The grasshopper X chromosome. I. States of condensation and the nuclear envelope at G1, S and G2 of premeiotic interphase and at early meiotic prophase.
The sub-stages of spermatocyte interphase (G1, S and G2) have been identified in the grasshopper Brachystola magna using E.M. autoradiography and serial thin sectioning techniques. The X chromosome occupies a nuclear envelope bound compartment separate from an autosome compartment during G1 and S. At G2 the X compartment is resolved by coalescence of the membranes enveloping the X chromosome and autosome compartments.--At G1 and S, the compartmentalized X chromatin is laced with nuclear membrane material. This X chromatin associated membrane decreases in amount as the cell passes through G2 and enters early meiotic prophase. There are at least 2 and possibly 3 states of condensation of the heterochromatic X during premeiotic interphase and early meiotic prophase correlated with the presence or absence of membrane material associated with the chromatin.--The X chromatin replicates asynchronously with autosomal euchromatin and synchronously with autosomal heterochromatin associated with nucleoli. The X chromatin replication appears to be associated with the nuclear membrane.--The observations indicate that the nuclear membrane is involved with X chromosome condensation and may be implicated in asynchronous X chromosome replication as well.
D000818:Animals; D002453:Cell Cycle; D002467:Cell Nucleus / Q000648:ultrastructure; D005260:Female; D006110:Grasshoppers / Q000235:genetics*; D007399:Interphase; D007425:Intracellular Membranes / Q000648:ultrastructure; D008297:Male; D008540:Meiosis; D008854:Microscopy, Electron; D012730:Sex Chromosomes / Q000648:ultrastructure*; D014960:X Chromosome / Q000648:ultrastructure*