The abnormal spindle protein is required for germ cell mitosis and oocyte differentiation during Drosophila oogenesis

Drosophila oocyte proteome composition covaries with female mating status

Oocyte composition can directly influence offspring fitness, particularly in oviparous species such as most insects, where it is the primary form of parental investment. Oocyte production is also energetically costly, dependent on female condition and responsive to external cues. Here, we investigated whether mating influences mature oocyte composition in Drosophila melanogaster using a quantitative proteomic approach. Our analyses robustly identified 4,485 oocyte proteins and revealed that stage-14 oocytes from mated females differed significantly in protein composition relative to oocytes from unmated females. Proteins forming a highly interconnected network enriched for translational machinery and transmembrane proteins were increased in oocytes from mated females, including calcium binding and transport proteins. This mating-induced modulation of oocyte maturation was also significantly associated with proteome changes that are known to be triggered by egg activation. We propose that these compositional changes are likely to have fitness consequences and adaptive implications given the importance of oocyte protein composition, rather than active gene expression, to the maternal-to-zygotic transition and early embryogenesis.

Mutation rate estimation for 15 autosomal STR loci in a large population from Mainland China

STR, short tandem repeats, are well known as a type of powerful genetic marker and widely used in studying human population genetics. Compared with the conventional genetic markers, the mutation rate of STR is higher. Additionally, the mutations of STR loci do not lead to genetic inconsistencies between the genotypes of parents and children; therefore, the analysis of STR mutation is more suited to assess the population mutation. In this study, we focused on 15 autosomal STR loci. DNA samples from a total of 42,416 unrelated healthy individuals (19,037 trios) from the population of Mainland China collected between Jan 2012 and May 2014 were successfully investigated. In our study, the allele frequencies, paternal mutation rates, maternal mutation rates and average mutation rates were detected. Furthermore, we also investigated the relationship between paternal ages, maternal ages, area, the time of pregnancy and average mutation rate. We found that the paternal mutation rate was higher than the maternal mutation rate and the paternal, maternal, and average mutation rates had a positive correlation with paternal age, maternal age and the time of pregnancy respectively. Additionally, the average mutation rate of coastal areas was higher than that of inland areas.

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15 autosomal STR loci were analyzed in a large scale population in Mainland China.

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With increases of repeat units the event of loss is more than that of gain.

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The paternal mutation rate is higher than the maternal mutation rate.

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There is a positive correlation between mutation rates and age and pregnancy time.

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The average mutation rates of coastal areas are higher than that of inland areas.

Mutations in mouse Aspm (abnormal spindle-like microcephaly associated) cause not only microcephaly but also major defects in the germline

Mutations in ASPM (abnormal spindle-like microcephaly associated) cause primary microcephaly in humans, a disorder characterized by a major reduction in brain size in the apparent absence of nonneurological anomalies. The function of the Aspm protein in neural progenitor cell expansion, as well as its localization to the mitotic spindle and midbody, suggest that it regulates brain development by a cell division-related mechanism. Furthermore, evidence that positive selection affected ASPM during primate evolution has led to suggestions that such a function changed during primate evolution. Here, we report that in Aspm mutant mice, truncated Aspm proteins similar to those causing microcephaly in humans fail to localize to the midbody during M-phase and cause mild microcephaly. A human ASPM transgene rescues this phenotype but, interestingly, does not cause a gain of function. Strikingly, truncated Aspm proteins also cause a massive loss of germ cells, resulting in a severe reduction in testis and ovary size accompanied by reduced fertility. These germline effects, too, are fully rescued by the human ASPM transgene, indicating that ASPM is functionally similar in mice and humans. Our findings broaden the spectrum of phenotypic effects of ASPM mutations and raise the possibility that positive selection of ASPM during primate evolution reflects its function in the germline.

Deadlock, a novel protein of Drosophila, is required for germline maintenance, fusome morphogenesis and axial patterning in oogenesis and associates with centrosomes in the early embryo

The deadlock gene is required for a number of key developmental events in Drosophila oogenesis. Females homozygous for mutations in the deadlock gene lay few eggs and those exhibit severe patterning defects along both the anterior-posterior and dorsal-ventral axis. In this study, we analyzed eggs and ovaries from deadlock mutants and determined that deadlock is required for germline maintenance, stability of mitotic spindles, localization of patterning determinants, oocyte growth and fusome biogenesis in males and females. Deadlock encodes a novel protein which colocalizes with the oocyte nucleus at midstages of oogenesis and with the centrosomes of early embryos. Our genetic and immunohistological experiments point to a role for Deadlock in microtubule function during oogenesis.

Cytoskeletal genes regulating brain size

One of the most notable trends in human evolution is the dramatic increase in brain size that has occurred in the great ape clade, culminating in humans. Of particular interest is the vast expanse of the cerebral cortex, which is believed to have resulted in our ability to perform higher cognitive functions. Recent investigations of congenital microcephaly in humans have resulted in the identification of several genes that non-redundantly and specifically influence mammalian brain size. These genes appear to affect neural progenitor cell number through microtubular organisation at the centrosome.

Evolution of primary microcephaly genes and the enlargement of primate brains

Brain size, in relation to body size, has varied markedly during the evolution of mammals. In particular, a large cerebral cortex is a feature that distinguishes humans from our fellow primates. Such anatomical changes must have a basis in genetic alterations, but the molecular processes involved have yet to be defined. However, recent advances from the cloning of two human disease genes promise to make inroads in this important area. Microcephalin (MCPH1) and Abnormal spindle-like microcephaly associated (ASPM) are genes mutated in primary microcephaly, a human neurodevelopmental disorder. In this 'atavistic' condition, brain size is reduced in volume to a size comparable with that of early hominids. Hence, it has been proposed that these genes evolved adaptively with increasing primate brain size. Subsequent studies have lent weight to this hypothesis by showing that both genes have undergone positive selection during great ape evolution. Further functional characterisation of their proteins will contribute to an understanding of the molecular and evolutionary processes that have determined human brain size.

Duplication and positive selection among hominin-specific PRAME genes

Background

The physiological and phenotypic differences between human and chimpanzee are largely specified by our genomic differences. We have been particularly interested in recent duplications in the human genome as examples of relatively large-scale changes to our genome. We performed an in-depth evolutionary analysis of a region of chromosome 1, which is copy number polymorphic among humans, and that contains at least 32 PRAME (Preferentially expressed antigen of melanoma) genes and pseudogenes. PRAME-like genes are expressed in the testis and in a large number of tumours, and are thought to possess roles in spermatogenesis and oogenesis.

Results

Using nucleotide substitution rate estimates for exons and introns, we show that two large segmental duplications, of six and seven human PRAME genes respectively, occurred in the last 3 million years. These duplicated genes are thus hominin-specific, having arisen in our genome since the divergence from chimpanzee. This cluster of PRAME genes appears to have arisen initially from a translocation approximately 95–85 million years ago. We identified multiple sites within human or mouse PRAME sequences which exhibit strong evidence of positive selection. These form a pronounced cluster on one face of the predicted PRAME protein structure.

Conclusion

We predict that PRAME genes evolved adaptively due to strong competition between rapidly-dividing cells during spermatogenesis and oogenesis. We suggest that as PRAME gene copy number is polymorphic among individuals, positive selection of PRAME alleles may still prevail within the human population.