Structural analysis of the chicken hydroxyindole-O-methyltransferase gene.

Hydroxyindole-O-methyltransferase (HIOMT) catalyzes the final step of melatonin synthesis, a neurohormone involved in photoperiodism and produced specifically in the pineal gland and in the retina. In the chicken, HIOMT gene transcription appears to be controlled by a circadian oscillator located in the pineal gland. We have characterized the chicken HIOMT gene over 17 kb, including 2.9 kb of 5'-flanking sequence. The major transcript (1.6 kb) is composed of eight exons distributed over 7.5 kb of genomic DNA. A ninth alternative exon was identified 6 kb downstream of exon 8. It was found in minor transcripts in the pineal gland and in the retina. Sequence similarity between exons 8 and 9 suggests their origin by exon duplication. Due to early stop codons, inclusion of exon 9 truncates the open reading frame by up to 33%. A restriction fragment length polymorphism was detected for a BglII site in intron 8. Fluorescence hybridization localized the HIOMT gene on chicken chromosome 1q22. The 5'-flanking region contains GATTAA and TAATCC sequences that may be related to tissue-specific expression. An ATTTAAAT sequence at position -29 would play the role of a TATA box, as evidenced by electrophoretic mobility shift assay. Information obtained in this study open the way to further studies aimed at analyzing the circadian rhythm of transcription at promoter level.

The avian fli gene is specifically expressed during embryogenesis in a subset of neural crest cells giving rise to mesenchyme.

The ets-family of transcription factors is involved in the development of endothelial and hematopoietic cells. Among these genes, fliwas shown to be responsible for erythroblastomas and Ewing's sarcomas. Its involvement in Ewing's sarcoma, a putative neurectodermal tumor, as well as the in situ hybridization studies performed in mice and Xenopus suggested a role in neural crest development. We cloned quail fli cDNA in order to analyze in more detail its expression in neural crest cells, which have been extensively studied in avian species. Fli gene maps on chicken chromosome 1 to band q31->q33. Two RNAs are transcribed, most likely arising from two different promoters. The analysis of its expression in neural crest cells reveals that it is expressed rather late, when the neural crest cells reach their target. Among the various lineages derived from the crest, it is restricted to the mesenchymal one. It is maintained at later stages in the cartilage of neural crest but also of mesodermal origin. In addition, fli is expressed in several mesoderm-derived cells: endothelial cells as well as intermediate and splanchnopleural mesoderm.

Cytogenetic study of early chicken embryos: effect of naked neck gene and high ambient temperature.

High ambient temperature (> 30 C) decreases fertility of breeder hens, but this effect has been shown to be greatly reduced in females carrying the naked neck gene (Na). Sixty-four females each of the three different genotypes, Na/Na (homozygous naked neck), Na/na+ (heterozygous), and na+/na+ (normally feathered), were equally distributed in two climate control rooms with individual cages, at a constant temperature of either 22 C or 31 C. Five hundred and seventy-six embryos were examined after 16 to 18 h of incubation for karyological analyses. Abnormalities consisted of diploid-haploid and diploid-triploid chimeras. The frequency of chimeric embryos was significantly affected by dam genotype. Naked neck females showed a much lower proportion of abnormal embryos than normally feathered females whatever the temperature. The highest proportion of chimeras was observed for the na+/na+ dams maintained at 31 C. However, the effect of temperature was not generally significant.