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General Comment |
The homeotic genes, whose products serve as determinants of embryonic cell fate, are expressed in a series of different
but partially overlapping domains that extend along the anterior-posterior (A-P) axis of the embryo. The Hox genes
share a 180-bp homeo box, which encodes a 60-amino acid homeodomain that binds specifically to DNA. There are 4
Hox gene clusters: HOXA (formerly HOX1) on chromosome 7, HOXB (formerly HOX2) on chromosome 17, HOXC
(formerly HOX3) on chromosome 12, and HOXD (formerly HOX4) on chromosome 2. By sequence comparison, the
genes of each cluster are assigned to 1 of 13 groups. The order of the HOX genes along the chromosome reflects where
they are expressed along the body axis.
NCBI Summary:
This gene is a member of the Antp homeobox family and encodes a protein with a homeobox DNA-binding domain. This nuclear protein functions as a sequence-specific transcription factor that is involved in differentiation and limb development. Mutations in this gene have been associated with severe developmental defects on the anterior-posterior (a-p) limb axis. [provided by RefSeq]
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Comment |
Genes containing the evolutionarily conserved homeodomain sequence encode a family of DNA-binding transcription
factors whose functions are crucial for embryonic development in vertebrates, invertebrates and plants. Adjaye et al 2000 describe the
detection and analysis of transcripts of homeobox-containing genes present in cDNA libraries generated from human
unfertilized oocytes, single cleavage stage embryos (2-cell, 4-cell, 8-cell and blastocyst) and a 10-week old whole
fetus. Using degenerate primers derived from sequences within helix 1 and helix 3 of the highly conserved region of the
Antennapedia-class homeodomain, a 166 bp band was detected in all the cDNA libraries tested. Subcloning of the
oocyte-derived band revealed that it contained a heterogeneous group of 166 bp fragments. Sequence analysis of 40
independent clones demonstrated the presence of HOXA7, HOXD8, and HOXD1 sequences, the ubiquitously expressed
POU family member, OCT1, and HEX, a homeotic gene expressed in haematopoietic cells.
HOX genes are expressed in bovine and mouse oocytes and early embryos. Paul D et al. HOX proteins are transcription factors that play a major role in patterning the body axis of vertebrates from the gastrulation stage. While nothing has been reported so far about their roles at earlier stages, there is evidence that some HOX genes are expressed before gastrulation. The objective of this work was to study the pattern of expression of several HOX genes during oocyte maturation and early embryonic development up to the blastocyst stage. Using nested PCR, HOXD1, HOXA3, HOXD4, HOXB7, HOXB9, and HOXC9 transcripts were detected in bovine oocytes and early embryos at various frequencies depending on the stage of development. Quantitative PCR was performed on bovine oocytes and early embryos: relative expression of HOXD1, HOXA3, and HOXC9 decreased sharply after the 5-8 cell stage. HOXB9 relative expression increased between the oocyte and the morula stage. All transcripts seemed to be of maternal origin before the maternal to embryonic transition, as demonstrated by blocking transcription with a-amanitin. Reverse transcription was performed with either hexamers or oligo-dT, allowing for the determination that HOXC9 transcripts were slightly deadenylated during oocyte maturation; HOXD1, HOXA3, and HOXB9 transcripts were not, indicating that they could be translated. Hoxd1, Hoxa3, Hoxb9, and Hoxc9 expression was also detected in mouse oocytes and early embryos. A similar pattern of expression was found in the two species. In conclusion, mammalian HOX genes might be implicated in the control of oocyte maturation, the maternal-to-embryonic transition or the first steps of embryo differentiation. Mol. Reprod. Dev. 2011 Wiley-Liss, Inc.
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