Dynamic EGFR-Ras signalling in Drosophila leg development.

In Drosophila, as in many other animals, EGFR-Ras signalling has multiple developmental roles from oogenesis to differentiation. In leg development, in particular, it has been described to be responsible for the establishment of distal leg fates in a graded manner. Here, we investigate the patterns of expression of activators of EGFR-Ras signalling, as well as some of the effectors, in order to better understand the patterning of the distal leg, and to investigate further roles of this signalling pathway. These patterns, together with genetic data obtained by different mutant conditions for EGFR-Ras members and transgene expression, suggest two rounds of signalling in leg development. Early, the EGFR ligand Vein is the main player in distal leg patterning, possibly supported later by another ligand activated by Rhomboid. Later, in a second wave of signalling when all the proximal-distal leg fates have been specified, domains of EGFR/Ras activation appear inside each leg segment to regulate Notch-mediated joint development, and also some organs such as tendons and sensory organs. This second wave relies on a ligand activated by Rhomboid.

Leg patterning driven by proximal-distal interactions and EGFR signaling.

wingless and decapentaplegic signaling establishes the proximal-distal axis of Drosophila legs by activating the expression of genes such as Distalless and dachshund in broad proximal-distal domains during early leg development. However, here we show that wingless and decapentaplegic are not required throughout all of proximal-distal development. The tarsus, which has been proposed to be an ancestral structure, is instead defined by the activity of Distalless, dachshund, and a distal gradient of epidermal growth factor receptor (EGFR)-Ras signaling. Our results uncover a mechanism for appendage patterning directed by genes expressed in proximal-distal domains and possibly conserved in other arthropods and vertebrates.

Sequences homologous to the hobo transposable element in E strains of Drosophila melanogaster.

Hobo is one of the three Drosophila melanogaster transposable elements, together with the P and I elements, that seem to have recently invaded the genome of this species. Surveys of the presence of hobo in strains from different geographical and temporal origins have shown that recently collected strains contain complete and deleted elements with high sequence similarity (H strains), but old strains lack hobo elements (E strains). Besides the canonical hobo sequences, both H and E strains show other poorly known hobo-related sequences. In the present work, we analyze the presence, cytogenetic location, and structure of some of these sequences in E strains of D. melanogaster. By in situ hybridization, we found that euchromatic hobo-related sequences were in fixed positions in all six E strains analyzed: 38C in the 2L arm; 42B and 55A in the 2R arm; 79E and 80B in the 3L arm; and 82C, 84C, and 84D in the 3R arm. Sequence comparison shows that some of the hobo-related sequences from Oregon-R and iso-1 strains are similar to the canonical hobo element, but their analysis reveals that they are substantially diverged and rearranged and cannot code for a functional transposase. Our results suggest that these ubiquitous hobo-homologous sequences are immobile and are distantly related to the modern hobo elements from D. melanogaster.

Proximal-distal leg development in Drosophila requires the apterous gene and the Lim1 homologue dlim1.

Proximal-distal leg development in Drosophila involves a battery of genes expressed and required in specific proximal-distal (PD) domains of the appendage. Here we report the characterisation of a new gene of this type, dlim1, a member of the Lhx family of genes whose proteins contain two Lim domains and a homeodomain. We show that the Lhx gene apterous (ap) is also required for PD leg development, and we study the functional interactions between ap, dlim1 and other PD genes during leg development. Our results show that a regulatory network formed by ap and dlim1 plus the homeobox genes aristaless and Bar specifies distal leg cell fates in Drosophila.

Intercalation of cell fates during tarsal development in Drosophila.

The process of proximal-distal (PD) patterning in animal appendages requires the generation of positional values as they grow away from the main body axes. In the Drosophila leg some PD fates are intercalated between previously existing ones. In a recent study, Kojima et al. describe a role for the homeobox gene Bar in patterning of the distal region of the leg. Their work highlights fundamental aspects of PD development, such as the fashion in which new PD values appear, the importance of regulatory relationships between PD genes, and correlation of their patterns of expression with morphogenesis and differentiation.

Ultrastructure of regions containing homologous loci in polytene chromosomes of Drosophila melanogaster and Drosophila subobscura.

