Which phase show a notch in the cytoplasm in between the center region
Answers
The microtrabecular lattice may influence differentiation of cell types. Cell differentiation may be brought about by the differential localization of various determinants in embryos (Wilson, 1925; Davison, 1976). These cytoplasmic determinants appear to be, in part, maternal messenger RNA molecules. The cytoplasmic determinants are localized in various regions of the egg cell, and are selectively distributed to particular embryonic cell lineages where they may initiate specific developmental programs (Jeffrey, 1982, 1984a,b, 1985Jeffrey 1982Jeffrey 1984aJeffrey 1984bJeffrey 1985; Jeffrey and Wilson, 1983; Jeffrey et al., 1983; Jeffrey and Meier, 1984; Swalla et al., 1985). The eggs have three distinct regions with specific morphogenetic fates: the ectoplasm, endoplasm, and myoplasm. I will only discuss the myoplasm, which gives rise to muscle cells. When radiolabeled poly-U is used as an in situ hybridization probe for poly-A RNA, a general feature of all messenger RNAs (see Chapter 16), it is found that 45 percent of the poly-A RNA is in the ectoplasm, 50 percent is in the endoplasm, and 5 percent is in the myoplasm. However, when a radiolabeled actin cDNA is used, it is found that 40 percent of the actin mRNA is present in the ectoplasm, 15 percent is in the endoplasm, and 45 percent is in the myoplasm. Thus, the myoplasm, which is destined to be muscle, is specifically enriched in actin mRNA.
When the eggs are extensively extracted with Triton X-100 so that almost everything in the cell is washed away, a detergent-resistant lattice remains. This lattice includes actin, tubulin, and intermediate filaments. When this lattice is probed with radiolabeled cDNA using in situ hybridization, it is found that the actin mRNA is bound to the lattice and remains in the same position it was in before detergent extraction. It appears that the cytoplasmic lattice can help maintain a polarity in cells so that the daughter cells of a division get unequal components, which may determine their developmental fate.
Cytokinesis .
In plants cell , cell plate formation takes place then cytokinesis takes place.