Effects of mutations at the stambh A locus of Drosophila melanogaster.

We report novel findings on the cytogenetic location, functional complexity and maternal and germline roles of the stambh A locus of Drosophila melanogaster. stmA is localized to polytene bands 44D1.2 on 2R. stmA mutations are of two types: temperature-sensitive (ts) adult and larval paralytic or unconditional embryonic or larval lethal. Twelve alleles reported in this study fall into two intragenic complementing groups suggesting that stmA is a complex locus with more than one functional domain. Some unconditional embryonic lethal alleles show a 'neurogenic' phenotype of cuticle loss accompanied by neural hypertrophy. It is shown that embryos of ts paralytic alleles also show mild neural hypertrophy at permissive temperatures while short exposure to heat induces severe cuticle loss in these embryos. stmA exerts a maternal influence over heat-induced cuticle loss. Unconditional embryonic lethal alleles of stmA are also germline lethal.

A female sterile embryonic lethal in the maternally haplo-insufficient 21 B8.C1-21 C8.D1 genomic region of Drosophila melanogaster.

Maternal hemizygosity of the 21 B8.C1-21 C8.D1 aristaless region of chromosome 2L of Drosophila melanogaster leads to high levels of embryonic mortality from the cross of Df(2L) al/+ females x +/+ males. The 21 B8.C1-21 C8.D1 polytene section therefore carries maternally active genes essential for embryogenesis. Selective screening for female sterile mutants against Df(2L) al yielded six alleles of a new female sterile embryonic lethal. This confirms the assumption that genomic regions that are maternally haplo-insufficient for normal embryogenesis house maternally active gene(s). It also demonstrates that mutational analysis of similar genomic regions can identify maternally acting embryonic lethal loci which escaped detection in spite of extensive screening experiments.

Phenotypes of lethal alleles of the recessive temperature sensitive paralytic mutant stambh A of Drosophila melanogaster suggest its neurogenic function.

The mutant stambhA1 (2-56.8) of Drosophila melanogaster was identified as a reversible temperature sensitive adult and larval paralytic. We have (i) isolated and analysed phenotypes of one new homozygous viable paralytic allele and two recessive unconditional embryonic lethal alleles of stmA and (ii) studied the interaction of the viable paralytic alleles with ts paralytic mutants napts1 (2-55.2) and parats1 (1-53.9). The homozygous viable paralytic alleles stmA2 and stmA1 are semi dominant neomorphs. The lethal alleles stmA12 and stmA7 appear to be amorphs. Unhatched embryos expressing lethal stmA alleles showed hypotrophy of the anterior dorsal cuticle overlying the brain with a concomitant hypertrophy of the anterior dorsal neurogenic region (the brain). The ventral cuticle was poorly differentiated, and the ventral nerve chord showed mild hypertrophy and poor organisation. The epidermal cells in 12-13 h old embryos did not show the normal palisade layer arrangement. These phenotypes are similar to mutant phenotypes of the neurogenic class of genes whose wild type functions are necessary for intercellular communication. The alleles stmA1 and stmA2 do not appear to interact with the paralytic mutants napts1 or parats1 in double mutant combinations. On the basis of our results it is proposed that stmA may belong to the neurogenic class of genes.