Heather A. McQueen

Somatic sex identity is cell autonomous in the chicken.

In the mammalian model of sex determination, embryos are considered to be sexually indifferent until the transient action of a sex-determining gene initiates gonadal differentiation. Although this model is thought to apply to all vertebrates, this has yet to be established. Here we have examined three lateral gynandromorph chickens (a rare, naturally occurring phenomenon in which one side of the animal appears male and the other female) to investigate the sex-determining mechanism in birds. These studies demonstrated that gynandromorph birds are genuine male:female chimaeras, and indicated that male and female avian somatic cells may have an inherent sex identity. To test this hypothesis, we transplanted presumptive mesoderm between embryos of reciprocal sexes to generate embryos containing male:female chimaeric gonads. In contrast to the outcome for mammalian mixed-sex chimaeras, in chicken mixed-sex chimaeras the donor cells were excluded from the functional structures of the host gonad. In an example where female tissue was transplanted into a male host, donor cells contributing to the developing testis retained a female identity and expressed a marker of female function. Our study demonstrates that avian somatic cells possess an inherent sex identity and that, in birds, sexual differentiation is substantively cell autonomous.

Genomic structure and chromosomal mapping of the murine and human Mbd1, Mbd2, Mbd3, and Mbd4 genes

Abstract. DNA methylation is essential for murine development and is implicated in the control of gene expression. MeCP2, MBD1, MBD2, MBD3, and MBD4 comprise a family of mammalian, nuclear proteins related by the presence in each of an amino acid motif called the methyl-CpG binding domain (MBD). Each of these proteins, with the exception of MBD3, is capable of binding specifically to methylated DNA. MeCP2, MBD1 and MBD2 can also repress transcription. We describe the genomic structure and chromosomal localization of the human and murine Mbd1, Mbd2, Mbd3, and Mbd4 genes. We find that the highly similar MBD2 and MBD3 proteins are encoded by genes that map to different chromosomes in humans and mice but show a similar genomic structure. The Mbd1 and Mbd2 genes, in contrast, map together to murine and human Chromosomes (Chrs)18. The Mbd3 and Mbd4 genes map to murine Chrs 10 and 6, respectively, while the human MBD3 and MBD4 genes map to Chrs 19 and 3, respectively.

Chicken Microchromosomes Are Hyperacetylated, Early Replicating, and Gene Rich

The chicken karyotype consists of 39 chromosomes of which 33 are classed as microchromosomes (MICs). MICs contain about one third of genomic DNA. The majority of mapped chicken genes are assigned to macrochromosomes (MACs), but a recent study indicated that CpG islands (CGIs), which are associated with most vertebrate genes, map predominantly to MICs. The present work establishes that chicken genes are concentrated on MICs by several criteria. Acetylated (lysine 5) histone H4, which is strongly correlated with the presence of genes, is highly enriched on MICs by immunocytochemistry. In addition, detailed analysis of chicken cosmids shows that CGI-like fragments are approximately six times denser on MICs than on MACs. Published mapping of randomly chosen genes by fluorescent in situ hybridization (FISH) also shows a significant excess of microchromosomal assignments. Finally, the finding that MICs replicate during the first half of S phase is also compatible with the suggestion that MICs represent gene-rich DNA. We use the cosmid data to predict that approximately 75% of chicken genes are located on microchromosomes. [The sequence data described in this paper have been submitted to the GenBank data library under accession nos. AJ001643 and AJ001644.]

Female-specific hyperacetylation of histone H4 in the chicken Z chromosome

Birds undergo genetic sex determination using a ZW sex chromosome system. Although the avian mechanisms of neither sex determination nor dosage compensation are understood, a female-specific non-coding RNA (MHM) is expressed soon after fertilisation from the single Z chicken chromosome and is likely to have a role in one or both processes. We have now discovered a prominent female-specific modification to the Z chromatin in the region of the MHM locus. We find that chicken chromatin at Zp21, including the MHM locus, is strongly enriched for acetylation of histone H4 at lysine residue 16 in female but not male chromosomes. Interestingly, this specific histone modification is also enriched along the length of the up-regulated Drosophila melanogaster male X chromosome where it plays a vital role in the dosage compensation process.

