Copb2 is essential for embryogenesis and hypomorphic mutations cause human microcephaly

Primary microcephaly is a congenital brain malformation characterized by a head circumference less than three standard deviations below the mean for age and sex and results in moderate to severe mental deficiencies and decreased lifespan. We recently studied two children with primary microcephaly in an otherwise unaffected family. Exome sequencing identified an autosomal recessive mutation leading to an amino acid substitution in a WD40 domain of the highly conserved Coatomer Protein Complex, Subunit Beta 2 (COPB2). To study the role of Copb2 in neural development, we utilized genome-editing technology to generate an allelic series in the mouse. Two independent null alleles revealed that Copb2 is essential for early stages of embryogenesis. Mice homozygous for the patient variant (Copb2R254C/R254C) appear to have a grossly normal phenotype, likely due to differences in corticogenesis between the two species. Strikingly, mice heterozygous for the patient mutation and a null allele (Copb2R254C/Zfn) show a severe perinatal phenotype including low neonatal weight, significantly increased apoptosis in the brain, and death within the first week of life. Immunostaining of the Copb2R254C/Zfnbrain revealed a reduction in layer V (CTIP2+) neurons, while the overall cell density of the cortex is unchanged. Moreover, neurospheres derived from animals with Copb2 variants grew less than control. These results identify a general requirement for COPB2 in embryogenesis and a specific role in corticogenesis. We further demonstrate the utility of CRISPR-Cas9 generated mouse models in the study of potential pathogenicity of variants of potential clinical interest.

A heterozygous mutation in tubulin, beta 2B ( Tubb2b ) causes cognitive deficits and hippocampal disorganization

Development of the mammalian forebrain requires a significant contribution from tubulin proteins to physically facilitate both the large number of mitoses in the neurogenic brain (in the form of mitotic spindles) as well as support cellular scaffolds to guide radial migration (radial glial neuroblasts). Recent studies have identified a number of mutations in human tubulin genes affecting the forebrain, including TUBB2B . We previously identified a mouse mutation in Tubb2b and we show here that mice heterozygous for this missense mutation in Tubb2b have significant cognitive defects in spatial learning and memory. We further showed reduced hippocampal long-term potentiation consistent with these defects. In addition to the behavioural and physiological deficits, we show here abnormal hippocampal morphology. Taken together, these phenotypes suggest that heterozygous mutations in tubulin genes result in cognitive deficits not previously appreciated. This has implications for design and interpretation of genetic testing for humans with intellectual disability disorders.

Differential expression of heat shock protein genes and their splice variants in bovine preimplantation embryos

Heat shock proteins (HSP) are among the first proteins produced during embryonic development and are crucial to cell function; their activities include folding, unfolding, transport, and localization of proteins and differentiation and regulation of the embryonic cell cycle. Although HSP have been extensively studied in humans and mice, limited information exists on the roles of these genes in bovine embryos. As such, the objectives of this study were to profile the expression of HSP and their splice variants in bovine embryos (degenerates vs. blastocysts) and to carry out association analysis with fertility traits. Quantitative real time PCR analysis revealed differences in expression that ranged from 1.5- to 7.6-fold in degenerate embryos compared with blastocysts. Interestingly, all members of the HSP40 family were found to be upregulated in degenerate embryos. Analysis of current bovine Ensembl data showed that 13 HSP genes have 1 transcript each, 2 genes have 2 transcripts each, and 2 have 3 transcripts each. Some splice variants show differential expression between degenerate embryos and blastocysts, whereas others were not expressed at all in embryos, which implies different functions of these transcripts in embryonic development. The most significant differentially expressed genes were further investigated for association with fertility and development traits. Single nucleotide polymorphisms in DNAJC15 and DNAJC27 were found to be associated with blastocyst rate and fertilization rate, respectively. Collectively, the roles of HSP in fertilization and early development of cattle embryos are important.

Short communication: expression and alternative splicing of POU1F1 pathway genes in preimplantation bovine embryos

Early embryo loss is a major contributing factor to cow infertility and that 70 to 80% of this loss occurs between d 8 and 16 postfertilization. However, little is known about the molecular mechanisms and the nature of genes involved in normal and abnormal embryonic development. Moreover, information is limited on the contributions of the genomes of dams and of embryos to the development and survival of preimplantation embryos. We hypothesized that proper gene expression level in the developing embryo is essential for embryo survival and pregnancy success. As such, the characterization of expression profiles in early embryos could lead to a better understanding of the mechanisms involved in normal and abnormal embryo development. To test this hypothesis, 2 d-8 embryo populations (degenerate embryos and blastocysts) that differed in morphology and developmental status were investigated. Expression levels of POU1F1 pathway genes were estimated in 4 sets of biological replicate pools of degenerate embryos and blastocysts. The OPN and STAT5A genes were found to be upregulated in degenerate embryos compared with blastocysts, whereas STAT5B showed similar expression levels in both embryo groups. Analysis of splice variants of OPN and STAT5A revealed expression patterns different from the total expression values of these genes. As such, measuring expression of individual transcripts should be considered in gene expression studies.

