The sex-linked Notch locus plays an important role in
embryogenesis and determination of many adult structures of the
fruit fly, Drosophila melanogaster. Mutation at this locus can
cause lethality in embryonic or later stages, as well as morphological
abnormalities of the adult eyes, wings, bristles and legs.
Alleles of the Notch locus can be broadly grouped into three
classes: 1) recessive lethal Notch (N) alleles, which may be
deficiencies or point mutations, 2) Abruptex (Ax) alleles, which
are probably point mutations and may be either lethal or viable,
and 3) viable recessive alleles with visible phenotypes, which
affect a variety of traits and are point mutations. The present
investigation was initiated with a view to understanding the
relationships between N and Ax alleles and the nature of their
role in development, and has consisted mainly of the following
approaches: 1) an examination of the phenotypes of certain
unusual N alleles and the phenotypic responses to alteration of
the dosage of these alleles in relation to wild-type (N+), 2) an
examination of the interaction of Ax alleles with N alleles and
with one another, and 3) developmental studies of the conditional
(temperature-sensitive) phenotypes associated with certain Notch-locus
genotypes.
The results of the N-allele dosage study indicate that a
single mutation in the Notch locus can affect different functions
associated with this locus in fundamentally different ways. Depending
on the genotype and phenotype examined, the responses of
various N alleles to dosage changes suggest that mutation at the
Notch locus may result in reduced, increased or novel activity
at the locus.
Four ethyl methanesulfonate-induced Ax alleles have been
examined, none of which is cytologically abnormal in salivary
gland chromosome preparations, and at least three of which map
within the Notch locus. Depending on culture conditions and
the alleles involved, Ax/N heteroallelic combinations may be
viable or lethal. All Ax/N combinations studied exhibited less
severe Abruptex phenotypes (bristle loss and wing vein gapping)
than the respective Ax/Ax homozygotes. However, the Ax alleles
differed from one another in their effects on the wing nicking
of the N alleles, in that the viable allele Ax9B2 and the semi-
lethal allele AxE1 both suppressed wing nicking, whereas the two
viable alleles AxE2 and AX16172 both enhanced wing nicking.
Furthermore, heteroallelic combinations of Ax alleles which
affected nicking in different direction, were lethal (AxE1/AxE2,
AxE1/Ax16172, Ax9B2/Ax16172), whereas combinations of Ax alleles
with similar effects on nicking were viable (AxE1/Ax9B2, AxE2/
Ax16172).
The temperature-shift experiments have revealed an interesting
pattern of temperature-sensitive periods (TSPs) for lethality
or adult morphological abnormalities associated with various
Notch-locus genotypes. TSPs for lethality may be monophasic
occurring in the embryo (N60g11/N6g11;Dp51b7), or the second
larval instar (Ax16172/n264-40), or they may be polyphasic, occurring
in embryo, larval and pupal stages (N264-103/fano). On the
other hand, the TSPs for all the adult morphological abnormalities
examined occur during the third larval instar, including
rough eyes and wing nicking
(N60gll/+,N264-103/spl), leg segment
fusion (N264-103/+, N264-103/spl), wing vein gapping (Ax16172/+)
and disturbance of bristle numbers (N264-103/spl, Ax16172/+).
Several molecular models are discussed in relation to the
observations on N-allele dosage and interactions of the Ax and N
alleles. The results are consistent with the hypothesis that the
Notch locus is a regulator gene influencing many developmental
processes, that mutations can affect the activity either of the
entire gene or of various parts of the gene individually, and
that N and Ax mutations usually affect this regulatory system in opposite
ways from one another. / Science, Faculty of / Zoology, Department of / Graduate
| Identifer | oai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/42117 |
| Date | January 1971 |
| Creators | Foster, Geoffrey George |
| Publisher | University of British Columbia |
| Source Sets | University of British Columbia |
| Language | English |
| Detected Language | English |
| Type | Text, Thesis/Dissertation |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
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