"Anteroposterior Patterning: How the Hox Genes Help Us Tell Our Heads from Our ***es"

The fundamental problem of developmental biology is how a single cell- a fertilized egg- is able to produce an entire organism in all its complexity. One essential aspect of this process is spatial patterning-in essence, instructing cells as to their location in developing body so that they can exhibit characteristics appropriate to their functions. he Hox genes, first discovered in mutant fruit fly "hopeful monsters" with extra pairs of wings or legs growing out of their heads, confer spatial information along the anteroposterior axis in animals from worms to humans. Prof Marin's research focuses on the roles of specific Hox genes in sculpting the developing entral nervous system of the fruit fly and how the same gene can direct a neuron to die, survive, or send its axon in search of different connections, depending on cellular context.

Ultrabithorax Confers Spatial Identity in a Context-Specific Manner in the Drosophila Postembryonic Ventral Nervous System

In holometabolous insects such as Drosophila melanogaster, neuroblasts produce an initial population of diverse neurons during embryogenesis and a much larger set of adult-specific neurons during larval life. In the ventral CNS, many of these secondary neuronal lineages differ significantly from one body segment to another, suggesting a role for anteroposterior patterning genes. Here we systematically characterize the expression pattern and function of the Hox gene Ultrabithorax (Ubx) in all 25 postembryonic lineages. We find that Ubx is expressed in a segment-, lineage-, and hemilineage-specific manner in the thoracic and anterior abdominal segments. When Ubx is removed from neuroblasts via mitotic recombination, neurons in these segments exhibit the morphologies and survival patterns of their anterior thoracic counterparts. Conversely, when Ubx is ectopically expressed in anterior thoracic segments, neurons exhibit complementary posterior transformation phenotypes. Our findings demonstrate that Ubx plays a critical role in conferring segment-appropriate morphology and survival on individual neurons in the adult-specific ventral CNS. Moreover, while always conferring spatial identity in some sense, Ubx has been co-opted during evolution for distinct and even opposite functions in different neuronal hemilineages.