1. HOMEOBOX GENES From Drosophila melanogaster
to pathogenesis of congenital malformations in Homo sapiens
Olga Haus

2. Homeotic genes of Drosophila melanogaster (fruit fly) hom
Genes, which mutations cause
the segments of one part of the organism becoming similar
to the segments of its another part
(homeo = I become similar)

3. Homeotic mutations
Mutations, by which one developmental scheme becomes replaced by another
They cause abnormal differentiation of organs or
the development of organs
typical for adjacent segment
Dictionary of Genetics, King & Stansfield,2002

4. Homeotic transformation (mutation)
Loss of function: one homeotic gene loses its activity in a given segment, so another hom takes over the control of this segment  the development of structures characteristic for another segment
Activating: homeotic gene, activated in a segment which normally is not directed by it, takes over the control on this segment

5. HOMEOBOX GENES
I class – HOX/Hox genes – localized in complexes (clusters: A,B,C,D) (eg. HOXA9, HOXB3)
II class – non-HOX/Hox genes – localized beyond four main clusters (eg. HOX11)

6. HOMEOBOX GENES molecular architects
determine spatial localizations of the cells in different parts of the organism along anterior – posterior axis
exist in DNA of all cells, but their expression occur only in these, which are localized in the segments directed by a given gene
in a given tissue (organ) – specific constellation (configuration) of expression of different Hox genes

7. HOMEOBOX GENES molecular architects
determine spatial localizations of the cells in different parts of the organism along anterior – posterior axis
exist in DNA of all cells, but their expression occur only in these, which are localized in the segments directed by a given gene
in a given tissue (organ) – specific constellation (configuration) of expression of different Hox genes

8. HOMEOBOX GENES molecular architects
determine spatial localizations of the cells in different parts of the organism along anterior – posterior axis
exist in DNA of all cells, but their expression occur only in these, which are localized in the segments directed by a given gene
in a given tissue (organ) – specific constellation (configuration) of expression of different Hox genes

9. HOMEOBOX homeotic sequence (180 nucleotides)
decides about the specificity (function) of a gene
codes for a homeotic domain (60 aminoacids), responsible for DNA-linking
conserved in evolution process from a common ancestor of Drosophila (hom), mouse (Hox) and man (HOX)
beside homeodomain the HOX proteins of different species are different

10. HOMEOBOX homeotic sequence (180 nucleotides)
decides about the specificity (function) of a gene
codes for a homeotic domain (60 aminoacids), responsible for DNA-linking
conserved in evolution process from a common ancestor of Drosophila (hom), mouse (Hox) and man (HOX)
beside homeodomain the HOX proteins of different species are different

11. HOMEOBOX homeotic sequence (180 nucleotides)
decides about the specificity (function) of a gene
codes for a homeotic domain (60 aminoacids), responsible for DNA-linking
conserved in evolution process from a common ancestor of Drosophila (hom), mouse (Hox) and man (HOX)
beside homeodomain the HOX proteins of different species are different

12. HOMEOBOX homeotic sequence (180 nucleotides)
decides about the specificity (function) of a gene
codes for a homeotic domain (60 aminoacids), responsible for DNA-linking
conserved in evolution process from a common ancestor of Drosophila (hom), mouse (Hox) and man (HOX)
beside homeodomain the HOX proteins of different species are different

13. HOX genes in humans 38 genes
4 clusters (A,B,C,D) – the result of double duplication of the primordial 13-genes complex
gradual loss of genes during the evolution  no cluster consists of all 13 genes of primordial complex
localization - chromosomes: 2, 7, 12, 17
paralogic (orthologic) genes – localized in the same sites (loci) of different complexes

14. HOX genes in humans 38 genes
4 clusters (A,B,C,D) – the result of double duplication of the primordial 13-genes complex
gradual loss of genes during the evolution  no cluster consists of all 13 genes of primordial complex
localization - chromosomes: 2, 7, 12, 17
paralogic (orthologic) genes – localized in the same sites (loci) of different complexes

15. HOX genes in humans 38 genes
4 clusters (A,B,C,D) – the result of double duplication of the primordial 13-genes complex
gradual loss of genes during the evolution  no cluster consists of all 13 genes of primordial complex
localization - chromosomes: 2, 7, 12, 17
paralogic (orthologic) genes – localized in the same sites (loci) of different complexes

16. HOX genes in humans 38 genes
4 clusters (A,B,C,D) – the result of double duplication of the primordial 13-genes complex
gradual loss of genes during the evolution  no cluster consists of all 13 genes of primordial complex
localization - chromosomes: 2, 7, 12, 17
paralogic (orthologic) genes – localized in the same sites (loci) of different complexes

17. LINEAR ORDER OF HOX GENES of a complex (from 3’ to 5’)
REFLECTS:
the order (succession) of body regions directed by them along antero-posterior axis
the order of their activation and expression in embryo
the degree of their susceptibility to retinoid acid

