Segmental organisation of the tail region in the embryo of Drosophila melanogaster

Summary The segmental organisation of the tail region in the embryo of Drosophila melanogaster, which is defined here as the epidermal region posterior to the boundary between abdominal segments A7 and A8, has been investigated by means of ultraviolet (UV) laser fate-mapping and phenotypic analysis of embryonic mutants that alter the segmental pattern of the larval cuticle. Wild-type embryos were irradiated in the presumptive tail region with a UV- laser microbeam of 20 m diameter at the blastoderm stage. The ensuing defects were scored in the cuticle pattern of the tail region of the first-instar larva, which is described in detail in this paper. The spatial distribution of defect frequencies was used to construct a blastoderm fate-map of the cuticle structures of the larval tail region. The segmental origin of the larval tail structures was inferred from the phenotypic analysis of segmentation and homoeotic mutants, which revealed pattern repetition throughout the embryonic tail region corresponding to four segment anlagen, A8 to A11, and a non-segmental telson. These data enabled the transformation of the blastoderm fate-map of cuticle structures into a map of tail segment anlagen. The tail anlage occupies about 10% of the egg length (EL), bounded by segment A7 anteriorly at 20% EL and by the proctodaeum posteriorly at 10% EL, as measured from the posterior pole. The anlagen of segments A8 and A9 appear to be narrow dorso-ventral strips of blastoderm cells similar to the anlagen of the trunk segments, whereas the anlagen of A10 and A11 are smaller and produce fewer pattern elements. The telson is represented in the cuticle by the tuft which derives from a very dorsal posterior position. The antero-posterior axis of the entire tail anlage appears curved upward posteriorly. Differences in the mode of development between tail and trunk segments are discussed, as are similarities of larval and imaginal tail development in Drosophila. Comparison with tail development in other insects suggests that, during evolution, the transition from semi-long-germ to long-germ development modified the organisation of the tail region without affecting its primary subdivision into metameric units.     

Morphogenesis of the tail of bacteriophage lambda. III. Morphogenetic pathway.

Precursors of the tail of bacteriophage λ have been detected by measurements of in vitro complementation activities and serum blocking activity in sucrose gradients of lysates defective in tail genes.On the basis of these measurements, a pathway for the assembly of the λ tail is proposed:The morphogenesis of the λ tail starts from the tail fiber (product of gene J) located at the distal end of the tail, and proceeds to the proximal end. Gene J by itself produces a 15 S structure with serum blocking activity but without any detectable in vitro complementation activity, which may be the least advanced precursor of the λ tail or an abortive product. Functions of genes J, I, K, L are required for the formation of a 15 S precursor that has in vitro complementation activities with J⁻, I⁻, K⁻ and L⁻ lysates and serum blocking activity. If the products of genes G and H act on the latter 15 S precursor, a 25 S precursor is made, but this precursor seems either to be in equilibrium with the 15 S precursor or to degrade easily into the 15 S precursor. Gene M has a function of stabilizing the 25 S precursor. After the action of gene M product, the 25 S precursor is ready to serve as a nucleus on which the product of gene V (the major tail protein) assembles. However, gene U product is also necessary at this step for the correct assembly of the major tail protein on the 25 S precursor. Without gene U product the assembly of the major tail protein does not stop at the correct length and a polytail is formed instead of a morphologically normal tail. Finally, gene Z product acts on the morphologically normal tail and makes it a biologically active tail. Without the action of gene Z product, the defective tail binds to a head and forms a phage-like particle which is only very weakly infectious. (The position of gene T in the pathway is not determined, because no sus mutant is available in gene T.)Two abnormal, less efficient pathways are also present in vitro. (1) If gene U product acts on a polytail in an U⁻ lysate, the polytail finally binds to a head and forms a phage particle with an extra long tail which is infectious to a small extent. (2) The function of gene K seems to be bypassed to some extent: K⁻ lysates accumulate particles which sediment as fast as normal phage and which are complemented by other tail⁻ lysates.     

Morphogenetic determination of the dermoepidermal interface during tail regeneration in Rana catesbeiana.

