Ultrabithorax Sculpts Haltere in Drosophila melanogaster
To begin the new section “Classics”,where i discuss some outstanding papers in the field .we will look into an article from Weatherbee et al published in genes and dev in 1998.This article comes the lab of Sean carroll ,considered to be temple of evo devo, forms one reason for selecting this article as a starter for this section .The other reason being this kind of work is pretty close to my heart because my first experience with fruit flies and research world came from a project on similar lines.I worked initially on a downstream target of Hox gene Ultrabithorax which was differentially expressed between wing and haltere imaginal discs.
Vertebrates and Arthropods are made up of serially homologus structures each governed by different Hox genes.The development and differentiation of haltere (a balancing organ in fly present in third thoracic segment)from homologous Wing is mediated by Hox gene Ultrabithorax (Ubx) is a classic example of Hox regulation of homologous structures and has served as the paradigm for understanding the nature of homeotic gene function.The differential development between wing and haltere constitutes a good genetic system to study cell fate determination at various levels such as growth, cell shapes and its biochemical properties and physiological properties. They also represent evolutionary trends that has established difference between fore and hind limbs in mammals including humans,wings and legs in birds.
This work is arguably the best study published so far on how gene regulation differs in homologous structures like wing and haltere.Mutations of Ubx result in transformation of the dorsal appendages of the third thoracic segment (haltere ) into their counterparts on the second thoracic segment(Wing).
There are two organizing centers namely Anterior posterior boundary (which forms first in development) and Dorso ventral boundary(DV) . They act as source for morphogens which plays a vital role in patterning the wing discs.Morphogens diffuse and activate various targets in a concentration dependent manner.AP boundary is the source of two morphogens 1) Hedgehog(Hh) :which is a short range morphogen and 2) decapantaplegic(dpp) which is activated by Hh it has the potential to diffuse in a wide range.Wingless another long range morphogen diffuses from DV boundary.In this way these morphogens takes care of patterning across the wing field.
Results from the study obtained by virtue of some excellent genetic experiments indicate that Ubx down regulates DV morphogen wingless in posterior compartment of haltere and at also acts downstream of dpp pathway by repressing splat (r).The major contribution of ubx for shaping haltere comes from repressing Quadrant enhancer of vestegial (Pro wing gene) This is interesting as Ubx selectively repress only quandrant enhancer of Vestegial leaving boundary enhancer untouched.
The Drosophila Serum Response Factor (DSRF or blistered) gene is expressed in future inter vein tissue(remember haltere is a balloon like structure lacks veins and inter veins like wing) and required for the adhesion of the dorsal and ventral surfaces of the flat wing.Ubx also repress DSRF in haltere.
Another marked difference between wing and haltere is presence of sensory bristles along the margin which are conspicuous by their absence in haltere.The formation of margin bristles is regulated by Wg via the induction of the proneural achaete (ac) and scute (sc) target genes.This paper also provides evidence for repression of achaete-scute complex by Ubx in ahltere discs.
The siginificant outcome of this work is that Ubx represses wing development through the independent regulation of target genes at multiple levels of regulatory hierarchies,which could be the case for other Hox genes regulating homologous structures in other animals.
This article can be freely downloaded now from the genes and development web page.
Subsequent work in this field also showed that Ubx also down regulates EGFR (Pallavi et al DEV BIOL 2006) and Dpp pathway (Independently shown by three labs of LS Shashidhara,Ernesto Sanchez Herrero and Richard Mann)
Referneces:
Scott D. Weatherbee, Georg Halder, Jaeseob Kim, Angela Hudson, and Sean Carroll
Ultrabithorax regulates genes at several levels of the wing-patterning hierarchy to shape the development of the Drosophila haltere
Genes Dev. 1998 12: 1474-1482
S.K. Pallavi, Ramakrishnan Kannana and L.S. Shashidhara
Negative regulation of Egfr/Ras pathway by Ultrabithorax during haltere development in Drosophila
Developmental Biology Volume 296, Issue 2, 15 August 2006, Pages 340-352
Kalpana Makhijani, Chilukuri Kalyani, Tamarisa Srividya, L S Shashidhara
Modulation of Decapentaplegic gradient during haltere specification in Drosophila.
Dev Biol. 2007 Feb 1;302(1):243-55.
de Navas LF, Garaulet DL, Sánchez-Herrero E.
The ultrabithorax Hox gene of Drosophila controls haltere size by regulating the Dpp pathway.
Development. 2006 Nov;133(22):4495-506.
Mohit P, Makhijani K, Madhavi MB, Bharathi V, Lal A, Sirdesai G, Reddy VR, Ramesh P, Kannan R, Dhawan J, Shashidhara LS.
Modulation of AP and DV signaling pathways by the homeotic gene Ultrabithorax during haltere development in Drosophila.
Dev Biol. 2006 Mar 15;291(2):356-67.
Crickmore MA, Mann RS.
Hox control of organ size by regulation of morphogen production and mobility.
Science. 2006 Jul 7;313(5783):63-8.
(RED QVG and Wg Green) and DSRF in wing discs
Related Posts:
If you liked what you just read, you may want to subscribe to my
RSS FEED
Thanks for visiting!
Leave your response!