Expression of dachshund in wild-type and Distal-less mutant Tribolium corroborates serial homologies in insect appendages.

We isolated the homologue of the Drosophila gene dachshund (dac) from the beetle Tribolium castaneum. Tc'dac is expressed in all appendages except urogomphi and pleuropodia. Tc'dac is also active in the head lobes, in the ventral nervous system, in the primordia of the Malpighian tubules and in bilateral stripes corresponding to the presumptive dorsal midline. Expression of Tc'dac in the labrum lends support to the interpretation that the insect labrum is derived from a metameric appendage. The legs of Tribolium accommodate two Tc'dac domains, of which the more distal one corresponds to the single dac domain described for Drosophila leg discs. In contrast to Drosophila, where this domain is thought to intercalate between the homothorax (hth) and the Distal-less (Dll) domains, in Tribolium it arises from within the Dll domain. In embryos mutant for the Tc'Dll gene we find that the distal Tc'dac domain in the legs, as well as the expression in the labrum, are deleted while the proximal leg domain and the mandibular expression are unaffected. Based on Tc'dac expression in wild-type and mutant embryos, we demonstrate serial homology of the complete mandible with the coxa of the thoracic legs, which affirms the gnathobasic nature of the insect mandible.

Double-stranded RNA interference in the spider Cupiennius salei: the role of Distal-less is evolutionarily conserved in arthropod appendage formation.

Chelicerates represent a basal arthropod group, which makes them an excellent system for the study of evolutionary processes in arthropods. To enable functional studies in chelicerates, we developed a double-stranded RNA-interference (RNAi) protocol for spiders while studying the function of the Distal-less gene. We isolated the Distal-less gene from the spider Cupiennius salei. Cs-Dll gene expression is first seen in cells of the prosomal segments before the outgrowth of the appendages. After the appendages have formed, Cs-Dll is expressed in the distal portion of the prosomal appendages, and in addition, in the labrum, in two pairs of opisthosmal (abdominal) limb buds, in the head region, and at the posterior-most end of the spider embryo. In embryos, in which Dll was silenced by RNAi, the distal part of the prosomal appendages was missing and the labrum was completely absent. Thus, Dll also plays a crucial role in labrum formation. However, the complete lack of labrum in RNAi embryos may point to a different nature of the labrum from the segmental appendages. Our data show that the expression of Dll in the appendages is conserved among arthropods, and furthermore that the role of Dll is evolutionarily conserved in the formation of segmental appendages in arthropods.

Expression patterns of hairy, even-skipped, and runt in the spider Cupiennius salei imply that these genes were segmentation genes in a basal arthropod.

There is an ongoing discussion on whether segmentation in different phyla has a common origin sharing a common genetic program. However, before comparing segmentation between phyla, it is necessary to identify the ancestral condition within each phylum. Even within the arthropods it is not clear which parts of the genetic network leading to segmentation are conserved in all groups. In this paper, we analyze the expression of three segmentation genes of the pair-rule class in the spider Cupiennius salei. Spiders are representatives of the Chelicerata, a monophyletic basic arthropod group. We find that in spider embryos, the orthologues for the Drosophila primary pair-rule genes hairy, even-skipped, and runt are expressed in stripes in the growth zone, where the segments are forming, suggesting a role for these genes in chelicerate segmentation. These data imply that the involvement of hairy, even-skipped, and runt in arthropod segmentation is an ancestral character for arthropods and is not restricted to a particular group of insects.

Abdominal-B expression in a spider suggests a general role for Abdominal-B in specifying the genital structure.

We have cloned an Abdominal-B (Abd-B) orthologue from the spider Cupiennius salei and have analysed its expression pattern during embryogenesis. An early expression domain is seen in the posterior part of the embryo, with an initial border in the third opisthosomal segment and later in the fifth opisthosomal segment. During mid-stage of germ band extension, two additional spots of expression appear in the posterior parts of the limb buds on the second opisthosomal segment. These coincide with the position of the future genital opening and Cs-Abd-B remains expressed in these regions until the openings are formed. In view of the fact that Abd-B and its orthologous genes are also required for specifying the genitalia in Drosophila and vertebrates, we suggest that this function may constitute an independent and ancestral role of Abd-B that can be separated from its role in specifying the posterior part of the body region.

A Hox class 3 orthologue from the spider Cupiennius salei is expressed in a Hox-gene-like fashion.

