Multiple promoters and alternative splicing: Hoxa5 transcriptional complexity in the mouse embryo.
BACKGROUND
The genomic organization of Hox clusters is fundamental for the precise spatio-temporal regulation and the function of each Hox gene, and hence for correct embryo patterning. Multiple overlapping transcriptional units exist at the Hoxa5 locus reflecting the complexity of Hox clustering: a major form of 1.8 kb corresponding to the two characterized exons of the gene and polyadenylated RNA species of 5.0, 9.5 and 11.0 kb. This transcriptional intricacy raises the question of the involvement of the larger transcripts in Hox function and regulation.


RESULTS
We have undertaken the molecular characterization of the Hoxa5 larger transcripts. They initiate from two highly conserved distal promoters, one corresponding to the putative Hoxa6 promoter, and a second located nearby Hoxa7. Alternative splicing is also involved in the generation of the different transcripts. No functional polyadenylation sequence was found at the Hoxa6 locus and all larger transcripts use the polyadenylation site of the Hoxa5 gene. Some larger transcripts are potential Hoxa6/Hoxa5 bicistronic units. However, even though all transcripts could produce the genuine 270 a.a. HOXA5 protein, only the 1.8 kb form is translated into the protein, indicative of its essential role in Hoxa5 gene function. The Hoxa6 mutation disrupts the larger transcripts without major phenotypic impact on axial specification in their expression domain. However, Hoxa5-like skeletal anomalies are observed in Hoxa6 mutants and these defects can be explained by the loss of expression of the 1.8 kb transcript. Our data raise the possibility that the larger transcripts may be involved in Hoxa5 gene regulation.


CONCLUSIONS
Our observation that the Hoxa5 larger transcripts possess a developmentally-regulated expression combined to the increasing sum of data on the role of long noncoding RNAs in transcriptional regulation suggest that the Hoxa5 larger transcripts may participate in the control of Hox gene expression.
Coulombe
Yan
Y
Centre de recherche en cancérologie de l'Université Laval, Centre Hospitalier Universitaire de Québec, L'Hôtel-Dieu de Québec, Québec, Québec, Canada.
Lemieux
Margot
M
Moreau
Julie
J
Aubin
Josée
J
Joksimovic
Milan
M
Bérubé-Simard
Félix-Antoine
FA
Tabariès
Sébastien
S
Boucherat
Olivier
O
Guillou
François
F
Larochelle
Christian
C
Tuggle
Christopher K
CK
Jeannotte
Lucie
L
D017398:Alternative Splicing / Q000235:genetics*; D000818:Animals; D000831:Animals, Newborn; D001483:Base Sequence; D001842:Bone and Bones / Q000002:abnormalities / Q000473:pathology; D017124:Conserved Sequence; D021901:DNA, Intergenic / Q000235:genetics; D004622:Embryo, Mammalian / Q000002:abnormalities / Q000378:metabolism* / Q000473:pathology; D019143:Evolution, Molecular; D018507:Gene Expression Regulation, Developmental; D006579:Heterozygote; D018398:Homeodomain Proteins / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D008817:Mice, Mutant Strains; D008969:Molecular Sequence Data; D009363:Neoplasm Proteins / Q000235:genetics; D010750:Phosphoproteins / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors; D014158:Transcription, Genetic
D021901:DNA, Intergenic; D018398:Homeodomain Proteins; C059637:Hoxa5 protein, mouse; C498560:Hoxa6 protein, mouse; C492047:Hoxa7 protein, mouse; D009363:Neoplasm Proteins; D010750:Phosphoproteins; D012333:RNA, Messenger; D014157:Transcription Factors