robert remak discovered that cells originate from division of existing cells.
who discovered that cells originate from division of existing cells?
robert remak
virchow is credited with several very important discoveries. his most widely known scientific contribution is his cell theory, which built on the work of theodor schwann. he was one of the first to accept the work of robert remak, who showed the origins of cells was the division of pre-existing cells. he did not initially accept the evidence for cell division, believing that it occurs only in certain types of cells. when it dawned on him that remak might be right, in 1855, he published remak's work as his own, causing a falling-out between the two. virchow was particularly influenced in cellular theory by the work of john goodsir of edinburgh, whom he described, as "one of the earliest and most acute observers of cell-life both physiological and pathological." virchow dedicated his "magnum opus" "die cellularpathologie" to goodsir. virchow's cellular theory was encapsulated in the epigram "omnis cellula e cellula" ("all cells (come) from cells"), which he published in 1855. (the epigram was actually coined by françois-vincent raspail, but popularized by virchow.) it is a rejection of the concept of spontaneous generation, which held that organisms could arise from nonliving matter. for example, maggots were believed to appear spontaneously in decaying meat; francesco redi carried out experiments which disproved this notion and coined the maxim "omne vivum ex ovo" ("every living thing comes from a living thing" — literally "from an egg"); virchow (and his predecessors) extended this to state that the only source for a living cell was another living cell.
rudolf virchow
in human fetal pancreases, single ε-cells scatter in primitive exocrine tissue and are observed to start aggregating into clusters after gestational week 13. peak ghrelin levels are observed at week 14 of gestation. from gestational week 21, ε-cells are observed around developing islets in humans, forming an almost continuous layer at the rim of the islets. ε-cells are found centralized in the mouse fetal pancreas, with a few also observed in the stomach. these results in mice pancreas were discovered and confirmed with the use of confocal microscopy, which is able to collect images of thick specimens and exclude fluorescent areas outside of the focal plane. these islet cells are the main source of ghrelin during development. ghrelin released from ε-cells have been found to promote cell growth and proliferation while also inhibiting apoptosis of pancreatic beta cells in the human pancreas. some ε-cells express cytokeratin 20, a marker of duct cells and islet precursor cells, hinting that these islet cells originate from the ductal epithelium. the development of these cells derive from the "ngn3" transcription factor. mice with mutant nkx2.2 genes show an increase of ε-cells. on a cellular level, ε-cells co-produce both nkx2-2 and isl1, but not nks6-1 and pax6 as was previously hypothesized. furthermore, this type of cell co-produces isl1 which plays a role in the development of the mesenchyme of the dorsal pancreatic bud, and the differentiation of the dorsal pancreatic epithelium into endocrine cells. a total of 36 genes are significantly enriched in ε-cells that aid in proteinase inhibition, processing of hormones, cell migration, and immune activity that differentiates them from α-, β-, δ- and pp-cells. additionally, the secretory vesicles of ε-cells (110±3 nm) are much smaller than those of α-cells (185±7 nm). unlike the other pancreatic islet cells, ε-cells also do not produce other pancreatic hormones (insulin, glucagon, homeostatic) and they do not express the cart peptide. examples of specific genes that influence ε-cells are acyl-coenzyme a synthetase long chain family member 1 (acsl1) and defensin beta 1. acsl1 is thought to play a role in the processing of ghrelin while defensin beta 1 produces a protein that can kill bacteria, viruses, and yeast to regulate immunity. after birth, the number of ε-cells decrease and become rare into adulthood. studies in mice, desert gerbil, and african ice rats have all yielded closely related results on this topic.
epsilon cell