Isolation and expression of homeobox genes from the embryonic chicken eye.
OBJECTIVE
To identify homeobox-containing genes that may play a role in the differentiation of ocular tissues.


METHODS
Total RNA was isolated from microdissected chicken embryo eye tissues at 3.5 days of development (embryonic day 3.5; E3.5). An "anchor-oligo-dT primer" was used for the synthesis of cDNA. Degenerate oligonucleotides designed from highly-conserved sequences in the third helix of the homeobox and the "anchor-primer" were used to amplify cDNAs by polymerase chain reaction (PCR). PCR products were cloned and sequenced. The spatial and temporal expression of selected transcripts was mapped by whole-mount in situ hybridization and northern blot analysis.


RESULTS
After sequencing eighteen clones we identified a member of the distal-less family (dlx-3) in cDNA from presumptive neural retina and three chicken homologs of the Xenopus "anterior neural fold" (Xanf-1) in cDNA from anterior eye tissue. Dlx transcripts were mapped by in situ hybridization. Expression began at Hamburger and Hamilton stage 14 (E2.5) and was widely distributed in embryonic mesenchyme on E3 and E4. Expression increased in the retina during early development and persisted until after hatching. The one anf clone selected for further study was not detected by in situ or northern blot analysis.


CONCLUSIONS
It is feasible to isolate homeobox cDNAs directly from microdissected embryonic tissues. Chicken dlx-3 mRNA has a wider distribution in the embryo than expected, based on the expression of the mouse homolog. Dlx-3 may play a role in establishing or maintaining the differentiation of the retina.
Dhawan
R R
RR
Department of Anatomy and Cell Biology, Uniformed Services University of the Health Sciences, Bethesda, MD, USA.
Schoen
T J
TJ
Beebe
D C
DC
D000595:Amino Acid Sequence; D000818:Animals; D015152:Blotting, Northern; D001934:Branchial Region / Q000378:metabolism; D002642:Chick Embryo; D004330:Drosophila; D005123:Eye / Q000196:embryology* / Q000378:metabolism*; D005801:Genes, Homeobox / Q000235:genetics*; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D017403:In Situ Hybridization; D018878:Limb Buds / Q000378:metabolism; D008648:Mesoderm / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D016548:Prosencephalon / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D012160:Retina / Q000378:metabolism; D012455:Salamandridae; D017421:Sequence Analysis; D013997:Time Factors; D014018:Tissue Distribution; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D029867:Xenopus Proteins; D015027:Zebrafish
C088334:Distal-less homeobox proteins; C098129:HESX1 protein, Xenopus; D018398:Homeodomain Proteins; D012333:RNA, Messenger; D014157:Transcription Factors; D029867:Xenopus Proteins