Segmentally homologous neurons acquire two different terminal neuropeptidergic fates in the Drosophila nervous system.

In this study, we identify the means by which segmentally homologous neurons acquire different neuropeptide fates in Drosophila. Ventral abdominal (Va)-neurons in the A1 segment of the ventral nerve cord express DH31 and AstA neuropeptides (neuropeptidergic fate I) by virtue of Ubx activity, whereas the A2-A4 Va-neurons express the Capa neuropeptide (neuropeptidergic fate II) under the influence of abdA. These different fates are attained through segment-specific programs of neural subtype specification undergone by segmentally homologous neurons. This is an attractive alternative by which Hox genes can shape Drosophila segmental neural architecture (more sophisticated than the previously identified binary "to live" or "not to live" mechanism). These data refine our knowledge of the mechanisms involved in diversifying neuronal identity within the central nervous system.

A genetic strategy to obtain P-Gal4 elements in the Drosophila Hox genes.

The Drosophila Gal4/UAS system allows the expression of any gene of interest in restricted domains. We devised a genetic strategy, based on the P-element replacement and UAS-y (+) techniques, to generate Gal4 lines inserted in Hox genes of Drosophila that are, at the same time, mutant for the resident genes. This makes possible to express different wild-type or mutant Hox proteins in the precise domains of Hox gene expression, and thus to test the functional value of these proteins in mutant rescue experiments.

A targeted genetic screen identifies crucial players in the specification of the Drosophila abdominal Capaergic neurons.

The central nervous system contains a wide variety of neuronal subclasses generated by neural progenitors. The achievement of a unique neural fate is the consequence of a sequence of early and increasingly restricted regulatory events, which culminates in the expression of a specific genetic combinatorial code that confers individual characteristics to the differentiated cell. How the earlier regulatory events influence post-mitotic cell fate decisions is beginning to be understood in the Drosophila NB 5-6 lineage. However, it remains unknown to what extent these events operate in other lineages. To better understand this issue, we have used a very highly specific marker that identifies a small subset of abdominal cells expressing the Drosophila neuropeptide Capa: the ABCA neurons. Our data support the birth of the ABCA neurons from NB 5-3 in a cas temporal window in the abdominal segments A2-A4. Moreover, we show that the ABCA neuron has an ABCA-sibling cell which dies by apoptosis. Surprisingly, both cells are also generated in the abdominal segments A5-A7, although they undergo apoptosis before expressing Capa. In addition, we have performed a targeted genetic screen to identify players involved in ABCA specification. We have found that the ABCA fate requires zfh2, grain, Grunge and hedgehog genes. Finally, we show that the NB 5-3 generates other subtype of Capa-expressing cells (SECAs) in the third suboesophageal segment, which are born during a pdm/cas temporal window, and have different genetic requirements for their specification.

Lineage-unrelated neurons generated in different temporal windows and expressing different combinatorial codes can converge in the activation of the same terminal differentiation gene.

It is becoming increasingly clear that the activation of specific terminal differentiation genes during neural development is critically dependent upon the establishment of unique combinatorial transcription factor codes within distinct neural cell subtypes. However, it is still unclear to which extent these codes are shared by lineage-unrelated neurons expressing the same terminal differentiation genes. Additionally, it is not known if the activation of a specific terminal differentiation gene is restricted to cells born at a particular developmental time point. Here, we utilize the terminal differentiation gene FMRFa which is expressed by the Ap4 and SE2 neurons in the Drosophila ventral nerve cord, to explore these issues in depth. We find that the Ap4 and SE2 neurons are generated by different neural progenitors and use different combinatorial codes to activate FMRFa expression. Additionally, we find that the Ap4 and SE2 neurons are generated in different temporal gene expression windows. Extending the investigation to include a second Drosophila terminal differentiation gene, Leucokinin, we find similar results, suggesting that neurons generated by different progenitors might commonly use different transcription factor codes to activate the same terminal differentiation gene. Furthermore, these results imply that the activation of a particular terminal differentiation gene in temporally unrestricted.