MBD1, MBD2 and CGBP genes at chromosome 18q21 are infrequently mutated in human colon and lung cancers

The genes MBD1 and MBD2 encode methyl-CpG binding proteins that suppress transcription from methylated promoters. In contrast, CGBP encodes a protein that binds promoters containing unmethylated CpG and stimulates transcription. All three are located on human chromosome 18q21, a region of frequent loss of heterozygosity in several cancers. These genes therefore represent candidate tumour suppressor genes, whose loss of function could affect the normal regulation of gene expression, whether by lack of complete suppression of genes normally silenced (via loss of MBD1 and MBD2) or by some loss of activation of genes normally expressed (via loss of CGBP), either way contributing to the tumorigenic phenotype. We have confirmed by fluorescent in situ hybridization that MBD1 and MBD2 bracket the DCC locus giving a gene order of MBD1/CGBP–DCC 5′-DCC 3′-MBD2. Mutation analyses by single-stranded conformation polymorphism in colon and lung cancer cell lines and primary tumours revealed a small number of mutations, suggesting only a limited role of these genes in human tumorigenesis.

Avian sex chromosomes: dosage compensation matters

In 2001 it was established that, contrary to our previous understanding, a mechanism exists that equalises the expression levels of Z chromosome genes found in male (ZZ) and female (ZW) birds (McQueen et al. 2001). More recent large scale studies have revealed that avian dosage compensation is not a chromosome-wide phenomenon and that the degree of dosage compensation can vary between genes (Itoh et al. 2007; Ellegren et al. 2007). Although, surprisingly, dosage compensation has recently been described as absent in birds (Mank and Ellegren 2009b), this interpretation is not supported by the accumulated evidence, which indicates that a significant proportion of Z chromosome genes show robust dosage compensation and that a particular cluster of such dosage compensated genes can be found on the short arm of the Z chromosome. The implications of this new picture of avian dosage compensation for avian sex determination are discussed, along with a possible mechanism of avian dosage compensation.

Quectures: Personalised constructive learning in lectures:

Active learning exercises engage students during lectures, but often fail to take account of the individual learning position of each student. The ‘quecture’ is a partially flipped lecture that incorporates students posing their own questions (quecture questions), discussing them during lectures and revisiting them later. These interactive learning events are designed to personalise students’ construction of learning during lectures. Quectures were trialled in direct comparison with both fully flipped and traditional lectures, providing information on student attitudes, experiences and engagement with the learning strategy. Quectures were favoured by participants over the two other lecture formats and were found to be helpful both in increasing learning and in improving study habits, although some students had difficulty adjusting to, or disliked, the new mode of learning. The student-posed questions were also perceived by students to improve enquiry skills and to personalise learning. Although many chose not to engage with the strategy, those who did felt more engaged with, and more responsible for their own learning during quectures than in traditional lectures. Future work will be required to generalise the effectiveness of this strategy as well as to fine tune for optimum benefit. It will also be important to investigate which subpopulations of students preferentially engage or disengage with the strategy, and to unpick any relationship between this engagement and academic performance.

15-P020 Cell autonomous sexual development in birds

Our analyses of early neurogenesis in several representatives of chelicerates (e.g. spiders) and myriapods (e.g. millipedes) have revealed that the genetic network involved in recruitment and specification of neural precursors is conserved in all euarthropod groups. However, the expression pattern and function of these genes is adapted to the distinct morphology of neural precursor formation in each group. We observed several molecular and morphological characters in the developing central and peripheral nervous system of chelicerates and myriapods that cannot be found in equivalent form in insects and crustaceans. It is possible that these characters are shared derived characters (synapomorphies) of myriapods and chelicerates, providing the first morphological support for a clade uniting these two groups. However, they could also represent ancestral characters (symplesiomorphies) retained in myriapods and chelicerates and lost in the more derived insects and crustaceans. We have therefore analysed neurogenesis in a representative of an outgroup to the euarthropods, the onychophoran Euperipatoides kanangrensis. We have identified Notch and Delta homologues in Euperipatoides kanangrensis. These genes are involved in specification of neural stem cells in insects. We show that they are expressed in a distinct pattern which is neither comparable to insects/crustaceans nor to chelicerates/myriapods. Furthermore, we have analysed the morphology of neural precursor formation by F-actin staining and light microscopic sections. The data suggest that at least some of the characters shared by chelicerates and myriapods are synapomorphies