Homeobox Genes and Evolution

1. Homeobox Genes and Evolution Lecture 3

2. 3’ Gene A Gene B Gene C Gene D 5’ Hox Gene Function

3. 3’ Which phenotype would you predict from loss of Gene D function? Gene A Gene B Gene C Gene D 5’

4. Which phenotype would you predict from loss of Gene D function? A B C D

5. Hox Gene Function 3’ Gene A Gene B Gene C Gene D 5’

6. Which phenotype would you predict from loss of Gene D function? 3’ Gene A Gene B Gene C Gene D 5’

7. Which phenotype would you predict from loss of Gene B function? 3’ Gene A Gene B Gene C Gene D 5’

8. Which phenotype would you predict from loss of Gene B function? A B C D

9. Hox Gene Function 3’ Gene A Gene B Gene C Gene D 5’

10. Which phenotype would you predict from loss of Gene B function? 3’ Gene A Gene B Gene C Gene D 5’

11. 3’-A-B-C-D-E-5’ 3’-C-A-E-B-D-5’ 3’-B-D-E-A-C-5’ 3’-D-B-E-A-C-5’ What order would you expect the Hox genes to be in on the chromosome? Gene D Gene B Gene E Gene A Gene C

12. Mutations in Hox genes can lead to what type of phenotype? • The anterior portion of the embryo does not develop • Several adjacent segments will be missing in an otherwise intact embryo • The affected segment will develop like its posterior neighbour • Duplication of a segment

13. Which statements describe the phenotype of the Hox mutant? • Anterior segments have been transformed into posterior ones • Abdominal segments develop as thoracic segments • Posterior segments have been transformed into anterior ones • An example of a homeotic transformation mutant

14. Which gene is predicted to control the development of the most anterior structures? A 5’ B C D 3’

15. The Antennapedia Mutation Antennapedia mutation Wild-type

16. Why do Antennapedia (Antp) mutants have legs where their antennae should be? • Absence of Antp gene function in the head transforms that segment’s appendage into one normally found in the thorax • Antp is needed for normal antennae development and is missing in these mutants • The mutants misexpress Antp in the head, transforming that segment’s appendage into one normally found in the thorax • They have no head

17. How to get legless The vertebrae of snakes show homeosis Pythons have >300 vertebrae Very few cervical (no ribs) vertebrae: lost to form thoracic (rib bearing) vertebrae Whole body resembles thorax No forelimbs Greatly reduced hindlimbs

18. Evolution of modern snakes

19. Hox gene expression boundaries correlate with morphological boundaries

20. Python thoracic TAIL HEAD limb Changes in body plan correlate with changes in Hox expression Chicken thoracic cervical lumbar TAIL HEAD HoxC6 HoxC8 limb limb What do you predict the pattern of HoxC6 and HoxC8 look like in python embryo?

21. What do you predict the pattern of HoxC6 and HoxC8 look like in python embryo? • Same as the chicken • HoxC6/C8 are not expressed in python • HoxC6/C8 expression is expanded anteriorly and posteriorly • HoxC6/C8 expression is expanded anteriorly

22. Changes in body plan correlate with changes in Hox expression Chicken Expansion of Hox expression domains creates thoracic, rib-bearing vertebrae along almost entire body length Also results in loss of forelimb, through expansion of expression into anterior somites thoracic cervical lumbar TAIL HEAD HoxC6 HoxC8 limb limb Python thoracic TAIL HEAD HoxC6 HoxC8 limb

23. Role of Hox genes in evolution 1. Most, if not all, bilaterally symmetric animals, possess one or more Hox clusters that are arranged co-linear with their head to tail expression domains 2. The Hox cluster functions during development to determine head to tail organisation by controlling region specific gene expression 3. Changes in Hox gene expression can be correlated with changes in head to tail organisation 4. New body designs DO NOT require new genes, rather the modification of the function of existing ones

24. Role of Hox genes in evolution 1. Most, if not all, bilaterally symmetric animals, possess one or more Hox clusters that are arranged co-linear with their head to tail expression domains 2. The Hox cluster functions during development to determine head to tail organisation by controlling region specific gene expression 3. Changes in Hox gene expression can be correlated with changes in head to tail organisation 4. New body designs DO NOT require new genes, rather the modification of the function of existing ones

25. Role of Hox genes in evolution 1. Most, if not all, bilaterally symmetric animals, possess one or more Hox clusters that are arranged co-linear with their head to tail expression domains 2. The Hox cluster functions during development to determine head to tail organisation by controlling region specific gene expression 3. Changes in Hox gene expression can be correlated with changes in head to tail organisation 4. New body designs DO NOT require new genes, rather the modification of the function of existing ones

26. Role of Hox genes in evolution 1. Most, if not all, bilaterally symmetric animals, possess one or more Hox clusters that are arranged co-linear with their head to tail expression domains 2. The Hox cluster functions during development to determine head to tail organisation by controlling region specific gene expression 3. Changes in Hox gene expression can be correlated with changes in head to tail organisation 4. New body designs DO NOT require new genes, rather the modification of the function of existing ones