Molecular analysis of the deletion mutants in the E homeotic complex of the silkworm Bombyx mori.

The E loci in Bombyx mori are expected to contain a homeotic gene complex specifying the identities of the larval abdominal segments. However, the molecular structure of this complex remains to be determined. We have started to analyze the structural changes in the E complex mutations. We used three newly isolated Bombyx homeobox genes as probes. These genes are probably homologues of the Ultrabithorax (Ubx), abdominal-A (abd-A) and Abdominal-B (Abd-B) in the Drosophila bithorax complex, because the amino-acid sequences of the homeobox regions in these Bombyx genes are almost identical to those of Drosophila genes. We found that the Bombyx Ubx and abd-A genes are deleted in the EN chromosome, and the Bombyx abd-A gene is deleted in the ECa chromosome. From these results, we conclude that the Bombyx E complex consists of the Ubx, abd-A and possibly Abd-B genes, which may play similar roles to their homologues in the Drosophila bithorax complex.     

Control of the expression of the bithorax complex genes abdominal-A and abdominal-B by cis-regulatory regions in Drosophila embryos.

The abdominal-A (abd-A) and Abdominal-B (Abd-B) genes of the bithorax complex (BX-C) specify the identity of most of the Drosophila abdomen. Six different classes of infraabdominal (iab) mutations within the BX-C transform a subset of the parasegments affected by the lack of these two genes. It is thought that these mutations define parasegmental cis-regulatory regions that control the expression of abd-A and Abd-B. By staining embryos mutant for different iab mutations with anti-abd-A and anti-Abd-B antibodies I show here that the expression of Abd-B (and probably also abd-A) exhibit a parasegmental regulation. I have also studied the significance of the chromosomal order of parasegmental iab regulatory sequences, and the possible presence of chromosomal 'boundaries' between them, by looking at the expression of abd-A and Abd-B in embryos carrying the Uab and Mcp mutations. These data are discussed in the light of models of parasegmental-specific regulatory regions within the BX-C.     

应用RNA原位杂交技术研究马尾松针叶中银松素合酶的基因表达

以马尾松（Pinus massoniana Lamb．）银松素合酶（PS）基因为模板,体外转录合成带地高辛标记的反义RNA全长及特异探针,并用这2个探针与马尾松针叶组织石蜡切片进行原位杂交,研究该基因在马尾松针叶中的表达特性以及外界诱导因素对该基因表达的调节特性。结果表明,该基因的转录表达主要集中在针叶的韧皮部;紫外线照射和酵母提取液处理均可使该基因的转录水平明显增加。     

Ectopic expression of UBX and ABD-B proteins during Drosophila embryogenesis: competition, not a functional hierarchy, explains phenotypic suppression.

The Abdominal-B (Abd-B) gene, a member of the bithorax complex (BX-C), specifies the identities of parasegments (PS) 10-14 in Drosophila. Abd-B codes for two structurally related homeodomain proteins, ABD-B m and ABD-B r, that are expressed in PS10-13 and PS14-15, respectively. Although ABD-B m and r proteins have distinct developmental functions, ectopic expression of either protein during embryogenesis induces the development of filzk?rper and associated spiracular hairs, structures normally located in PS13, at ectopic sites in the larval thorax and abdomen. These results suggest that other parasegmental differences contribute to the phenotype specified by ABD-B r activity in PS14. Both ABD-B m and r repress the expression of other homeotic genes, such as Ubx and abd-A, in PS10-14. However, the importance of these and other cross-regulatory interactions among homeotic genes has been questioned. Since ectopic UBX protein apparently failed to transform abdominal segments, González-Reyes et al. (González-Reyes, A., Urquía, N., Gehring, W.J., Struhl, G. and Morata, G. (1990). Nature 344, 78-80) proposed a functional hierarchy in which ABD-A and ABD-B activities override UBX activity. We tested this model by expressing UBX and ABD-B m proteins ectopically in wild-type and BX-C-deficient embryos. Ectopic ABD-B m does not prevent transformations induced by ectopic UBX. Instead, ectopic UBX and ABD-B m proteins compete for the specification of segmental identities in a dose-dependent fashion. Our results support a quantitative competition among the homeotic proteins rather than the existence of a strict functional hierarchy. Therefore, we suggest that cross-regulatory interactions are not irrelevant but are important for repressing the expression of competing homeotic proteins. To explain the apparent failure of ectopic UBX to transform the abdominal segments, we expressed UBX at different times during embryonic development. Our results show that ectopic UBX affects abdominal cuticular identities if expressed during early stages of embryogenesis. In later embryonic stages, abdominal segments become resistant to transformation by ectopic UBX while thoracic segments remain susceptible. Head segments also show a similar stage-dependent susceptibility to transformation by ectopic UBX in early embryogenesis but become resistant in later stages. These results suggest that abdominal and head identities are determined earlier than are thoracic identities.     

The Fab-8 boundary defines the distal limit of the bithorax complex iab-7 domain and insulates iab-7 from initiation elements and a PRE in the adjacent iab-8 domain

The Drosophila bithorax complex Abdominal-B (Abd-B) gene specifies parasegmental identity at the posterior end of the fly. The specific pattern of Abd-B expression in each parasegment (PS) determines its identity and, in PS10-13, Abd-B expression is controlled by four parasegment-specific cis-regulatory domains, iab-5 to iab-8, respectively. In order to properly determine parasegmental identity, these four cis-regulatory domains must function autonomously during both the initiation and maintenance phases of BX-C regulation. The studies reported here demonstrate that the (centromere) distal end of iab-7 domain is delimited by the Fab-8 boundary. Initiators that specify PS12 identity are located on the proximal iab-7 side of Fab-8, while initiators that specify PS13 identity are located on the distal side of Fab-8, in iab-8. We use transgene assays to demonstrate that Fab-8 has enhancer blocking activity and that it can insulate reporter constructs from the regulatory action of the iab-7 and iab-8 initiators. We also show that the Fab-8 boundary defines the realm of action of a nearby iab-8 Polycomb Response Element, preventing this element from ectopically silencing the adjacent domain. Finally, we demonstrate that the insulating activity of the Fab-8 boundary in BX-C is absolutely essential for the proper specification of parasegmental identity by the iab-7 and iab-8 cis-regulatory domains. Fab-8 together with the previously identified Fab-7 boundary delimit the first genetically defined higher order domain in a multicellular eukaryote.