The analysis of consequences resulting after experimental elimination of gene function has been and will continue to be an extremely successful strategy in biological research. Mutational elimination of gene function has been widely used in the fly Drosophila melanogaster. RNA interference is used extensively as well. In the fly, exceptionally precise temporal and spatial control over elimination of gene function can be achieved in combination with sophisticated transgenic approaches and clonal analyses. However, the methods that act at the gene and transcript level cannot eliminate protein products which are already present at the time when mutant cells are generated or RNA interference is started. Targeted inducible protein degradation is therefore of considerable interest for controlled rapid elimination of gene function. To this end, a degradation system was developed in yeast exploiting TIR1, a plant F box protein, which can recruit proteins with an auxin-inducible degron to an E3 ubiquitin ligase complex, but only in the presence of the phytohormone auxin. Here we demonstrate that the auxin-inducible degradation system functions efficiently also in Drosophila melanogaster. Neither auxin nor TIR1 expression have obvious toxic effects in this organism, and in combination they result in rapid degradation of a target protein fused to the auxin-inducible degron.

The first meiotic division reduces genome ploidy. This requires pairing of homologous chromosomes into bivalents that can be bi-oriented within the spindle during prometaphase I. Thereafter, pairing is abolished during late metaphase I, and univalents are segregated apart onto opposite spindle poles during anaphase I. In contrast to canonical meiosis, homologous chromosome pairing does not include the formation of a synaptonemal complex and of cross-overs in spermatocytes of Drosophila melanogaster . The alternative pairing mode in these cells depends on mnm and snm . These genes are required exclusively in spermatocytes specifically for successful conjunction of chromosomes into bivalents. Available evidence suggests that MNM and SNM might be part of a physical linkage that directly conjoins chromosomes. Here this notion was analyzed further. Temporal variation in delivery of mnm and snm function was realized by combining various transgenes with null mutant backgrounds. The observed phenotypic consequences provide strong evidence that MNM and SNM contribute directly to chromosome linkage. Premature elimination of these proteins results in precocious bivalent splitting. Delayed provision results in partial conjunction defects that are more pronounced in autosomal bivalents compared to the sex chromosome bivalent. Overall, our findings suggest that MNM and SNM cannot re-establish pairing of chromosomes into bivalents if provided after a chromosome-specific time point of no return. When delivered before this time point, they fortify preformed linkages in order to preclude premature bivalent splitting by the disruptive forces that drive chromosome territory formation during spermatocyte maturation and chromosome condensation during entry into meiosis I.

Submicroscopic chromosomal anomalies play an important role in the aetiology of intellectual disability (ID) and have been shown to account for up to 10% of non-syndromic forms. We present a family with two affected boys compatible with X-linked inheritance of a phenotype of severe neurodevelopmental disorder co-segregating with a deletion in Xp22.11 exclusively containing the PTCHD1 gene. Although the exact function of this gene is unknown to date, the structural overlap of its encoded patched domain-containing protein 1, the transmembrane protein involved in the sonic hedgehog pathway, and its expression in human cortex and cerebellum as well as in mice and drosophila brain suggests a causative role of its nullisomy in the developmental phenotype of our family. Our findings support the recent notions that PTCHD1 may play a role in X-linked intellectual disability (XLID) and autism disorders.

Split-hand/foot malformation (SHFM) is a limb malformation affecting the central rays of the hands and/or feet. Isolated SHFM occurs within families but more often sporadically. Since most families with more than one patient show dominant inheritance with reduced penetrance, sporadic SHFM is generally considered to be due to dominantly inherited new mutations. Recently, recessive inheritance of SHFM was proposed in a highly consanguineous family with a homozygous missense mutation in WNT10B. Nevertheless, the assumption of a second locus was necessary to explain the observed phenotypes in this family. To date, no other family and no case of sporadic SHFM with WNT10B mutations are known. By examining WNT10B in a patient with sporadic SHFM, we identified a homozygous 4-bp duplication resulting in a premature termination codon. Nine heterozygous relatives show no sign of SHFM. These findings have profound implications for genetic counseling. Obviously, sporadic SHFM may show recessive rather than dominant inheritance resulting in a 25% recurrence risk for sibs instead of a very low-recurrence risk as generally presumed. Likewise, there is a very low-recurrence risk for offspring of patients (unless there is consanguinity) instead of an estimated risk between 30% and 50%. It can be concluded that sporadic SHFM is not always a dominant trait. To determine the recurrence risk, patients affected with sporadic SHFM should be tested for mutations in WNT10B.

Spatially controlled release of sister chromatid cohesion during progression through the meiotic divisions is of paramount importance for error-free chromosome segregation during meiosis. Cohesion is mediated by the cohesin protein complex and cleavage of one of its subunits by the endoprotease separase removes cohesin first from chromosome arms during exit from meiosis I and later from the pericentromeric region during exit from meiosis II. At the onset of the meiotic divisions, cohesin has also been proposed to be present within the centromeric region for the unification of sister centromeres into a single functional entity, allowing bipolar orientation of paired homologs within the meiosis I spindle. Separase-mediated removal of centromeric cohesin during exit from meiosis I might explain sister centromere individualization which is essential for subsequent biorientation of sister centromeres during meiosis II. To characterize a potential involvement of separase in sister centromere individualization before meiosis II, we have studied meiosis in Drosophila melanogaster males where homologs are not paired in the canonical manner. Meiosis does not include meiotic recombination and synaptonemal complex formation in these males. Instead, an alternative homolog conjunction system keeps homologous chromosomes in pairs. Using independent strategies for spermatocyte-specific depletion of separase complex subunits in combination with time-lapse imaging, we demonstrate that separase is required for the inactivation of this alternative conjunction at anaphase I onset. Mutations that abolish alternative homolog conjunction therefore result in random segregation of univalents during meiosis I also after separase depletion. Interestingly, these univalents become bioriented during meiosis II, suggesting that sister centromere individualization before meiosis II does not require separase.