Identification and characterisation of two runx2 homologues in zebrafish with different expression patterns.

Genome and gene duplications are considered to be the impetus to generate new genes, as the presence of multiple copies of a gene allows for paralogues to adopt novel function. After at least two rounds of genome/gene duplication, the Runt gene family consists of three members in vertebrates, instead of one in invertebrates. One of the family members, Runx2, plays a key role in the development of bone, a tissue that first occurs in vertebrates. The family has thus gained new gene function in the course of evolution. Two Runx2 genes were cloned in the vertebrate model system the zebrafish (Danio rerio). The expression patterns of the two genes differ and their kinetics differ up to four fold. In addition, splice forms exist that are novel when compared with mammals. Together, these findings comprise opportunities for selection and retention of the paralogues towards divergent and possibly new function.

TTP, a C3H zinc finger protein gene, is expressed in mouse ovarian oocytes.

The gene TTP, encoding a C3H zinc finger protein of the TIS11 family, is expressed in growing mouse oocytes. The gene is downregulated in Graafian follicles shortly before ovulation. This corresponds to a possible function in regulation of maternal mRNA translation, a function attributed to related C3H class genes in Caenorhabditis elegans, zebrafish, and Xenopus.

Zebrafish CTH1, a C3H zinc finger protein, is expressed in ovarian oocytes and embryos.

The Zfcth1 gene is, as the previously cloned carp cth1 gene, related to the mammalian TIS 11 family of primary response genes and encodes a protein with two putative CCCH zinc fingers. This report describes the RNA expression of this gene during oogenesis and early embryogenesis up to gastrulation in the zebrafish (Danio rerio). Maternal cth1 message is present in the ovary of 1-month-old fish and of adult fish in oocytes at all stages of maturation. In the youngest oocytes the message is localized in the cytoplasm all around the nucleus, in larger oocytes the message becomes restricted to the future animal pole of the embryo, and in mature oocytes the expression is sharply localized in the cortical layer under the micropyle. After ovulation the cth1 messenger spreads over the cytoplasmic cap and is distributed over the blastomeres during subsequent cleavages. In subsequent stages maternal expression of cth1 gradually disappears. From early epiboly stages onward embryonic cth1 expression is localized to the germ ring and the hypoblast cells in the central part of the embryonic shield. In the shield, cth1 expression largely overlaps with the area of gooscoid expression in the first involuting cells. In stages after 70% of epiboly cth1 expression diminishes and soon can no longer be detected in the embryo. Next to a developmental role in cell fate determination we propose a function for cth1 during oocyte maturation.

The carp homeobox gene Ovx1 shows early expression during gastrulation and subsequently in the vagal lobe, the facial lobe and the ventral telencephalon.

The homeobox gene Carp-Ovx1 shows similarity to vertebrate and invertebrate Ovx genes and to Drosophila unplugged. Its expression pattern was studied by in situ hybridization in carp embryos and juveniles. During segmentation, expression becomes gradually limited to the neural tube. In juveniles up to 9 weeks old, cells in the ventral telencephalon, the facial lobe and the vagal lobe show Ovx1 expression, confining expression to parts with chemosensory projections.

Blastomeres and cells with mesendodermal fates of carp embryos express cth1, a member of the TIS11 family of primary response genes.

The carp cth1 gene, related to the mammalian TIS11 family of primary response genes, encodes a novel fish protein with two putative CCCH zinc fingers. This report describes the RNA expression of this gene during cleavage, blastula and gastrula stages of carp embryos. Cth1 mRNA is present in all cleavage stage blastomeres as a maternal message. After the late blastula stage, the maternal expression decreases, revealing a spot of higher expression at the margin of the blastoderm of the dome stage embryo. Further decrease of the maternal message reveals a ring of cth1 expressing cells at the blastoderm margin from the stage of 40% epiboly onwards. By alpha-amanitin treatment we established that this local cth1 expression is of zygotic origin. At the onset of gastrulation the cells of the cth1 ring involute, starting with those in the shield region, and at approximately 60% epiboly the ring is fully involuted and occupies the hypoblast layer. All cth1 transcripts have disappeared at completion of epiboly. We discuss a possible role for the putative cth1 protein during cleavage and gastrulation.

Expression of Hoxb-1 during gastrulation and segmentation stages of carp (Cyprinus carpio).

This report describes the cDNA sequence and embryonic RNA expression pattern of carp Hoxb-1. Carp Hoxb-1 is a labial-like, homeobox-containing gene of the 3' end of the Hox gene cluster. The expression pattern in carp is compared to that of homologs in other vertebrates. As holds for other Hox genes, carp Hoxb-1 is expressed with highest intensity at a sharp anterior boundary, and expression fades out towards posterior. At later stages, gaps were found in the domain. The gene is expressed from late gastrulation onwards, first mainly in the hypoblast but later in all germ layers. Its most prominent expression area is rhombomere 4 (r4) of the hindbrain. Transcripts were also found in the neural tube, mesoderm (lateral, head and presomite), epidermis and neural crest. At 30 hours post fertilization, Hoxb-1 was still expressed in r4, in the anterior trunk neural tube and in the branchial arches posterior to r4. Hox genes are thought to be involved in the specification of positional values along the embryonic anterior-posterior axis, and Hoxb-1 expression in r4 is supposed to be important for specifying the unique identity of this hindbrain segment. The conserved expression in r4 suggests that this is also true for carp Hoxb-1.

