Riemer D, Stuurman N, Berrios M, Hunter C, Fisher P A, Weber K
Max-Planck-Institute for Biophysical Chemistry, Department of Biochemistry, Goettingen, FRG.
J Cell Sci. 1995 Oct;108 ( Pt 10):3189-98. doi: 10.1242/jcs.108.10.3189.
Vertebrate nuclear lamins form a multigene family with developmentally controlled expression. In contrast, invertebrates have long been thought to contain only a single lamin, which in Drosophila is the well-characterized lamin Dm0. Recently, however, a Drosophila cDNA clone (pG-IF) has been identified that codes for an intermediate filament protein which harbors a nuclear localization signal but lacks a carboxy-terminal CAAX motif. Based on these data the putative protein encoded by pG-IF was tentatively called Drosophila lamin C. To address whether the pG-IF encoded protein is expressed and whether it encodes a cytoplasmic intermediate filament protein or a nuclear lamin we raised antibodies against the recombinant pG-IF protein. The antibodies decorate the nuclear envelope in Drosophila Kc tissue culture cells as well as in salivary and accessory glands demonstrating that pG-IF encodes a nuclear lamin (lamin C). Antibody decoration, in situ hybridization, western and northern blotting studies show that lamin C is acquired late in embryogenesis. In contrast, lamin Dm0 is constitutively expressed. Lamin C is first detected in late stage 12 embryos in oenocytes, hindgut and posterior spiracles and subsequently also in other differentiated tissues. In third instar larvae lamins C and Dm0 are coexpressed in all tissues tested. Thus, Drosophila has two lamins: lamin Dm0, containing a CaaX motif, is expressed throughout, while lamin C, lacking a CaaX motif, is expressed only later in development. Expression of Drosophila lamin C is similar to that of vertebrate lamin A (plus C), which loses its CaaX motif during incorporation into the lamina.
脊椎动物的核纤层蛋白形成一个受发育调控表达的多基因家族。相比之下，长期以来人们一直认为无脊椎动物只含有一种核纤层蛋白，在果蝇中这种核纤层蛋白就是特征明确的核纤层蛋白Dm0。然而，最近已鉴定出一个果蝇cDNA克隆（pG-IF），它编码一种中间丝蛋白，该蛋白带有核定位信号但缺乏羧基末端CAAX基序。基于这些数据，由pG-IF编码的假定蛋白被暂定为果蝇核纤层蛋白C。为了确定pG-IF编码的蛋白是否表达，以及它编码的是细胞质中间丝蛋白还是核纤层蛋白，我们制备了针对重组pG-IF蛋白的抗体。这些抗体在果蝇Kc组织培养细胞以及唾液腺和附属腺中标记核膜，表明pG-IF编码一种核纤层蛋白（核纤层蛋白C）。抗体标记、原位杂交、蛋白质免疫印迹和Northern印迹研究表明核纤层蛋白C在胚胎发育后期获得。相比之下，核纤层蛋白Dm0是组成性表达的。核纤层蛋白C首先在12期晚期胚胎的oenocytes、后肠和后气门中检测到，随后也在其他分化组织中检测到。在三龄幼虫中，核纤层蛋白C和Dm0在所有测试组织中共同表达。因此，果蝇有两种核纤层蛋白：含有CaaX基序的核纤层蛋白Dm0在整个发育过程中都有表达，而缺乏CaaX基序的核纤层蛋白C只在发育后期表达。果蝇核纤层蛋白C的表达与脊椎动物核纤层蛋白A（加C）相似，后者在整合到核纤层的过程中失去其CaaX基序。