19. analogical in different species of animals
LINEAR ORDER OF GENES
analogical in different species of animals
genes in the same loci of different complexes in different animal species (paralogic genes):
more similar, structurally and functionally, than successive (next) genes in a given complex
originate from a common gene ancestor
may replace each other between the species

20. Controlled homeotic mutations in mice
pathology of mice fetuses and mature individuals
comparison with a phenotype of congenital malformation in humans
search for adequate (homologic, paralogic) HOX gene in humans

21. The enigma of HOXA3
controlled HoxA3 mutation in mice (Capecchi 1994) 
malformations of cardiovascular system
a/hypo/dys-genesia of thymus, thyroid and parathyroids
anomalies of bones and cartilages
germs (buds) of these organs – in the same region of embryo

22. The enigma of HOXA3
phenotype similar to that of Di George syndrome (22q11 microdeletion) in humans
but: in 22q11 region – no HOX gene
homology HoxA3 – HOXA3 (7p15)
hypothesis: a gene localized in 22q11 modulates the function of HOXA3

23. GSCL=goosecoid-like homeobox gene
organization of structures originating from branchia arcs (bows) and pockets (part of the skull, thymus, parathyroids, heart, main arterial truncs)
locus: 22q11.2: the smallest region of deletion (critical region) of di George syndrome

24. Clinical results of homeobox gene mutations
HOX genes:
HOXA13  hand-foot-genital s. (A,D)
HOXD13  polysyndactyly (A,D)
non-HOX genes :
EMX2  schizencephaly (split brain)
MSX2  craniosynostosis

25. Congenital malformations syndromes caused by homeobox gene mutations - exceptionally rare
Causes:
1/high degree of homology between paralogic (orthologic) HOX genes from different complexes
 full (or almost full) compensation
2/lethality of mutations of non-HOX homeobox genes

26. PAX genes Paired HOX genes homeobox - 360 nucleotides
homeodomain – about 128 aminoacids
PAX 2
- optic nerve malformations or hypoplasia
- kidneys dysplasia

27. PAX PAX 3 - expression in early neurogenesis
abnormal migration of cells originating from primordial (primitive) neural tube
(+ abnormal function of N-CAM)
Waardenburg I syndrome (deafness, abnormal ocular globe, hypertelorism, pigmentation disorders)

28. PAX genes PAX 6 - aniridia (heterozygotes) anophthalmia (homozygotes)
localized near WT1 gene (11p13)
microdeletion of this region
 WAGR syndrome (aniridia+Wilms tumor)

29. HOX genes and integrins
localization of the genes in the adjacent loci of the same chromosomes
integrins genes – also paralogic
parallel evolution of these two groups of genes = joint (simultaneous) evolution of information on organism structure plan (HOX genes) with evolution of information about interactions and migrations of cells, which fill up this structure (integrins genes)

30. HOX genes and integrins
localization of genes in the adjacent loci of the same chromosomes
integrins genes – also paralogic
parallel evolution of these two groups of genes = joint (simultaneous) evolution of information on organism structure plan (HOX genes) with evolution of information about interactions and migrations of cells, which fill up this structure (integrins genes)

31. HOX genes and integrins
localization of genes in the adjacent loci of the same chromosomes
integrins genes – also paralogic
parallel evolution of these two groups of genes = simultaneous evolution of information on organism structure plan (HOX genes) with evolution of information on interactions and migrations of cells, which fill up this structure (integrins genes)

32. Homeobox genes and cancer
homeobox genes coordinate function of many genes taking part in pathogenesis of cancer
excessive or deregulated expression of homeobex genes (coding for transcription factors) – molecular basis of many cancers
some homeobox genes = cellular protooncogenes

33. Homeobox genes and cancer
homeobox genes coordinate function of many genes taking part in pathogenesis of cancer
excessive or deregulated expression of homeobex genes (coding for transcription factors) – molecular basis of many cancers
some homeobox genes = cellular protooncogenes

34. Homeobox genes and cancer
homeobox genes coordinate function of many genes taking part in pathogenesis of cancer
excessive or deregulated expression of homeobex genes (coding for transcription factors) – molecular basis of many cancers
some homeobox genes = cellular protooncogenes

35. Homeobox genes and metastases
Transplanted tissues preserve pattern of expression of homeobox genes from primary localization
Cancer metastases – analogically (pattern of homeobox gene expression of primary tumor and also normal tissue of origin).
Constellation of expression of homeobox genes is not characteristic for tissue of metastase localization

36. Homeobox genes and metastases
pattern of expression of homeobox genes = index of histological type of primary tumor ?
a role in the diagnostics of unidentified primary tumors on the basis of homeobox pattern of metastasis (when histopathological type – not known)?

37. Cancer cells
pattern of homeobox gene expression is characteristic of tissue of origin
cancers metastasize according to information given by these genes (nonrandom, „programmed” localization of metastases for a given cancer type)