Yancey S B, Koh K, Chung J, Revel J P
Division of Biology, California Institute of Technology, Pasadena 91125.
J Cell Biol. 1988 Mar;106(3):705-14. doi: 10.1083/jcb.106.3.705.
The main intrinsic polypeptide (MIP) is the major protein present in the lens fiber cell membrane and is the product of a gene which, as far as is known, is expressed only in the lens. We have used in situ hybridization and immunofluorescence microscopy to characterize the expression of this gene during the course of development in the rat. At progressive stages of lens morphogenesis, we find that synthesis of the protein is closely tied to the accumulation of MIP mRNA in cells that are committed to terminal differentiation, first in the elongating presumptive primary lens fibers and later in the secondary fibers as they differentiate from the anterior epithelial cells. The transcripts accumulate in the basal cytoplasm of the primary fibers and in the cytoplasm which surrounds the cell nucleus in the secondary fibers. We have compared this pattern of expression with that of a gene for a cytoplasmic protein, beta-crystallin beta-A1/A3. In sharp contrast to the localized concentrations seen for the MIP mRNA, beta-A1/A3 transcripts are relatively uniformly distributed throughout the cytoplasm. Neither MIP nor crystallin gene appears to be transcriptionally active in the undifferentiated epithelial cell, but transcripts from the beta-A1/A3 gene appear earlier in fiber cell differentiation than do those from the gene for MIP.
主要内在多肽（MIP）是晶状体纤维细胞膜中存在的主要蛋白质，是一个基因的产物，据目前所知，该基因仅在晶状体中表达。我们利用原位杂交和免疫荧光显微镜技术来表征该基因在大鼠发育过程中的表达情况。在晶状体形态发生的不同阶段，我们发现蛋白质的合成与MIP mRNA在致力于终末分化的细胞中的积累密切相关，首先是在伸长的初级晶状体纤维前体细胞中，随后是在从前部上皮细胞分化而来的次级纤维中。转录本在初级纤维的基底细胞质以及次级纤维中围绕细胞核的细胞质中积累。我们将这种表达模式与一种细胞质蛋白β-晶体蛋白β-A1/A3的基因的表达模式进行了比较。与MIP mRNA的局部浓度形成鲜明对比的是，β-A1/A3转录本相对均匀地分布在整个细胞质中。MIP基因和晶体蛋白基因在未分化的上皮细胞中似乎都没有转录活性，但β-A1/A3基因的转录本在纤维细胞分化中比MIP基因的转录本出现得更早。
