Mechanisms Of Lineage-specific Gene Expression

本项目重点研究最初在B淋巴细胞中发现的转录因子HB9和BSAP。HB9基因也被称为HlxB9，编码一种同源结构域编码蛋白。小鼠的基因靶向研究揭示了HB9在运动神经元和胰腺发育中的关键作用。有一个HB9等位基因异常的人在骶骨区域会出现异常。HB9零突变的杂合子小鼠是正常的，但缺乏HB9的小鼠在出生时死于呼吸衰竭，这是由于缺乏膈神经支配。运动神经元缺陷可能是由于在其他类型的神经元中正常表达的基因表达不当而引起的。这些小鼠也缺少了一部分胰腺，即胰腺的背叶，并且在剩余的腹叶中产生胰岛素的β细胞数量减少。由于发育缺陷和围产期致死率使得无法评估HB9在成人组织中的功能，我们使用了条件基因靶向方法，并在HB9基因3外显子的两侧引入了loxP位点。我们已经证明，引入LoxP位点不会干扰正常的HB9表达。我们已经获得了MX-Cre转基因小鼠，其中Cre重组酶可以通过干扰素治疗诱导。我们将MX-Cre转基因引入HB9 loxP背景。我们发现Cre的表达导致HB9外显子3的缺失，但良好的缺失只发生在脾脏、骨髓和肠道中。相比之下，我们在胰腺中发现很少缺失。我们发现在那些表达Cre的组织中删除HB9几乎没有效果。为了确定在发育和成年胰腺中删除HB9的后果，我们将HB9 Cre突变小鼠与表达由胰岛素启动子调控的转基因Cre的小鼠杂交。在HB9外显子3两侧的两个等位基因上都有loxP位点，并且表达来自胰岛素启动子的Cre的小鼠应该可以在今年秋天进行分析。BSAP是对b淋巴细胞发育和谱系承诺至关重要的转录因子。过表达BSAP的小鼠B细胞增殖过度，有细胞凋亡缺陷，并有发生淋巴瘤的倾向。我们已经基本完成了对这些老鼠的分析。

This project focuses on the transcription factors HB9 and BSAP, originally identified in B lymphocytes. The HB9 gene also referred to as HlxB9 encodes a homeodomain coding protein. Gene targeting in mice has revealed a critical role for HB9 in motor neuron and pancreas development. Abnormalities in the sacral region occurs in humans with one abnormal HB9 allele. Mice heterozygotic for an HB9 null mutation are normal, but mice that lack HB9 die at birth of respiratory failure due to a lack of diaphragm innervation. The motor neuron defects may arise from the inappropriate expression of genes normally expressed in other types of neurons. These mice also lack a portion of their pancreas, the dorsal lobe, and have reduced numbers of insulin producing beta cells in their residual ventral lobe. Because the developmental defects and perinatal lethality makes assesmment of the function of HB9 in adult tissues impossible, we have used a conditional gene targeting approach and have introduced loxP sites on either side of exon 3 of the HB9 gene. We have shown that the introduction of the LoxP sites does not interfere with normal HB9 expression. We have obtained MX-Cre transgenic mice, where the Cre recombinase can be induced by interferon treatment. We have introduced the MX-Cre transgene onto the HB9 loxP background. We have shown that the expression of Cre causes the deletion of exon 3 of HB9, but good deletion only occured in spleen, bone marrow, and intestine. In contrast, we found little deletion in the pancreas. We have found little effect on deleting HB9 in those tissues where Cre is expressed. To determine the consequences of deleting HB9 in the developing and adult pancrease we have crossed the HB9 Cre lox mice with mice expressing Cre from a transgene regulated by the insulin promoter. Mice in which HB9 exon 3 is flanked by loxP sites on both alleles and which express Cre from the insulin promoter should be available this fall for analysis. BSAP is a transcription factor critical for B-lymphocyte development and lineage committment. Mice overexpressing BSAP have B cells which are hyperproliferative, have an apoptosis defect, and a propensity for developing lymphomas. We have largely completed the analysis of these mice.