During regeneration of the amputated tadpole tail, reconstruction of the epithelial basal lamina and basement lamella occurs only after the other major morphogenetic processes are well established. At 4 days after tail transection of the bullfrog tadpole, electron microscopy of the internal surface of the basal cell layer of the blastemal epithelium reveals it to be relatively free of extracellular matrix. By 11 days a basal lamina of distinct regularity has formed, and the first rodlets and fibers signaling the replacement of the collagenous basement lamella are identified. At 15 days the basal cells of the epithelium start to exhibit specialization of their internal cell surfaces: Hemidesmosomes and associated tonofilaments appear, and the adepidermal globular layer is formed. Orthogonal packing of collagen plies begins by 19 days after transection, the number of layers exceeding 22 in the latter stages of regeneration.     

Identification of six phosphorylation sites in the COOH-terminal tail region of the rat neurofilament protein M.

The COOH-terminal tail domain of the neurofilament polypeptide M from rat nervous tissue contains approximately six molecules of phosphate. We report here that protein kinases in a crude cytoskeleton preparation of rat nervous tissue phosphorylated a set of tryptic peptides of M similar (but not identical) to those phosphorylated by living dorsal root ganglion cells in culture. Using these phosphopeptides as markers, we purified these same peptides from rat spinal cord and identified six specific phosphorylation sites in M by enzymatic and chemical criteria. These sites, serines 502, 506, 536, 606, 608, and 666, are all located in the COOH-terminal tail domain. Four are embedded in the repeated motif KSP whereas two are within variants of this motif, KSD and ESP. All of the sites that were preceded by lysine were resistant to alkaline phosphatase prior to modification of the lysine with citraconic anhydride. The identification of these sites should aid in investigations of the function of the phosphorylation of this protein and provides criteria for identifying the relevant kinases.     

Heat vasodilatation of the rat tail.

The vasomotor response of the tail of the albino rat to total-body heating and cooling was studied by skin-temperature recording and plethysmography with the tail at 25 degrees C air temperature. Tail vasodilation started at core temperatures lightly above 37 degrees C and increased to a core temperature up to about 39 degrees C. During cooling of warm rats, tail vasoconstriction started at significantly higher levels of core temperature than the values at which vasodilation appeared when the rat was warmed.     

Curvature of the caudal region is responsible for failure of neural tube closure in the curly tail (ct) mouse embryo.

Delayed closure of the posterior neuropore (PNP) occurs to a variable extent in homozygous mutant curly tail (ct) mouse embryos, and results in the development of spinal neural tube defects (NTD) in 60% of embryos. Previous studies have suggested that curvature of the body axis may delay neural tube closure in the cranial region of the mouse embryo. In order to investigate the relationship between curvature and delayed PNP closure, we measured the extent of ventral curvature of the neuropore region in ct/ct embryos with normal or delayed PNP closure. The results show significantly greater curvature in ct/ct embryos with delayed PNP closure in vivo than in their normal littermates. Reopening of the posterior neuropore in non-mutant mouse embryos, to delay neuropore closure experimentally, did not increase ventral curvature, suggesting that increased curvature in ct/ct embryos is not likely to be a secondary effect of delayed PNP closure. Experimental prevention of ventral curvature in ct/ct embryos, brought about by implantation of an eyelash tip longitudinally into the hindgut lumen, ameliorated the delay in PNP closure. We propose, therefore, that increased ventral curvature of the neuropore region of ct/ct embryos imposes a mechanical stress, which opposes neurulation and thus delays closure of the PNP. Increased ventral curvature may arise as a result of a cell proliferation imbalance, which we demonstrated previously in affected ct/ct embryos.     

Graded requirement for the zygotic terminal gene, tailless, in the brain and tail region of the Drosophila embryo

We have used hypomorphic and null tailless (tll) alleles to carry out a detailed analysis of the effects of the lack of tll gene activity on anterior and posterior regions of the embryo. The arrangement of tll alleles into a continuous series clarifies the relationship between the anterior and posterior functions of the tll gene and indicates that there is a graded sensitivity of anterior and posterior structures to a decrease in tll gene activity. With the deletion of both anterior and posterior pattern domains in tll null embryos, there is a poleward expansion of the remaining pattern. Using anti-horseradish peroxidase staining, we show that the formation of the embryonic brain requires tll. A phenotypic and genetic study of other pattern mutants places the tll gene within the hierarchy of maternal and zygotic genes required for the formation of the normal body pattern. Analysis of mutants doubly deficient in tll and maternal terminal genes is consistent with the idea that these genes act together in a common pathway to establish the domains at opposite ends of the embryo. We propose that tll establishes anterior and posterior subdomains (acron and tail regions, respectively) within the larger pattern regions affected by the maternal terminal genes.     