The class 3 Hox gene orthologue in insects, zerknüllt (zen), is not expressed along the anterior-posterior axis, but only in extra-embryonic tissues, suggesting that it has lost its function as a normal Hox gene. To analyse whether this loss of Hox gene function has already occurred in a basal arthropod lineage, we have isolated a Hox3 orthologue from the spider Cupiennius salei. In contrast to the insect zen sequences, which have a highly diverged homeobox, the spider Hox3 gene orthologue, Cs-Hox3, shows a high sequence similarity to the class 3 Hox genes of other phyla, including chordates. In situ hybridization in early embryos shows that it is expressed in a continuous region covering the pedipalp segment and the four leg-bearing segments. This expression pattern suggests a Hox-gene-like function for Cs-Hox3. On the other hand, the expression pattern does not strictly follow the colinearity rule, as it overlaps fully with the expression domain of the class 1 orthologue of the spider, Cs-lab. Still, our data suggest that the ancestor of the arthropods must have had a class 3 Hox gene with a function in anterior-posterior axis specification and that this function has been lost in the lineage leading to the insects.

A conserved mode of head segmentation in arthropods revealed by the expression pattern of Hox genes in a spider.

Chelicerates constitute a basic arthropod group with fossil representatives from as early as the Cambrian period. Embryonic development and the subdivision of the segmented body region into a prosoma and an opisthosoma are very similar in all extant chelicerates. The mode of head segmentation, however, has long been controversial. Although all other arthropod groups show a subdivision of the head region into six segments, the chelicerates are thought to have the first antennal segment missing. To examine this problem on a molecular level, we have compared the expression pattern of Hox genes in the spider Cupiennius salei with the pattern known from insects. Surprisingly, we find that the anterior expression borders of the Hox genes are in the same register and the same relative segmental position as in Drosophila. This contradicts the view that the homologue of the first antennal segment is absent in the spider. Instead, our data suggest that the cheliceral segment is homologous to the first antennal segment and the pedipalpal segment is homologous to the second antennal (or intercalary) segment in arthropods. Our finding implies that chelicerates, myriapods, crustaceans, and insects share a single mode of head segmentation, reinforcing the argument for a monophyletic origin of the arthropods.

Micromere formation at third cleavage is decisive for trochoblast specification in the embryogenesis of Patella vulgata.

Trochoblasts of the mollusc Patella vulgata differentiate early in development into ciliated cells due to a cell intrinsic developmental capacity. The third cleavage appears to be decisive for their specification. Permanent inhibition of cleavage after the third cleavage, as induced by a continuous incubation with the drug Cytochalasin B, had no effect on trochoblast-specific gene expression later in development. However, permanent inhibition of cleavage before third cleavage abolished trochoblast differentiation including trochoblast-specific gene expression. Inhibition of just the third cleavage itself was sufficient to repress trochoblast-specific gene expression. In contrast, inhibiting the second or fourth cleavage did not effect trochoblast-specific gene expression. Correct formation of micromeres at the third cleavage is required to obtain trochoblast-specific gene expression as was shown in experiments in which the formation of micromeres during third cleavage was suppressed by pressure. In addition, centrifugation before or during the third cleavage disturbs trochoblast-specific gene expression, whereas centrifugation after the third cleavage does not affect trochoblast-specific gene expression. Thus, during the third cleavage a decisive step in the determination of developmental fate of trochoblasts takes place, likely resulting in a segregation of activating and inhibitory determinants. Trochoblast-specific markers in Patella were only expressed in embryos that were division arrested after third cleavage. This suggests that a segregation of differentiation potentials has to take place before trochoblast differentiation markers are expressed. The restriction of differentiation potentials in the cleaving stage embryo is thus required to enable trochoblast-specific gene expression.

Multiple cis-acting elements act cooperatively in directing trochoblast-specific expression of the alpha-tubulin-4 gene in Patella embryos.

During early embryogenesis of the mollusc Patella vulgata the alpha-tubulin-4 gene is specifically expressed in the differentiation process of a particular cell type, the trochoblasts. The 5' region of the gene has been analysed for elements that are required for the regulation of the cell-type-specific activation of the gene. In a functional assay, seven elements that play a role in the spatiotemporal activation of the gene were detected in the promoter sequence. They are not required all together at the same time. A core of two elements, together with two or three auxiliary elements, are sufficient in controlling trochoblast-specific expression of the gene in the Patella embryo. One of the core elements is always required, without it, the gene is not expressed at all. The other core element acts as a positive element in trochoblasts and as a negative element in non-trochoblasts and thus is involved in directing the cell-type specificity of expression. The seven elements act cooperatively, and at least some of them can substitute for each other. Sequence comparison revealed that six of the seven fragments contain the sequence element GTTAA, including one of the core elements. Both core elements seem to play a crucial role in the expression of the alpha-tubulin-4 gene during the differentiation process of trochoblasts in the Patella embryo. A model for the regulation of the cell-type specificity of the gene during trochoblast differentiation is proposed.