Isolation of carp cDNA clones, representing developmentally-regulated genes, using a subtractive-hybridization strategy.

A subtractive-hybridization technique, combined with differential screenings and subsequent whole mount in situ hybridization (ISH) reactions, was used to isolate novel cDNA clones representing developmentally-regulated genes of carp. Small-scale differential screenings of an oocyte and a segmentation-stage cDNA library using oocyte-specific and segmentation stage-specific enriched probes, yielded 75 positive clones. ISH screening showed that 65% (15) of the oocyte-stage clones and 50% (26) of the segmentation-stage clones were indeed stage-specific. Partial sequence analysis suggests that approximately 65% of the 41 stage-specific clones represent novel genes. In addition, an Otxl clone was isolated. Two novel clones and the Otxl clone are of special interest for developmental studies. The clones represent genes that are locally expressed during embryonic development. The expression patterns of Otxl and one of the novel clones suggest functions in specification of the anterior-posterior axis. The three clones provide molecular markers for the study of gastrulation and the patterning of the a-p axis in teleosts.

Characterization of a polymorphism in the 3' part of the chicken vitellogenin gene.

An allele giving rise to a polymorphism within the 3' part of the chicken vitellogenin gene was cloned, sequenced, and compared to the previously cloned allele. The polymorphism is formed by a perfect copy of 343 bp from intron 32 in tandem array with a perfect copy of 244 bp from intron 33; this 587-bp element is inserted in a head-to-tail arrangement in intron 33. We propose a mechanism in which an unequal crossing-over resulted in a vitellogenin gene with two exons 33, one of which was subsequently deleted. Thus, intron 33 was enlarged by the tandem repeats without affecting the protein-encoding sequence of the gene. At the boundaries of the repeated elements, two short direct repeats are found that resemble the recombination signals of immunoglobulin genes. They may have had a key role in the formation of the new allele.

Nucleotide sequence of a chicken vitellogenin gene and derived amino acid sequence of the encoded yolk precursor protein.

The gene encoding the major vitellogenin from chicken has been completely sequenced and its exon-intron organization has been established. The gene is 20,342 base-pairs long and contains 35 exons with a combined length of 5787 base-pairs. They encode the 1850-amino acid pre-peptide of vitellogenin, which is the precursor of the mature yolk proteins, the serine-rich and heavily phosphorylated phosvitin and the lipovitellin. The 217-amino acid phosvitin polypeptide occupies an internal position (residue 1112 through 1328) within the vitellogenin molecule. The 125,000 and 30,000 Mr lipovitellin polypeptides are encoded by the sequences at the N-terminal and the C-terminal sides of the phosvitin section, respectively. The main features of the gene and protein sequences, and the evolutionary implications, are discussed.

A new repetitive element of the CR1 family downstream of the chicken vitellogenin gene.

We have analyzed a repetitive DNA sequence found in the 3'-flanking region of the chicken vitellogenin gene. By its sequence, the repetitive DNA has been identified as a hitherto unreported member of the chicken CR1 family of repetitive elements. The CR1 sequence displays the structural characteristics of a long terminal repeat located at the 3' end of an avian retrovirus. The CR1 element lies 2.2 kb downstream of the vitellogenin gene and 'points' away from the gene rather than toward it. In this respect, this element differs from other CR1 repeats. The CR1 element is embedded in a region showing changes in chromatin structure implying a potential role for this sequence in determining the structural state of the local chromatin.

Conserved sequence motifs upstream from the co-ordinately expressed vitellogenin and apoVLDLII genes of chicken.

The vitellogenin and apoVLDLII yolk protein genes of chicken are transcribed in the liver upon estrogenization. To get information on putative regulatory elements, we compared more than 2 kb of their 5' flanking DNA sequences. Common sequence motifs were found in regions exhibiting estrogen-induced changes in chromatin structure. Stretches of alternating pyrimidines and purines of about 30-nucleotides long are present at roughly similar positions. A distinct box of sequence homology in the chicken genes also appears to be present at a similar position in front of the vitellogenin genes of Xenopus laevis, but is absent from the estrogen-responsive egg-white protein genes expressed in the oviduct. In front of the vitellogenin (position -595) and the VLDLII gene (position -548), a DNA element of about 300 base-pairs was found, which possesses structural characteristics of a mobile genetic element and bears homology to the transposon-like Vi element of Xenopus laevis.

Lysophospholipase activity in cell-wall fragments contaminating mitochondrial fractions of Neurospora crassa.

Crude mitochondrial preparations from Neurospora crassa contain high levels of lysophospholipase (EC 3.1.1.5) activity when assayed with lysophosphatidylcholine as a substrate. In mitochondria purified by centrifugation on a sucrose-density gradient this activity is virtually absent. The enzyme was shown to be linked to a contaminating cell fraction which mainly consists of cell-wall material as was demonstrated by electron microscopy and chemical analysis. The enzyme has no absolute Ca2+ requirement but it is slightly stimulated by 10 mM CaCl2. The pH optimum is 5.8 in presence of CaCl2 and is shifted to 4.2 when EDTA is present. In contrast to other lysophospholipases this enzyme is only slightly inhibited by deoxycholate. This detergent is able to release part of the lysophospholipase activity from the wall fragments without producing an increase in specific activity. The enzyme is possibly secreted by the cells as high lysophospholipase activities were also found in the culture medium.