The Homeobox (Hox) family consists of a large number of transcription factors stemming from the original isolated gene antennapedia (More? Antennapedia).
Scanning electron micrograph of wildtype and antennapedia mutant fly heads (Images Dr. Rudi Turner)
Hox appears to have a major role in determining patterns within the embryo, particularly the anterior/posterior and rostro/caudal axis. (More? see Swiss-Protein Entries). Hox proteins share a highly conserved 60 amino-acid region (More? homeodomain), which allows DNA binding which then modulates the expression of multiple target genes. It is thought that regions outside this DNA binding region may also affect specificity.Page Links: Introduction | Some Recent Findings | Homeodomains | Database Entry Links | Signaling Factors | WWW Links | References | Glossary
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Dr. Rudi Turner provided the scanning electron microscope photographs. Scanning electron microscopy of Drosophila melanogaster embryogenesis. III. Formation of the head and caudal segments. Turner, F.R. and Mahowald, A.P. (1979) Dev. Biol. 68: 96-109 |
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These are reduced size images from the Interactive Fly Page clicking image will connect with the original page. |
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This is the classic mutation that gave rise to the discovery of Hox genes and other genes related to body pattern formation. In this mutant during development the fly embryo incorrectly positioned where antenna should have be, two legs (pedia). The discovery of this mutant opened up the field of developmental genes and has recently been recognised by the 1995 Nobel prize in Medicine. Award Details LEWIS, EDWARD B., U.S.A., California Institute of Technology, Pasadena, CA, U.S.A., * 1918; NÜSSLEIN-VOLHARD, CHRISTIANE, Germany, Max-Planck-Institut für Entwicklungsbiologie, Tübingen, Germany, *1942; and WIESCHAUS, ERIC F., U.S.A., Princeton University, Princeton, NJ, U.S.A., * 1947: "for their discoveries concerning the genetic control of early embryonic development" WWW For details about other Nobel awards in Medicine see Nobel Prize Homepage which has a searchable database and an annual table of awards. |
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The 60 amino acid DNA-binding domain within the Hox protein.
There is also a good external www site called the Hox Database that is very useful if you are interested in this family of proteins.
Fruitfly Antennapedia (internet SWISS-PROTEIN)
Single letter AA code
RKRG RQTYTRYQTL ELEKEFHFNR YLTRRRRIEI AHALCLTERQ IKIWFQNRRM KWKKEN
Three letter AA code
Arg Lys Arg Gly Arg Gln Thr Tyr Thr Arg Tyr Gln Thr Leu Glu Leu Glu Lys Glu Phe His Phe Asn Arg Tyr Leu Thr Arg Arg Arg Arg Ile Glu Ile Ala His Ala Leu Cys Leu Thr Glu Arg Gln Ile Lys Ile Trp Phe Gln Asn Arg Arg Met Lys Trp Lys Lys Glu Asn
Human HoxA7 Human
Single letter AA code
R KRGRQTYTRY QTLELEKEFH FNRYLTRRRR IEIAHALCLT ERQIKIWFQNRRMKWKKEH
Three letter AA code
Arg Lys Arg Gly Arg Gln Thr Tyr Thr Arg Tyr Gln Thr Leu Glu Leu Glu Lys Glu Phe His Phe Asn Arg Tyr Leu Thr Arg Arg Arg Arg Ile Glu Ile Ala His Ala Leu Cys Leu Thr Glu Arg Gln Ile Lys Ile Trp Phe Gln Asn Arg Arg Met Lys Trp Lys Lys Glu His
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Signaling during development, though complex, can also be grouped into a few specific classes. These mechanisms have also been listed and described briefly on Signaling Mechanisms Introduction page.
Links: Journals | Online Textbooks | Search Textbooks | PubMed | Search PubMed | Glossary
Developmental Dynamics
Journal of Neurobiology
Molecular Biology of the Cell (4th Edn) Alberts, Bruce; Johnson, Alexander; Lewis, Julian; Raff, Martin; Roberts, Keith; Walter, Peter. New York: Garland Publishing; 2002.
Developmental Biology (6th Edn) Gilbert, Scott F. Sunderland (MA): Sinauer Associates, Inc.; c2000.
Search NLM Online Textbooks- "hox" : Molecular Biology of the Cell | Molecular Cell Biology | The Cell- A molecular Approach
Reviews
Articles
Search PubMed
Search Aug2005 "hox" ?? reference articles of which ?? were reviews.
