The recombinational analysis of aberrations and the position of the Notch locus on the polytene chromosome of Drosophila

Abstract

The recombinational analysis of heterozygotes for a point-mutant N and a deficiency N suggests that the map region approximated by the interval fa to nd2 is at the right edge of salivary band 3C7 or in the interband to the right. The map region N55ell to fa can be anywhere between the left-interband and the right edge of 3C7. We discovered that small inversions also can be used in the recombinational analysis, and the inversion data support the conclusions already described. The reactivation of latent mutability in a Notch inversion resulted in reinversion of the original aberration, followed by reversion of N to N+. From the same Notch inversion, we isolated a spontaneous deficiency superimposed upon the original aberration, which supported our hypothesis that two of our w to N deficiencies probably originated as deficiencies superimposed upon inversions.

The role of insulator elements in large-scale chromatin structure in interphase

“…The facet-strawberry (fa swb ) deletion in the interband between bands 3C6 and 3C7 causes the two bands to fuse, with the interband disappearing [52]. The fa swb phenotype includes a rough, variably glossy eye, thought to be due to PEV affecting the nearby Notch promoter.…”

Molecular cloning of Notch, a locus affecting neurogenesis in Drosophila melanogaster.

“…We have begun with the analysis of Notch, which is best understood, genetically and phenotypically (4,5). The Notch locus, symbolized N, is located at band 3C7 of the salivary gland chromosomes and is genetically defined by an array of mutations that, when heterozygous, yield a dominant phenotype consisting of variably notched wings, thickened wing veins, and minor bristle abnormalities (6).…”

Functional analysis of Drosophila polytene chromosomes decompacted unit: the interband

“…Multiple immunolocalization experiments have mapped protein components of different Drosophila insulators to interbands or band-interband borders, leading to the idea that insulators are essential for differential compaction of interphase chromosomes. Consistent with this idea, the 3C6/C7 interband region was shown to harbor a functional insulator (Vazquez and Schedl 2000) and the presence of this insulator element appeared to be crucial for interband morphology (Welshons and Keppy 1981). Both 3C6/C7 and 61C7/C8 regions show extremely low if any transcriptional activity in salivary gland as no long transcripts could be detected by northern-blot analysis (Demakov et al 2004) or by real-time PCR (E. Z. Kvon, unpublished data).…”

“…When a critical part of this insulator is removed in facet-strawberry (fa swb ) deletion (Fig. 1a) the 3C6/C7 interband disappears (Welshons and Keppy 1981), suggesting that insulator activity may be important for shielding the region from condensation by neighboring chromatin.…”