金鱼Prox1基因cDNA的克隆及其在眼睛发育中的表达分析

脊椎动物的Prox1基因,与果蝇的转录因子prospero同源。为了探讨Prox1基因在金鱼眼睛发生过程中的表达图式,我们从金鱼眼睛SMART库中克隆了Prox1cDNA。它全长共2851bp,编码739个氨基酸。组织分布研究表明,Prox1主要分布于眼、脑、心、肝、脾和肾中。整体原位杂交显示,Prox1mRNA首先是在晶体期的晶体原基中有转录,心跳期则在未成熟晶体的细胞中和视网膜的幼芽区可以检测到。晶体纤维形成后,它主要定位于视纤维层和内网织细胞层。免疫组化显示,心跳期Prox1蛋白的定位与mRNA相同,晶体纤维形成以后,Prox1蛋白主要定位在晶体上皮细胞内侧的晶体纤维上一个环状区域,与Prox1mRNA的定位不同。这说明,Prox1基因在晶体发生过程中有重要作用,且在晶体的不同发育时期起的作用可能有所不同。另外,Prox1在晶体发育过程中有一个从内向外的变化过程。     

Prox 1 in eye degeneration and sensory organ compensation during development and evolution of the cavefish Astyanax

We have investigated expression of the homeobox gene Prox 1 during eye degeneration and sensory organ compensation in cavefish embryos. The teleost Astyanax mexicanus consists of sighted surface-dwelling forms (surface fish) and several populations of blind cave-dwelling forms (cavefish), which have evolved independently. Eye formation is initiated during cavefish development, but the lens vesicle undergoes apoptosis, and the eye subsequently arrests and degenerates. The requirement of Prox 1 for lens fiber differentiation and γ-crystallin expression in the mouse suggests that changes in the expression of this gene could be involved in cavefish eye degeneration. Surface fish and cavefish embryos stained with a Prox 1 antibody showed Prox 1 expression in the lens, neuroretina, myotomes, heart, hindbrain, and gut, as reported in other vertebrates. We found that Prox 1 expression is not altered during cavefish lens development. Prox 1 protein was detected in the lens vesicle as soon as it formed and persisted until the time of lens degeneration in each cavefish population. The cavefish lens vesicle was also shown to express a γ-crystallin gene, suggesting that Prox 1 is functional in cavefish lens development. In addition to the tissues described above, Prox 1 is expressed in developing taste buds and neuromasts in cavefish, which are enhanced to compensate for blindness. It is concluded that the Prox 1 gene is not involved in lens degeneration, but that expansion of the Prox 1 expression domain occurs during taste bud and neuromast development in cavefish. Received: 31 July 1999 / Accepted: 8 November 1999     

Coupling Glial Numbers and Axonal Patterns

The control of the rate of cell division enables cells to respond to signals from other cells and this promotes the emergence of order as cell mass increases during growth. Glial cell proliferation is coupled to axon guidance, and the sequential deployment of glial cells in constrained numbers enables the sequential sorting out of axons into appropriate trajectories through time1. This is achieved by the neuron-dependent regulation of glial division at the G1 phase. Early on, Prospero plays a key role controlling the G1 phase and it enables the glia to proliferate in response to neurons. Later, Prospero maintains subsets of glia in G1 arrest, retaining mitotic potential, whereas non-Prospero glia terminally differentiate. Only this population of Prospero quiescent precursors can overproliferate when neurons are eliminated, inducing a repair response. It is compelling to investigate whether the vertebrate homologue Prox1 may enable the repair response of vertebrate glia.     

Structure and Chromosomal Localization of the Human Homeobox Gene Prox 1

The genomic organization and nucleotide sequence of the human homeobox gene Prox 1 as well as its chromosomal localization have been determined. This gene spans more than 40 kb, consists of at least 5 exons, and encodes an 83-kDa protein. It shows 89% identity with the chicken sequence at the nucleotide level in the coding region, while the human and chicken proteins are 94% identical. Among the embryonic tissues analyzed (lens, brain, lung, liver, and kidney), the human Prox 1 gene is most actively expressed in the developing lens, similar to the expression pattern of the chicken Prox 1 gene. The Prox 1 gene was mapped to human chromosome 1q32.2–q32.3.     

Fibroblast growth factor receptor signaling is essential for lens fiber cell differentiation

The vertebrate lens provides an excellent model to study the mechanisms that regulate terminal differentiation. Although fibroblast growth factors (FGFs) are thought to be important for lens cell differentiation, it is unclear which FGF receptors mediate these processes during different stages of lens development. Deletion of three FGF receptors (Fgfr1-3) early in lens development demonstrated that expression of only a single allele of Fgfr2 or Fgfr3 was sufficient for grossly normal lens development, while mice possessing only a single Fgfr1 allele developed cataracts and microphthalmia. Profound defects were observed in lenses lacking all three Fgfrs. These included lack of fiber cell elongation, abnormal proliferation in prospective lens fiber cells, reduced expression of the cell cycle inhibitors p27^kip1 and p57^kip2, increased apoptosis and aberrant or reduced expression of Prox1, Pax6, c-Maf, E-cadherin and α-, β- and γ-crystallins. Therefore, while signaling by FGF receptors is essential for lens fiber differentiation, different FGF receptors function redundantly.     

Drosophila GTPase nucleostemin 2 changes cellular distribution during larval development and the GTP-binding motif is essential to nucleoplasmic localization

Nucleostemin (NS), a nucleolar guanosine triphosphate (GTP)-binding protein, plays significant roles in cell cycle progression and ribosomal biogenesis. Drosophila Nucleostemin 2 (NS2), a member of the Drosophila NS family, regulates early eye development and is essential to cell survival in vivo, but the underlying mechanisms have yet to be clarified. Biochemical analysis using the recombinant NS2 protein indicated that NS2 has GTPase activity. Immunohistochemistry revealed that NS2 changes in subcellular locus from the nucleolus to the nucleoplasm during larval development, and that a mutation in the ATP/GTP-binding site motif A (p-loop) prevents nuclear localization of NS2 and results in cytoplasmic distribution. Furthermore, downregulation of NS2 altered the rRNA proportions between the nucleus and the cytoplasm. These results suggest that NS2 at least requires GTP to import into the nucleoplasm.