Search PubMed: term= hox
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Note the dynamic developmental nature of the Internet means that some links may not always work (search using the link term).
antisense- a sequence of DNA that is complementary usually to coding sequence of DNA or mRNA. Has been used experimentally to perturb or block gene expression. Also a mechanism that has been found to occur naturally as a regulatory mechanism.
autosomal inheritance- some hereditary diseases are described as autosomal which means that the disease is due to a DNA error in one of the 22 pairs that are not sex chromosomes. Both boys and girls can then inherit this error. If the error is in a sex chromosome, the inheritance is said to be sex-linked.
base- another term for nucleotide (usually a t c g).
base pair- Double stranded DNA has nucleotides A-T, C-G, paired by hydrogen bonds (2 for AT, 3 for GC). Note this means that GC is harder to separate that AT.
DNA- DeoxyriboNucleic Acid. The genetic material found in mammalian chromosomes and mitochondria. Consisting of 4 nucleic acids (ATCG) that combine in a triptych (3 nucleotide) code for protein amino acids (3nt=1aa).
DNA duplex- double stranded base-paired DNA forming a helix.
dominant inheritance-With autosomal dominant inheritance, there is an error in one of the 22 chromosome pairs. But the damaged gene dominates over the normal gene received from the other parent. If one of the parents has a disease caused by an autosomal dominant gene, all the children will have a 50 per cent risk of inheriting the dominant gene and a 50 per cent chance of not inheriting it. The children who do not inherit the damaged dominant gene will not themselves suffer from the disease, nor will they be able to pass the gene on to future children. This type of inheritance is present for example in Huntington's disease.
exon- a block of protein encoding sequence of DNA in a gene. Many proteins are made of several exons "stitched" or spliced together by editing out non-coding (intron) sequences.
fasta- a format for listing DNA sequence, where the first line has descritive information followed on the next line by the sequence without numbering.
GC repeat- a string of GC sequence repeated several times. Also associated with GC expansion, a mutational process that may lead eventually to serious gene expression effects.
gene- a sequence of DNA that encodes an individual protein.
genetic code- the 3 nucleotide sequence that forms a codon for a single amino acid or stop. See the gene code.
genome- the complete genetic information in the form of DNA available to a specific species.
hairpin loop- a folding of RNA generated by base pairing making a "===()" structure, the end loop and or stem of this structure can then interact with proteins or other RNA.
intron- a block of DNA within a gene not encoding a protein. Edited, spliced, out during transcription into mRNA. Originally thought not to contain any information, but more and more this appears not to be the case. Some intron sequences have been shown to regulate gene expression during development (eg c elegans, Lin 14)
mRNA- messenger, transcribed from DNA in the nucleus and in mitochondria. Is translated by the ribosome in the cytoplasm (or mitochondrial matrix). Intermediate step in gene expression. (DNA-> mRNA-> protein).
mutation- any process which results in the alteration of the DNA sequence. Some conservative mutations may have no effect on the final amino acid encoded.
point mutation- a change in a single nucleotide.
recessive inheritance-With autosomal recessive inheritance, the diseased individual has inherited the same gene damage from both father and mother. The damage is found on both chromosomes in the pair. But as this is not ´dominant gene damageª, neither father nor mother show any sign of disease, they are healthy carriers of the gene. We are all carriers of about five recessive genes of this type, but as spouses are seldom carriers of exactly the same damaged gene(s), all will probably go well in the next generation.
ribosome- complex of rRNA and ribosomal proteins, bind mRNA and translate it into protein.
RNA- RiboNucleic Acid. The intermediate nucleic acid involved in gene expression. It comes in 3 forms: tRNA, mRNA, rRNA.
rRNA- ribosomal, translates mRNA into protein. rRNA provides the "scaffolding" on which many ribosomal proteins are assembled as 2 subunits that themselves assemble to form a ribosome. rRNA genes are localized to the nucleolus in the nucleus, a sometimes visible region of DNA usually constantly being transcribed.
telomere- regions at the end of chromosomes. Shortening of the telomeres is thought to be associated with cellular aging. The enzyme that maintains the telomere is called telomerase. Introducing this gene into a cell can extend the cells lifespan.
transcription factor- a protein which binds to DNA activating (usually) gene expression. There are many different ways and forms that this activation can take place, but most transcription factors fall into specific classes (eg zinc fingers, helix loop helix).
tRNA- transfer, binds single amino acids acts as a "donor' for protein synthesis.
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This section of notes introduces the topic of Hox Factors which establish body patterns in multicellular organisms.
While the final animals are significantly different, the mechanisms that regulate axis formation have common molecular pathways and signals.
An excellent example is the patterning of the limb, which has been a model for axis formation.
Molecular mechanisms of development is an exciting area and requires a variety of different skills. This page introduces only a few examples and should give you a feel for the topic.
Please email Dr Mark Hill if you wish to make a comment about this current project.
Variation