sciencemag.org/content/267/5205/1788 6 4. Walter J. Gehring Isolated the gene in Drosophila that triggered the development of eye. The gene was called eyeless . Replaced this gene with the mouse eye gene. Normal Compound eyes developed in Drosophila. Shows that homeotic genes are conserved. Development of eyes from mouse gene Eyeless

7. Homeotic genes in Drosophila Lepesant, J. A. (1990). [Homeotic genes] . PubMed. https://pubmed.ncbi.nlm.nih.gov/1976313/ Hox gene a subset of homeotic genes . Embryonic expression in Drosophila detects segment identity. Also known as Selector genes as these genes “select” the identity of each segment. There are 8 major Hox genes in Drosophila, located in two large gene clusters: Antennapedia Complex Bithorax complex 4 genes: Head and the first and second thoracic segments. 3 genes: Third thoracic segment and 8 abdominal segments.

8. Homeotic genes in Drosophila SnapRevise. (2019, July 3). Gene Regulation: Hox Genes | A-level Biology | OCR, AQA, Edexcel . YouTube. https://www.youtube.com/watch?v=1Ecm8UgiXBU Hox genes expression responsible for anteroposterior development of fly embryo. Spatial linearity : Order of the genes on the chromosomes matches the expression pattern along the embryo. Temporal expression of genes stating with expression of the anterior Hox gene. 1 3 2 This phenomenon is known as co-linearity .

9. Examples of implication of Hox mutation Homeotic genes (article) . (2018, May 24). Khan Academy. https://www.khanacademy.org/science/biology/developmental-biology/sin-development/a/homeotic-genes 9 Normal Antennapedia gene expressed in second segment of a fly's thorax and helps in proper development of fly's second pair of legs and other segment-specific structures. Mutation in the form of change in location of the gene Mutation causes legs to grow from the fly's head in place of antennae 1. Antennapedia

10. Examples of implication of Hox mutation 10 Normal Ultrabithorax gene expressed strongly in the 3 rd segment of the thorax , which bears the fly's rearmost pair of legs.  Represses formation of wings in the 3 rd segment. Forms halteres instead. Mutation in the form of inactivation of the gene Mutation causes the halteres to be converted to a second set of wings, neatly positioned behind the normal set. 2. Ultrabithorax Homeotic genes (article) . (2018, May 24). Khan Academy. https://www.khanacademy.org/science/biology/developmental-biology/sin-development/a/homeotic-genes

11. Homeodomain This protein acts like a transcription factors . These binds to the DNA sequence and can regulate the activation or inactivation of genes during embryogenesis responsible for formation of segments and body parts . 11 Homeodomain : 60 amino acid protein. Forms an helix-turn-helix. Highly conserved protein in animals. SnapRevise. (2019, July 3). Gene Regulation: Hox Genes | A-level Biology | OCR, AQA, Edexcel . YouTube. https://www.youtube.com/watch?v=1Ecm8UgiXBU

12. Hox genes in humans 3/13/2021 12 Hox  genes are found in many different animal species, including mice and humans. They also tend to have the same order on the chromosome in all of these species.  The presence of similar  Hox  genes in different species reflects their common ancestry.

13. Hox genes in humans 13 In vertebrates like humans and mice,  Hox  genes now exist as four similar gene clusters labeled A through D. All these gene clusters work together just like as explained in Drosophila , along the head-tail axis.  Just like Drosophila these genes are collinear that is they show spatial linearity and temporal order of gene expression . Mutations in   HoxD13   in humans can cause a genetic condition called synpolydactyly , in which people are born with extra fingers or toes that may also be fused together. Lepesant, J. A. (1990). [Homeotic genes] . PubMed. https://pubmed.ncbi.nlm.nih.gov/1976313/

14. Conclusion 14 Homeotic genes are responsible for commonality among animals. Animals resemble each other because of the same set of genes. Everything is not as complicated as it seems to be. djarm67. (2008, June 4). Evolution - Great Transformations 5of6 . YouTube. https://www.youtube.com/watch?v=voQQ1dhCqZg