FUNCTION OF N-MYC PROTEIN IN LYMPHOCYTE DIFFERENTIATION

N-myc是原癌基因家族中的一员，它编码相关的 不同的核蛋白。MYC基因是可能的转录因子 它们被认为在基因表达的调节中起作用 细胞生长和分化的背景。然而，确切的函数 Myc基因的具体情况尚不清楚。每个myc基因都与一个唯一的 自发性肿瘤的组织特异性模式，部分地 反映正常发育过程中的表达模式。这一发现 小鼠种系纯合子时N-myc的零突变是 胚胎致死提示N-myc发挥着独特的生理作用 在开发过程中。 N-myc在B淋巴细胞发育过程中受到高度调控。前B细胞 同时表达c-myc和N-myc。C-myc和N-myc mRNA的表达为 前B细胞特异性处理对正常前B细胞的诱导 生长因子IL-7；在这个阶段，调节是通过释放一种 阻断转录延伸。当细胞成熟为B细胞时 阶段，N-myc转录启动下调，而c-myc转录启动下调 继续被表达出来。综上所述，这些发现表明N-myc 在B细胞发育的早期阶段有特定的功能。我们 假设前体B细胞的扩增需要N-myc 或者通过促进他们的成长，抑制他们的死亡，和/或 阻止它们的终末分化。这些研究的目标是 准确定位N-myc在B淋巴细胞发育中的作用 以及它与c-myc功能的关系。N-myc如何参与 其他造血谱系的确定也将被检查。 B淋巴细胞和T淋巴细胞分化的确切阶段 将确定N-myc何时表达。此表达式将为 与其中其他阶段特定特征的表达相关 血统。N-myc零突变对先天性巨结肠发育的影响 而未受精的祖细胞将被确定。如果一个成熟的 B细胞发育受阻，处于分化阶段 它的发生将被定义和描述。转型和 未转化的细胞系将被派生出来以确定如何 其他阶段特异性基因的表达受N-myc缺失的影响 表情。这些细胞对生长因子和有丝分裂的反应 信号将被测试。提出了一种新的推导方法。 代表B细胞分化阶段的永生化细胞系 并保留了充分的差异化能力。使用“Hit” 和Run“基因打靶技术，每个myc内的序列 决定其在淋巴细胞内的独特功能的基因 差异化将被确定。最后，我们将确定N-myc是否 可能通过诱导细胞凋亡或调节在造血过程中发挥作用 C-myc诱导的细胞凋亡。 除了提供对潜在的分子机制的洞察 淋巴细胞发育，这些研究也可能产生关于 MYC基因在胚胎发育过程中的一般功能及其转录 各种因素在发育过程中发挥作用。此外，一个 了解myc基因如何在正常发育中发挥作用可能会揭示 不恰当的表达如何导致肿瘤发生。

N-myc is a member of a family of proto-oncogenes that encode related but distinct nuclear proteins. Myc genes are putative transcription factors that are thought to function in the regulation of gene expression in the context of cell growth and differentiation. However, the exact function of myc genes is unknown. Each myc gene is associated with a unique tissue-specific pattern of spontaneously arising tumors that partially reflects the expression pattern in normal development. The finding that a null mutation of N-myc when homozygous in the germline of the mouse is embryonic lethal suggests that N-myc plays a unique physiological role during development. N-myc is highly regulated during B lymphocyte development. Pre-B cells express both c-myc and N-myc. The expression of c-myc and N-myc mRNA is induced in normal pre-B cells by treatment with the pre-B cell specific growth factor IL-7; at this stage, regulation is mediated by releasing a block to transcriptional elongation. When cells mature to the B cell stage, transcriptional initiation of N-myc is down-regulated, while c-myc continues to be expressed. Together, these findings suggest that N-myc has a specific function in the early stages of B cell development. We hypothesize that N-myc is required for the expansion of precursor B cells either by promoting their growth, inhibiting their death, and/or preventing their terminal differentiation. The goal of these studies is to define precisely the function of N-myc during B lymphocyte development and how it relates to c-myc function. How N-myc may be involved in determination of other hematopoietic lineages will also be examined. The exact stages within B lymphocyte and T lymphocyte differentiation when N-myc is expressed will be determined. This expression will be correlated with expression of other stage-specific features within that lineage. The affect of a null N-myc mutation on development of committed and uncommitted progenitor cells will be determined. If a maturational block in B cell development is found, the differentiation stage at which it occurs will be defined and characterized. Transformed and nontransformed cell lines will be derived in order to determine how expression of other stage-specific genes are affected by lack of N-myc expression. The response of these cells to growth factor and mitogenic signals will be tested. A novel approach is presented for the derivation of immortalized cell lines that represent B cell differentiation stages and that retain full differentiative capacity is presented. Using "hit and run" gene targeting techniques, the sequences within each of the myc genes that determine their unique functions within lymphocyte differentiation will be determined. Finally, we will determine if N-myc may function during hematopoiesis by induction of apoptosis or modulation of c-myc-induced apoptosis. Besides providing insights into the molecular mechanisms underlying lymphocyte development, these studies may also yield revelations about myc gene function generally during embryogenesis and how transcription factors function in developmental processes. Furthermore, an understanding of how myc genes function in normal development may reveal how inappropriate expression leads to oncogenesis.