Absorptive capacity as a guiding concept for effective public sector management and conservation of freshwater ecosystems

The ability of an organisation to recognise the value of new external information, acquire it, assimilate it, transform, and exploit it, namely its absorptive capacity (AC), has been much researched in the context of commercial organisations and even applied to national innovation. This paper considers four key AC-related concepts and their relevance to public sector organisations with mandates to manage and conserve freshwater ecosystems for the common good. The concepts are the importance of in-house prior related knowledge, the importance of informal knowledge transfer, the need for motivation and intensity of effort, and the importance of gatekeepers. These concepts are used to synthesise guidance for a way forward in respect of such freshwater management and conservation, using the imminent release of a specific scientific conservation planning and management tool in South Africa as a case study. The tool comprises a comprehensive series of maps that depict national freshwater ecosystem priority areas for South Africa. Insights for implementing agencies relate to maintaining an internal science, rather than research capacity; making unpublished and especially tacit knowledge available through informal knowledge transfer; not underestimating the importance of intensity of effort required to create AC, driven by focussed motivation; and the potential use of a gatekeeper at national level (external to the implementing organisations), possibly playing a more general 'bridging' role, and multiple internal (organisational) gatekeepers playing the more limited role of 'knowledge translators'. The role of AC as a unifying framework is also proposed.

Measuring central executive functioning: what's in a reading span?

Although variations of Daneman and Carpenter's (1980) Reading Span Test (RST) have seen increasing use in both cognitive and neuropsychological research, the specific mental operations involved in performing it remain unclear. We tested 80 undergraduates to examine the extent to which speed of processing, manipulation capacity, and susceptibility to interference contributed to RST performance. The results suggest that, rather than unitary central executive or processing speed functions underlying RST performance, at least two factors, manipulation capacity and susceptibility to interference, underlie the task. Further study of RST operations may lead to a better understanding of the nature of the central executive itself.

Distribution and structure of cloned P elements from the Drosophila melanogaster P strain pi 2

P transposable elements of Drosophila melanogaster cloned from the strong P strain pi 2 have been analysed. The structures and chromosomal locations of 26 of the 30-50 elements estimated to be present in pi 2 have been determined. At one location two elements are inserted 100 base pairs (bp) apart, and in a second location two elements are only separated by the 8 bp duplicated upon P-element insertion. In addition to 2.9 kilobase-pair (kbp) elements, elements with 14 different internal deletions from 1.3 to 2.3 kbp in size have been isolated. There are 7 copies of the 2.9 kbp element, 2 copies each of 5 internally deleted elements and a single copy of 9 internally deleted elements. One of the elements found twice is the KP element, which may play a role in the regulation of hybrid dysgenesis in strains which contain many copies of this element. Apart from internal deletions the elements are extremely homogeneous in DNA sequence, with only 2 single base polymorphisms detected twice each in over 16 kbp of P-element sequence. Although transpositions are infrequent in an inbred P cytotype strain such as pi 2, the distribution of these cloned elements indicates that when the genomic library was made, the strain was polymorphic with respect to element location. The distribution and structures of the element are discussed with respect to models for regulation of P-element transposition.

DNA sequence of the Doc retroposon in the white-one mutant of Drosophila melanogaster and of secondary insertions in the phenotypically altered derivatives white-honey and white-eosin

We analysed the structure of the white locus of Drosophila melanogaster in a family of related white mutants. The white-one mutant has bleach white eyes, and a Doc transposable element is inserted into the promotor region of the white locus. The DNA sequence of this Doc insertion was determined, and showed it to be closely related to other Drosophila melanogaster retroposons such as the I factor and the F, G and jockey elements. There are two long open reading frames, which encode a putative nucleic acid binding protein and a putative reverse transcriptase, respectively. Two independent, partially pigmented derivatives were analysed by cloning sequences from this region. In white-honey a transposable element of the retroviral class, B104, is inserted within the Doc element. In white-eosin there is an insertion within the Doc element of a 190 bp sequence that appears to be a member of a novel family of transposable elements. This pogo element is of the same structural class as the Drosophila melanogaster P and hobo elements. These data are consistent with the hypothesis that the Doc retroposon cannot excise, and that, for the white-one mutation, flies with altered phenotypes are most often generated by the insertion of additional transposable elements.

Structural analysis of Doc transposable elements associated with mutations at the white and suppressor of forked loci of Drosophila melanogaster

DNA sequences from two spontaneous mutations of Drosophila melanogaster associated with insertion of a Doc transposable element have been cloned. In white-one, the element is inserted in the white locus close to where transcription initiates. In a lethal allele of suppressor of forked, su(f)S2, the element is inserted within the transcription unit in the protein coding region. Four other Doc elements have been cloned from a wild-type strain. Doc is a member of the class of transposable elements known as retroposons, which includes the D. melanogaster F, G, Jockey, and I elements. There is no sequence homology between the ends of the Doc element. The 3' or right end terminates with a polyadenylation signal sequence followed by a stretch of oligo-A. The length of the oligo-A varies between elements, and a duplication of variable size is found as a direct repeat flanking inserted Doc elements. Members of the family are conserved at the 3' end, but may be truncated at the 5' or left end. These structural features suggest a mechanism of transposition via an RNA intermediate.