We have used a new approach involving in situ hybridisation and electron microscopy to establish ultrastructural homologies between polytene chromosome regions of Drosophila melanogaster and Drosophila subobscura. Twelve probes were chosen to cover all the chromosomal elements: the myospheroid gene, the collagen type IV gene, the collagen-like gene, the w26 homeobox gene, the beta3 tubulin gene, the kinesin heavy chain gene, the tryptophan hydrolase gene, the Hsp82, Hsp22-26 and Hsp23-28, Hsp68, Hsp70 genes and the beta unit of the F0-F1 ATPase gene. Most of these loci were previously undescribed in D. subobscura and imprecisely located in D. melanogaster. We have demonstrated here, by an ultrastructural analysis of each chromosomal region, that homologous genetic loci tend to show a similar ultrastructure in the two species. With a few exceptions, the structural homology extends to the chromosomal regions surrounding the loci. In some cases, however, no structurally recognisable homology can be seen either in the locus or in its flanking regions.

Spread of the autonomous transposable element hobo in the genome of Drosophila melanogaster.

The transposable element hobo has been introduced into the previously empty Drosophila melanogaster strain Hikone so that its dynamics can be followed and it can be compared with the P element. Five transformed lines were followed over 58 generations. The results were highly dependent on the culture temperature, the spread of hobo element being more efficient at 25 degrees C. The multiplication of hobo sequences resulted in a change in the features of these lines in the hobo system of hybrid dysgenesis. The number of hobo elements remained low (two to seven copies) and the insertions always corresponded to complete sequences. Our findings suggest that, despite their genetic similarities, P and hobo elements differ in many aspects, such as mobility and regulation mechanisms.

Invasion of the hobo transposable element studied by in situ hybridization on polytene chromosomes of Drosophila melanogaster.

The invasion kinetics of hobo transposable element in the Drosophila melanogaster genome was studied by in situ hybridization on the polytene chromosomes. Six independent lines of Drosophila melanogaster flies that had been previously transformed by microinjection of the pHFL1 plasmid containing a complete hobo element were followed over 50 generations. We observed that hobo elements were scattered on each of the chromosome arms, with more insertion sites on the 3R arm. The total number of insertion sites remains quite small, between four and six, at generation 52. On the 2R arm, a short inversion appeared once at generation 52. Most of the integration sites reported here were already described for several transposons but some of them appear to be hotspots for hobo elements.

The evolutionary genetics of the hobo transposable element in the Drosophila melanogaster complex.

Hobo elements are a family of transposable elements found in Drosophila melanogaster and its three sibling species: D. simulans, D. mauritiana and D. sechellia. Studies in D. melanogaster have shown that hobo may be mobilized, and that the genetic effects of such mobilizations included the general features of hybrid dysgenesis: mutations, chromosomal rearrangements and gonadal dysgenis in F1 individuals. At the evolutionary level some hobo-hybridizing sequences have also been found in the other members of the melanogaster subgroup and in many members of the related montium subgroup. Surveys of older collected strains of D. melanogaster suggest that complete hobo elements were absent prior to 50 years ago and that they have recently been introduced into this species by horizontal transfer. In this paper we review our findings and those of others, in order to precisely describe the geographical distribution and the evolutionary history of hobo in the D. melanogaster complex. Studies of the DNA sequences reveal a different level of divergence between the group D. melanogaster, D. simulans and D. mauritiana and the fourth species D. sechellia. The hypothesis of multiple transfers in the recent past into the D. melanogaster complex from a common outside source is discussed.

[Mail handling: a possible cause of error in the non-selective screening for congenital hypothyroidism]. / Envío por correo: una posible causa de error en el "screening" no selectivo del hipotiroidismo congénito.

Remittance by mail of blood samples and subsequent time of permanency in mail boxes are not supposed to be best thermic conditions for dried blood samples in paper used for neonatal screening. With the idea of checking if temperatures variations can altered or not the content of TSH and T4, some samples of known concentrations of TSH and T4 has been heated to different temperatures between less than -40 degrees C and 100 degrees C during weekly periods. At such temperatures between less than -40 degrees C and 25 degrees C significant hormones losses are not observed. Nevertheless under higher temperatures the percentages of losses increases. Specifically between 37 degrees C and 60 degrees C an hormonal loss of approximately 36% is observed. T4 had also suffered losses of concentration in relation with temperature. These variations make indispensable the change of the way of managing samples that could had suffered modifications with temperatures, and that have been sent by mail. Therefore, considering that about a 40% loss can exist, limit of 40 mu UI/ml should be modified about 25 mu UI/ml.