You will see from my first post below that there is only a 1-2% difference in DNA sequence between human and chimpanzee. This post will perhaps only be meaningful to experts. These are research papers that describe specific genes that are expressed in the midbrain during development. The title to the paper appears in bold type. The next step for me is to go to the gene databases and to find the DNA sequence differences (if any) between these genes in the human and chimpanzee.

1. Differential Display of Genes Expressed at the Midbrain – Hindbrain Junction Identifies sprouty2: An FGF8-Inducible Member of a Family of Intracellular FGF Antagonists - A clone upregulated in cDNA derived from rhombomere 1 tissue showed a 91% identity at the nucleotide level to the putative human receptor tyrosine kinase antagonist: sprouty2. In situ hybridization on whole chick embryos showed chick sprouty2 to be expressed initially within the isthmus and rhombomere 1, spatially and temporally coincident with Fgf8 expression. However, at later stages this domain was more extensive than that of Fgf8. Introduction of ligand-coated beads into either midbrain or hindbrain region revealed that sprouty2 could be rapidly induced by FGF8. These data suggest that sprouty2 participates in a negative feedback regulatory loop to modulate the patterning activity of FGF8 at the isthmus

2. Cyclopia and defective axial patterning in mice lacking Sonic hedgehog gene function - Targeted gene disruption in the mouse shows that the Sonic hedgehog(Shh) gene plays a critical role in patterning of vertebrate embryonic tissues, including the brain and spinal cord, the axial skeleton and the limbs.

3. Pax-5 is expressed at the midbrain-hindbrain boundary during mouse development - Pax-5 was expressed in the developing brain, predominantly at the midbrain-hindbrain boundary, and in the neural tube. While the neural tube expression pattern overlapped completely with Pax-2 and Pax-8, the expression pattern in the brain was only partially overlapping. Unlike Pax-2 and Pax-8, Pax-5 was not expressed in the developing excretory system, thyroid, eye or ear. Our data suggest that Pax-5 has a role in the development of the central nervous system.

4. The midbrain-hindbrain phenotype of Wnt-1 (minus) mice results from stepwise deletion of engrailed-expressing cells by 9.5 days postcoitum - By examining embryonic expression of the mouse engrailed (En) genes, from 8.0 to 9.5 days postcoitum, we demonstrate that Wnt-1 primarily regulates midbrain development. The midbrain itself is required for normal development of the metencephalon. Wnt-1 and a related gene, Wnt-3a, are coexpressed from early somite stages in dorsal aspects of the myelencephalon and spinal cord. We suggest that functional redundancy between these two genes accounts for the lack of a caudal central nervous system phenotype.

5. Foxa1 and Foxa2 regulate multiple phases of midbrain dopaminergic neuron development in a dosage-dependent manner - The role of transcription factors in regulating the development of midbrain dopaminergic (mDA) neurons is intensively studied owing to the involvement of these neurons in diverse neurological disorders. Here we demonstrate novel roles for the forkhead/winged helix transcription factors Foxa1 and Foxa2 in the specification and differentiation of mDA neurons by analysing the phenotype of Foxa1 and Foxa2 single- and double-mutant mouse embryos. During specification, Foxa1 and Foxa2 regulate the extent of neurogenesis in mDA progenitors by positively regulating Ngn2 (Neurog2) expression. Subsequently, Foxa1 and Foxa2 regulate the expression of Nurr1 (Nr4a2) and engrailed 1 in immature neurons and the expression of aromatic l-amino acid decarboxylase and tyrosine hydroxylase in mature neurons during early and late differentiation of midbrain dopaminergic neurons. Interestingly, genetic evidence indicates that these functions require different gene dosages of Foxa1 and Foxa2.

6. A MicroRNA Feedback Circuit in Midbrain Dopamine Neurons - MicroRNAs (miRNAs) are evolutionarily conserved, 18- to 25-nucleotide, non–protein coding transcripts that posttranscriptionally regulate gene expression during development. miRNAs also occur in postmitotic cells, such as neurons in the mammalian central nervous system, but their function is less well characterized. We investigated the role of miRNAs in mammalian midbrain dopaminergic neurons (DNs). We identified a miRNA, miR-133b, that is specifically expressed in midbrain DNs.

7. Expression patterns of the homeo box-containing genes En-1 and En-2 and the proto-oncogene int-1 diverge during mouse development - We have compared the expression of the murine genes En-1,En-2, and in-1 during development by in situ hybridization. Expression of all three genes was first detected at 8.0 days in overlapping bands of the anterior neural folds. By 12.0 days the expression patterns diverged. En-1 and En-2 were expressed in a similar ring of cells in the central nervous system (CNS) at the midbrain/hindbrain junction.

8. Mutations in zebrafish genes affecting the formation of the boundary between midbrain and hindbrain - Mutations in two genes affect the formation of the boundary between midbrain and hindbrain (MHB): no isthmus (noi) and acerebellar (ace). noi mutant embryos lack the MHB constriction, the cerebellum and optic tectum, as well as the pronephric duct. Analysis of noi mutant embryos with neuron-specific antibodies shows that the MHB region and the dorsal and ventral midbrain are absent or abnormal, but that the rostral hindbrain is unaffected with the exception of the cerebellum. Using markers that are expressed during its formation (eng, wnt1 and pax-b), we find that the MHB region is already misspecified in noi mutant embryos during late gastrulation.

9. The caudal limit of Otx2 gene expression as a marker of the midbrain/hindbrain boundary: a study using in situ hybridisation and chick/quail homotopic grafts - Chick/quail homotopic grafts of various portions of the midbrain/hindbrain domain have shown that the progeny of the cells located in the caudal mesencephalic vesicle at stage HH10 are found within the rhombomere 1 as early as stage HH14. Furthermore, our results indicate that the cells forming the HH20 constriction (coinciding with the caudal Otx2 limit) are the progeny of those located at the caudal Otx2 limit at stage HH10 (within the mesencephalic vesicle). As a result, the Otx2-positive portion of the HH10 mesencephalic vesicle gives rise to the HH20 mesencephalon, while the Otx2-negative portion gives rise to the HH20 rostral rhombomere 1.

10. Inactivation of the (β)-catenin gene by Wnt1-Cre-mediated deletion results in dramatic brain malformation and failure of craniofacial development - ('bgr;)-Catenin is a central component of both the cadherin-catenin cell adhesion complex and the Wnt signaling pathway. We have investigated the role of (β)-catenin during brain morphogenesis, by specifically inactivating the (β)-catenin gene in the region of Wnt1 expression. To achieve this, mice with a conditional ('floxed') allele of (β)-catenin with required exons flanked by loxP recombination sequences were intercrossed with transgenic mice that expressed Cre recombinase under control of Wnt1 regulatory sequences. (β)-catenin gene deletion resulted in dramatic brain malformation and failure of craniofacial development. Absence of part of the midbrain and all of the cerebellum is reminiscent of the conventional Wnt1 knockout (Wnt1(−)(/)(−)), suggesting that Wnt1 acts through (β)-catenin in controlling midbrain-hindbrain development.

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