The Drosophila homeodomain transcription factor Homeobrain is involved in the formation of the embryonic protocerebrum and the supraesophageal brain commissure
“…1 D, E). In particular, the expression in domain DPM was very pronounced; here, DRx was more broadly expressed than Hbn, another factor expressed in that area [ 39 , 43 ]. Fig.…”
Section: Resultsmentioning
confidence: 99%
“…More recently, it was shown that DRx is also one of several transcription factors that are expressed in type II neuroblasts in the embryonic brain and important for progenitor cell proliferation leading to an expansion of the brain region compared with the ventral nerve cord [ 39 ]. Homeodomain transcription factors such as Orthopedia (Otp) [ 40 , 41 ] and Homeobrain (Hbn) [ 42 , 43 ] belong to these factors and are together with DRx encoded next to each other in the 57B region on the second chromosome [ 42 ]. Mutants of all these factors alone or in combination show a reduction in neuroblasts and the proliferation of their daughter cells.…”
Background
The Drosophila brain is an ideal model system to study stem cells, here called neuroblasts, and the generation of neural lineages. Many transcriptional activators are involved in formation of the brain during the development of Drosophila melanogaster. The transcription factor Drosophila Retinal homeobox (DRx), a member of the 57B homeobox gene cluster, is also one of these factors for brain development.
Results
In this study a detailed expression analysis of DRx in different developmental stages was conducted. We show that DRx is expressed in the embryonic brain in the protocerebrum, in the larval brain in the DM and DL lineages, the medulla and the lobula complex and in the central complex of the adult brain. We generated a DRx enhancer trap strain by gene targeting and reintegration of Gal4, which mimics the endogenous expression of DRx. With the help of eight existing enhancer-Gal4 strains and one made by our group, we mapped various enhancers necessary for the expression of DRx during all stages of brain development from the embryo to the adult. We made an analysis of some larger enhancer regions by gene targeting. Deletion of three of these enhancers showing the most prominent expression patterns in the brain resulted in specific temporal and spatial loss of DRx expression in defined brain structures.
Conclusion
Our data show that DRx is expressed in specific neuroblasts and defined neural lineages and suggest that DRx is another important factor for Drosophila brain development.
“…1 D, E). In particular, the expression in domain DPM was very pronounced; here, DRx was more broadly expressed than Hbn, another factor expressed in that area [ 39 , 43 ]. Fig.…”
Section: Resultsmentioning
confidence: 99%
“…More recently, it was shown that DRx is also one of several transcription factors that are expressed in type II neuroblasts in the embryonic brain and important for progenitor cell proliferation leading to an expansion of the brain region compared with the ventral nerve cord [ 39 ]. Homeodomain transcription factors such as Orthopedia (Otp) [ 40 , 41 ] and Homeobrain (Hbn) [ 42 , 43 ] belong to these factors and are together with DRx encoded next to each other in the 57B region on the second chromosome [ 42 ]. Mutants of all these factors alone or in combination show a reduction in neuroblasts and the proliferation of their daughter cells.…”
Background
The Drosophila brain is an ideal model system to study stem cells, here called neuroblasts, and the generation of neural lineages. Many transcriptional activators are involved in formation of the brain during the development of Drosophila melanogaster. The transcription factor Drosophila Retinal homeobox (DRx), a member of the 57B homeobox gene cluster, is also one of these factors for brain development.
Results
In this study a detailed expression analysis of DRx in different developmental stages was conducted. We show that DRx is expressed in the embryonic brain in the protocerebrum, in the larval brain in the DM and DL lineages, the medulla and the lobula complex and in the central complex of the adult brain. We generated a DRx enhancer trap strain by gene targeting and reintegration of Gal4, which mimics the endogenous expression of DRx. With the help of eight existing enhancer-Gal4 strains and one made by our group, we mapped various enhancers necessary for the expression of DRx during all stages of brain development from the embryo to the adult. We made an analysis of some larger enhancer regions by gene targeting. Deletion of three of these enhancers showing the most prominent expression patterns in the brain resulted in specific temporal and spatial loss of DRx expression in defined brain structures.
Conclusion
Our data show that DRx is expressed in specific neuroblasts and defined neural lineages and suggest that DRx is another important factor for Drosophila brain development.
“…Several transcription factors were identified that are important for the proliferation of type I and type II neuroblasts in the brain, leading to an expansion of the brain region compared with the ventral nerve cord [ 17 ]. They include Earmuff (Erm), belonging to the FEZ family of C2H2 Zinc finger transcription factors [ 18 ], Tailless (Tll), a nuclear receptor transcription factor [ 19 ], the T-box transcription factors Doc1/2/3 [ 20 ] as well as the three homeodomain transcription factors Orthopedia (Otp) [ 21 , 22 ], Drosophila Retinal homeobox (DRx) [ 23 , 24 ] and Homeobrain (Hbn) [ 25 , 26 ], clustered in the 57B region on the second chromosome. Mutants of all these factors alone or in combination show a reduction of neuroblasts and the proliferation of their daughter cells in the embryonic brain.…”
Section: Introductionmentioning
confidence: 99%
“…Upon misexpression, all of these transcription factors drive proliferation in the ventral nerve cord and even reprogram wing disc cells into brain neural progenitors [ 17 ]. The homeodomain transcription factor Hbn, which is one of these brain factors, was shown to be expressed in the embryo in several neuroblasts, in GMCs and in neurons located mainly in the protocerebrum [ 26 ]. These neuroblasts include type I neuroblasts and some type II neuroblasts [ 17 ].…”
Section: Introductionmentioning
confidence: 99%
“…In hbn mutants, large parts of the protocerebrum are missing and the supraesophageal commissure connecting both brain hemispheres is absent [ 26 ]. In addition, Hbn is expressed in the midgut of late embryos [ 25 ], with an apparent endocrine function.…”
Background
The homeobox gene homeobrain (hbn) is located in the 57B region together with two other homeobox genes, Drosophila Retinal homeobox (DRx) and orthopedia (otp). All three genes encode transcription factors with important functions in brain development. Hbn mutants are embryonic lethal and characterized by a reduction in the anterior protocerebrum, including the mushroom bodies, and a loss of the supraoesophageal brain commissure.
Results
In this study we conducted a detailed expression analysis of Hbn in later developmental stages. In the larval brain, Hbn is expressed in all type II lineages and the optic lobes, including the medulla and lobula plug. The gene is expressed in the cortex of the medulla and the lobula rim in the adult brain. We generated a new hbnKOGal4 enhancer trap strain by reintegrating Gal4 in the hbn locus through gene targeting, which reflects the complete hbn expression during development. Eight different enhancer-Gal4 strains covering 12 kb upstream of hbn, the two large introns and 5 kb downstream of the gene, were established and hbn expression was investigated. We characterized several enhancers that drive expression in specific areas of the brain throughout development, from embryo to the adulthood. Finally, we generated deletions of four of these enhancer regions through gene targeting and analysed their effects on the expression and function of hbn.
Conclusion
The complex expression of Hbn in the developing brain is regulated by several specific enhancers within the hbn locus. Each enhancer fragment drives hbn expression in several specific cell lineages, and with largely overlapping patterns, suggesting the presence of shadow enhancers and enhancer redundancy. Specific enhancer deletion strains generated by gene targeting display developmental defects in the brain. This analysis opens an avenue for a deeper analysis of hbn regulatory elements in the future.
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