We describe a Xenopus mRNA, Xrell, that is related to the avian protooncogene c-rel, the embryonic pattern gene dorsal of Drosophila, and the mammalian transcription factor NK-KcB/KBF1. The sequence of Xrell is homologous to the other rel-related proteins in the large amino-terminal region that defres this class of transcriptional regulators, but the carboxyl-terminal part of the protein is quite different. Xrell mRNA is present throughout oogenesis and during early embryogenesis at 4 x 105 transcripts per oocyte or embryo.Xrell transcripts are present in all of the dissected parts of early embryos that we have examined. They are enriched in the animal hemisphere compared to the vegetal hemisphere of oocytes and blastulae.The rel family of proteins is a group of transcriptional regulators involved in cell differentiation and development (for review, see ref. 1). The founding member of the family v-rel (2-4) is the oncogene of reticuloendotheliosis virus strain T, which causes rapid and fatal leukemia in juvenile birds (5). The cellular counterparts of v-rel have been cloned in birds (4, 6) and in mammals (7,8). The other members of the rel family are the ubiquitous mammalian transcriptional activator NF-KB/KBF1 (9-11) and dorsal, which is believed to be the morphogen whose distribution determines the state of differentiation of cells along the dorso-ventral axis of the Drosophila embryo (ref. 12; for review, see ref. 13).All members of the rel family are very similar in an amino-terminal region of about 300 amino acids. The remaining carboxyl-terminal parts vary in size and their sequences are completely divergent. An unusual feature ofthe rel family is that the activity of its members appears to be regulated post-translationally: the activity of rel-related proteins is correlated with their nuclear localization. Two wellillustrated Agt1O (19) was screened at low stringency using a randomprimed probe (20) made from the Xba I fragment of clone pTG7, which contains the complete v-rel gene (4). Hybridization and washing of filters were done as described (21).Characterization of Clones. DNA stocks were maintained in pBS and pBluescript II vectors (Stratagene). The r117 cDNA (see Results) was subcloned into M13 vectors and sequenced using the dideoxynucleotide method (22, 23) on overlapping templates generated by digestion with exonuclease III (24). Gaps in the sequence were filled using oligonucleotide primers, and the sequence was compiled using the DB programs (25). Each nucleotide was sequenced at least twice on each strand.Oocytes and Embryos. Staged oocytes (26) and embryos (27) were obtained by standard means (28,29). Embryos were reared at 230C in 1/10 MBS (29). Dissections were carried out with fine forceps in MBS or, for neurulae, in MBS containing collagenase (Sigma C-2139; ::=1 mg/ml).Analysis of RNA. RNA from embryos or dissected tissues was prepared as described (30). Northern blots were made as described (21) and washed to O.1x SSPE/0.1% SDS at 65°C (lx SSPE = 0.18 M NaCl/10 mM phosphate, p...
In mice, the Kit receptor tyrosine kinase and its ligand, Steel factor, are required for melanogenesis, hematopoesis and gametogenesis We have identified a Xenopus gene, Xkl-1 (Xenopus Kit-like-1) whose predicted protein has striking sequence identity in the catalytic domain and kinase insert to that of c-kit. Xkl-1 is expressed only in dorsal tissues such as the nervous system, notochord and somites of neurulae. Ultraviolet irradiated embryos and animal caps treated with basic FGF unexpectedly express Xkl-1, since they are considered to develop only ventral type tissues. These observations raise the hypothesis that Xkl-1 is involved in Xenopus dorsal development and that dorsal tissues inhibit the expression of Xkl-1 in ventral structures.
In situ hybridization on whole mounts and paraffin-sectioned winter flounder (Pleuronectes americanus) gill, using riboprobes specific to a skin type antifreeze protein (AFP) gene, showed a mRNA distribution associated with cells throughout the filament and the lamellae. Immunohistochemistry using antibodies for a skin-type AFP identified cells corresponding to those detected using in situ hybridization. Parallel experiments with antibodies for chloride-cell markers showed that these cells were not involved in antifreeze-protein expression. Similarly, goblet cells did not show cross-reactivity with the AFP antibodies. This general distribution suggested that pavement cells were likely involved. Reverse transcription polymerase chain reaction using gill cDNA templates and subsequent sequencing of the products confirmed the presence of skin type AFP transcripts in this tissue. Expression of a AFP in this area may act as a first line of defence against ice-crystal migration into peripheral tissues.Résumé : L'hybridation in situ de montages entiers et de coupes à la paraffine de branchies de la plie rouge (Pleuronectes americanus) au moyen de ribo-sondes spécifiques au gène de la protéine antigel (AFP) de type cutané a démontré que la répartition de l'ARNm est associée aux cellules dans tout le filament et dans les lamelles. L'immuno-histo-chimie à l'aide d'anticorps de la protéine antigel (AFP) de type cutané a reconnu des cellules correspondant à celles obtenues par hybridation in situ. Des expériences en parallèle à l'aide d'anticorps de marqueurs des cellules à chlorures ont montré que ces cellules n'ont aucun rôle à jouer dans l'expression des protéines antigel. De même, les cellules caliciformes n'ont pas de réaction croisée avec les anticorps des protéines antigel. Cette répartition générale semble indiquer que les cellules pavimenteuses ont probablement un rôle à jouer. La transcription inverse-amplification en chaîne par polymérase au moyen de matrices d'ADNc des branchies et le séquençage subséquent des produits obtenus ont confirmé la présence de transcriptions d'AFP de type cutané dans ce tissu. L'expression des protéines antigel dans cette région peut servir de barrière à la migration de cristaux de glace dans les tissus périphériques.[Traduit par la Rédaction] 119 Murray et al.
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