Transcriptional regulation of tubulin gene expression in differentiating trochoblasts during early development of Patella vulgata.

The expression of alpha- and beta-tubulin genes during the early development of the marine mollusk Patella vulgata has been investigated. From the 32-cell stage onwards, an enhanced expression of both alpha- and beta-tubulin mRNAs was detected in the primary trochoblasts. After one additional cleavage, these cells become cleavage-arrested and then form cilia. They are the first cells to differentiate during Patella development. Later, alpha- and beta-tubulin mRNA is also found in the accessory and secondary trochoblasts. Together these three cell-lines form the prototroch, the ciliated locomotory organ of the trochophore larva. The early and abundant expression of tubulin genes precede and accompany cilia formation in the trochoblasts and provides us with an excellent molecular differentiation marker for these cells. Apart from the trochoblasts, tubulin gene expression was also found in other cells at some stages. At the 88-cell stage, elevated tubulin mRNA levels were found around the large nucleus of the mesodermal stem cell 4d. In later stages, tubulin gene expression was detected in the cells that form the flagella of the apical tuft and in the refractive bodies. An alpha-tubulin gene was isolated and characterized. A lacZ fusion gene under control of the 5' upstream region of this tubulin gene was microinjected into embryos at the two-cell stage. The reporter gene product was only detected in the three trochoblast cell-lines at the same time as tubulin genes were expressed in these cells. Reporter gene product was not detected in any other cells. Thus, this 5' upstream region of this alpha-tubulin gene contains all the elements required for the correct spatiotemporal pattern of expression.

Detection and occurrence of the 60- and 52-kD Ro (SS-A) antigens and of autoantibodies against these proteins.

The simultaneous detection of anti-La, anti-60-kD Ro and anti-52-kD Ro antibodies by immunoblotting is greatly improved by changing the crosslinking level in the gel to an acrylamide/bisacrylamide ratio of 19:1. Using this method for the analysis of a number of systemic lupus erythematosus (SLE) and Sjögren's syndrome patient sera it was observed that antibody to the 52-kD Ro protein without anti-60-kD Ro antibody was restricted to Sjögren's syndrome patients (9/26), whereas antibody to the 60-kD Ro protein without contaminating anti-52-kD Ro antibody was only found in SLE patients (8/38). Moreover, in Sjögren's syndrome patient sera anti-Ro antibody was found only in combination with anti-La antibody (20/26), whereas in SLE patient sera anti-Ro antibody could be found without detectable anti-La specificity (4/38). Double immunofluorescence microscopy revealed that the 52-kD Ro and the 60-kD Ro proteins co-localize in the cytoplasm as well as in the nucleus, whereas immunoprecipitation of [32P]-labelled HeLa cell extract with monospecific anti-52-kD Ro and anti-60-kD Ro sera showed that both proteins are associated with the Ro RNAs. These data suggest the presence of both the 52-kD and the 60-kD Ro proteins in the same ribonucleoprotein complexes. To study the evolutionary conservation of the 52-kD Ro, the 60-kD Ro and the La proteins, extracts of cell lines derived from various mammalian species were analysed on Western blots using monospecific human antibodies. In contrast to the 60-kD Ro and the La antigens which are well conserved in evolution, the 52-kD Ro antigen could be detected in primate cells only by this immunological approach.

Stimulation of the methylcoenzyme M reduction by uridine-5'-diphospho-sugars in cell-free extracts of Methanobacterium thermoautotrophicum (strain delta H).

The hydrogen-dependent reduction of methylcoenzyme M catalyzed by coenzyme-depleted cell-free extracts of Methanobacterium thermoautotrophicum was stimulated by micromolar concentrations of a UDP-disaccharide present in the organism. The compound was isolated and identified as UDP-1-O-alpha-D-2-acetamido-2-deoxyglucopyranose (UDPGlcpNAc) glycosidically linked to 2-acetamido-2-deoxymannopyranosyluronic acid. Maximal stimulation was observed when both the UDP-disaccharide and mercaptoheptanoylthreonine phosphate were present in the reaction mixtures. The UDP derivative isolated was not specific in its action: other UDP-sugars tested in micromolar concentrations stimulated the methylcoenzyme M reduction to the same extent. The activated sugars presumably substitute for ATP, which is usually required in much higher concentrations to activate the methylcoenzyme M reductase system.