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Wednesday, 29th January 2020

Segmental specification and pattern formation in Drosophila


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Ernesto Sánchez-Herrero Arbide

CSciStaff

CPublications

 

Research summary:

fig01.300px

Figure 1. Drosophila female genital disc showing expression of brinker (in red), P-Mad (in blue) and bantam sensor (in green).

 

Video 1. Video showing the removal of the abdominal histoblasts of the male A7 (small cells in the upper lateral side) and the larval cells (large, centrally located). The A6 histoblasts abut the genitalia , which is in the inal steps of its 360° rotation (top).The cells are marked with neuroglian-GFP.

 

fig03.300px

Figure 2. Male genital disc in which death was induced in the caudal domain and regenerated afterwards. The expression of Caudal (red) is more limited than that of ß-galactosidase (green) marking the caudal lineage. Topro is in blue.

 

Video 2. The genital plate rotates 360º in pupa. The cells are marked with nrg-GFP (in green) and posterior cells with Hh-Dsred (in red).


One important question in developmental biology is to understand the mechanisms that control size, shape and pattern of different structures in each organism. Our aim is to study these issues in Drosophila melanogaster, with a special focus in the analysis of Hox genes. These genes specify the identity of different structures along the anteroposterior axis of all the bilaterians. The Hox genes code for proteins that bind DNA and regulate the expression of downstream genes, which eventually determine changes in form, size and pattern in different organs.

Control of shape of an organ by Hox genes

The wings and the halteres are homologous organs of the dorsal thorax of Drosophila, the wings being present in the second thoracic segment (or mesothorax), and the halteres in the third thoracic segment (or metathorax). The wings are flat while the halteres have a globular shape, and both shapes, flat and globular, are necessary for normal Drosophila flight. The different morphology of these appendices is due to the activity of the Hox gene Ultrabithorax (Ubx), present in the imaginal haltere disc but not in the wing one, during the pupal period. We study how Ubx determines the different wing and haltere shape by regulating integrins and extracellular matrix proteins to prevent the dorsal and ventral surfaces of the distal part of the haltere disc from apposing, as it occurs in the wing imaginal disk (Figure 1). 

The removal of an abdominal segment and the rotation of the genitalia

Drosophila males lack the seventh abdominal segment (A7) while females maintain it (although reduced). Although the cells that give rise to this segment are present during the larval period, in the pupal stage they are extruded in the males, and both the activity of the Abdominal-B Hox gene and the sexual determination genes are required for this process. We want to study how these genes regulate the process of elimination of this segment at a precise moment of pupation (video 1). The elimination of the end of the male's abdomen correlates with the correct rotation of the genital plate (which rotates 360º in the wildtype). This rotation is always dextral, and constitutes a model for the study of how left-right asymmetries are established (video 2). Abdominal larval cells, which contact the imaginal disc that will form the genitalia, die and are extruded from the epithelium in pupae, and we have discovered that in certain genetic combinations in which this extrusion is delayed the genital plate does not rotate correctly. This suggests there is signaling from the abdomen to the genital disc for the correct rotation of this structure.

Testes formation and left-right asymmetry.

Drosophila's testicles lengthen and spiral (always dextrally) in pupae when cells derived from the genital disc contact them. At the beginning of this process mesodermal cells migrate from this disk and surround the testicles while they lengthens. We have found that the Hox Abdominal-B gene is needed in these muscle cells, and that in its absence the testicles remain spherical and do not lengthen. The activation of different signaling pathways and the abdominal-A and Abdominal-B Hox genes are also necessary for the elongation of testicles and their dextral spiraling.

Regeneration and Hox genes

Drosophila imaginal discs have been used as a model for studying processes of cell reprogramming. After damaging or removing parts of an imaginal disc there is recovery thereof mediated by different signals. It has been shown that during the regeneration of imaginal discs transgressions of compartments take place, with possible changes in cell identity, including those determined by Hox genes. To analyze this point, we are to study the changes of expression of homeotic genes that occur during regeneration of the genital disc, an imaginal disc formed by the fusion of three segments with distinct homeotic information (Figure 2).

 


 

Relevant publications:

  • De Las Heras, J. M., García-Cortés, C., Foronda, D., Pastor-Pareja, J. C., Shashidhara, L. S., y  Sánchez-Herrero E. (2018). The Drosophila Hox gene Ultrabithorax  controls appendage shape by regulating extracellular matrix dynamics. Development 1

                      recommended in F1000  https://f1000.com/prime/733362447

        


 

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