Morphogenetic control during tail regeneration in Plethodon cinereus: the role of skeletal muscle

The caudal myofibers of Plethodon cinereus do not appear to participate directly in epimorphic tail regeneration following either autotomy or surgical amputation of the tail. The possibility that tail musculature might indirectly influence morphogenesis of the regenerate was tested by unilaterally removing 99% of the lateral muscle mass for five to six caudal segments. Ten days after muscle ablation, tails were amputated through the deficient area. Unlike previous experiences with ambystomid larvae, P. cinereus regulates completely producing a normal tail regenerate and at a rate comparable to that following simple amputation.     

Perforations in the tail features of parasitic Cuckoos

Bouwman, H. 2000. Perforations in the tail features of parasitic Cuckoos. Ostrich 71 (1 & 2): 126.

Perforations in the tail feathers of parasitic cuckoos have been observed in both live and museum specimens. These perforations occurring in the vane of the feather, are longitudinally arranged, and in many cases evenly spaced. The position, arrangement and spacing suggest that the perforations were not caused by feather mites. Anecdotal evidence and literature suggests that these perforations are probably caused by host birds during confrontations. Quantification of perforations in terms of species, age, sex, increase in damage during the breeding season, and in damage from breeding and non-breeding areas, supports this hypothesis. The parasitic species that parasitisc birds with stronger beaks (weavers and shrikes) tended to have more damage.     

Structural features of the 26S proteasome complex isolated from rat testis and sperm tail

We have previously cloned a cDNA encoding TBP-1, a protein present in the rat spermatid manchette and outer dense fibers of the developing sperm. TBP-1 contains a heptad repeat of six-leucine zipper fingers at the amino terminus and highly conserved ATPase and DNA/RNA helicase motifs toward the carboxyl terminus. TBP-1 is one of the 20 subunits forming the 19S regulatory complex of the 26S proteasome, an ATP-dependent multisubunit protease found in most eukaryotic cells. We now report the isolation of the 26S proteasome from rat testis and sperm tail and its visualization by whole-mount electron microscopy using negative staining. The 26S proteasome from rat testis was fractionated by Sephacryl S-400/Mono-Q chromatography using homogenates suspended in a 10% glycerol-supplemented buffer. Chromatographic fractions were analyzed by immunoblotting using a specific anti-TBP-1 serum. During the purification of Sak57, a keratin filament present in outer dense fibers from epididymal sperm, we detected a substantial amount of 26S proteasomes. Intact 26S proteasomes from rat testis display a rod-shaped particles about 45 nm in length and 11-17 nm in diameter. Each particle consists of a 20S barrel-shaped component formed by four rings (alphabetabetaalpha), capped by two polar 19S regulatory complexes, each identified by an element known as the "Chinese dragon head motif". TBP-1 is an ATPase-containing subunit of the 19S regulatory cap. Rat sperm preparations displayed both dissociated 26S proteasomes and Sak57 filaments. We hypothesize that 26S proteasomes in the perinuclear-arranged manchette are in a suitable location for recognition, sequestration, and degradation of accumulating ubiquitin-conjugated somatic and transient testis-specific histones during spermiogenesis. In the sperm tail, the 26S proteasome may have a role in the remodeling of the outer dense fibers and other tail components during epididymal transit.     

Mesoderm induction in the future tail region of Xenopus

Summary We have used interspecific grafts between Xenopus borealis and Xenopus laevis to study the signalling system that produces tail mesoderm. Early gastrula ectoderm grafted into the posterior neural plate region of neurulae responds to a mesodermal inducing signal in this region and forms mainly tail somites; this signal persists until at least the early tail bud stage. Ventral ectoderm grafted into the posterior neural plate loses its competence to respond to this signal after stage 10 1/2. We have established the specification of anterior and posterior neural plate ectoderm. In ectodermal sandwiches or when grafted into unusual positions, anterior regions gave rise to mainly nervous system and posterior regions to large amounts of muscle, together with some nervous system. Thus it was impossible to assess the competence of posterior neural plate ectoderm to form further mesoderm and hence to establish if mesodermal induction continues during neurulation in unmanipulated embryos.