Allocation and specification of the genital disc precursor cells in Drosophila

Abstract

The adult structures of Drosophila melanogaster are derived from larval imaginal discs, which originate as clusters of cells within the embryonic ectoderm. The genital imaginal disc is composed of three primordia (female genital, male genital, and anal primordia) that originate from the embryonic tail segments A8, A9, and A10, respectively, and produce the sexually dimorphic genitalia and analia. We show that the genital disc precursor cells (GDPCs) are first detectable during mid-embryogenesis as a 22-cell cluster in the ventral epidermis. Analysis of mutant and double mutant phenotypes of embryonic patterning genes in the GDPCs, together with their expression patterns in these cells, revealed the following with respect to the origins and specification of the GDPCs. The allocation of the GDPCs from the ventral epidermis requires the function of ventral patterning genes, including the EGF receptor and the spitz group of genes. The ventral localization of the GDPCs is further restricted by the action of dorsal patterning genes. Along the anterior-posterior axis, several segment polarity genes (wingless, engrailed, hedgehog, and patched) are required for the proper allocation of the GDPCs. These segment polarity genes are expressed in some, but not all of the GDPCs, indicating that anterior and posterior compartments are not fully established in the GDPCs. In addition, we found that the three primordia of the larval genital disc have already been specified in the GDPCs by the coordinated actions of the homeotic (Hox) genes, abdominal-A, Abdominal-B, and caudal. By identifying how these different patterning networks regulate the allocation and primordial organization of the 22 embryonic precursors of the compound genital disc, we demonstrate that at least some of the organization of the larval disc originates as positional information in the embryo, thus providing a context for further studies on the development of the genital disc.

Both jnk and apoptosis pathways regulate growth and terminalia rotation during Drosophila genital disc development

“…The overgrowth split the GA and T8 (Fig. 6 G-G''), so death was also prevented outside the A10 and should only affect en cells (Chen et al, 2005). Ectopic expression of P35 or DIAP1 resulted in adult males with rotated terminalia and overgrowth as well (Table 1).…”

“…6 L-L'), and this overgrowth included cells of other primordia (Fig. 6L', white arrowhead), which might be en cells (Chen et al, 2005) or are en A10 undead migratory cells (Martín et al, in press). …”

“…The GFP-positive cells within the GA and AP exhibited low fluorescence, which is consistent with the low expression of the driver in en cells. The inhibition of death in the en region outside A8 can be explained by the previous proposal that the en domain originates from one primordium of cells (Chen et al, 2005). Alternatively, Martín et al (in press) reported that en cells acquire migratory properties when their death is prevented (undead cells).…”

“…However, its morphology and growth characteristics differ in males and females. The genital disc arises from the invagination and fusion of ventral cells from the eighth (A8), ninth (A9) and tenth (A10) abdominal segments (reviewed in Sánchez and Guerrero, 2001;Estrada et al, 2003, Chen et al, 2005. Although originating from the same ventral posterior segments, the precursor cells develop into sexually dimorphic structures, in accordance with the sex-determination genes.…”

“…The A10 segment in both sexes gives rise to the analia and the hindgut; however, the analias are dimorphic (reviewed in Sánchez and Guerrero, 2001;Estrada et al, 2003). In contrast to other imaginal cells, part of the domain of cells expressing engrailed (en) is not established during the embryonic stage (Casares et al, 1997;Chen et al, 2005). Finally, during male development, the A8 cells direct a dextral 360° rotation (Gleichauf, 1936, Spéder et al, 2006.…”