chiaravi@silver.bacs.indiana.edu (Lucius Chiaraviglio) (03/13/89)
_ This is actually in response to several of the recent sci.space articles about embryonic development in zero gravity. In article <466@jarthur.Claremont.EDU> jokim@jarthur.UUCP (John H. Kim) writes: >I vaguely recall (sorry, don't remember where) a study that found out >that fetal development in bird eggs involved the cells at the bottom of >the undifferentiated cell mass *always* differentiated into the head (or >some other specific body part--I don't remember). The obvious >conclusion would be that gravity provides a sort of compass for the same >types of cells (neural, muscular, etc) to aggregate in the same place. >I think the source went on to say something about babies conceived and >developed without gravity possibly ending up as just a mass of cells. The problem with generalizing observations of birds, reptiles, and amphibians to all vertebrates is that these vertebrates (and at least most if not all fish) have very large yolky eggs whose cell division is distorted by the yolk, which is itself influenced by gravity (it is heavier, so non-yolky parts of the egg float over it. Thus it makes sense that embryonic development in these animals might evolve to take cues from gravity. Effects of gravity on Xenopus development have already been demonstrated, but of course the effect of zero gravity has not been tested. Thus, even this is not necessarily an example of Xenopus (or its ancestors) having evolved specifically to take a cue from gravity, but may just be an example of development proceeding abnormally as a result of gravity in the wrong direction. Reason for suspecting the latter comes from the same experiments showing the effects of gravity in the wrong direction, in which some of the eggs are immune to these effects -- the immunity has been shown to be directly correlated with rigidity of the cytoplasm of the eggs, which tends to prevent the cytoplasm from being sheared out of alignment with the cortex (which is what usually happens to eggs held at the wrong orientation). I got this information in personal communication with the principal investigators performing these experiments and discovering the effect of cytoplasmic rigidity: Tony Neff and George Malacinski at Indiana University. (This information is also published, but I can't remember which journal it was published in.) Even if the above-mentioned vertebrates do take actual developmental cues from gravity, it is unlikely that mammals do so. First of all, mammalian eggs are very small (microscopic) and do not have much yolk, so forces of 1 gravity are unlikely to effect them unless they have a specific gravity detection capability. Even more important, it would be very detrimental for mammalian embryos (other than those of monotremes such as platypuses) to depend on gravity in order to develop properly, because they are carried within their mother, which provides them with many advantages but also means that it is impossible to guarantee a constant direction of gravity in any but the largest mammals (and even these roll over occasionally) and impossible to guarantee even a predominant direction of gravity in highly active mammals such as tree-climbers and burrowing mammals. Therefore it seems highly likely that early mammalian embryonic development will be much affected by zero gravity unless the physiological state of the mother is altered too much. The upshot of all this is that if you want to eat pork or beef in space you need only have enough room to grow the animals (-: and some appropriate device to alleviate the obvious problems that will develop in a barn in zero-gravity :-), but if you want chicken or frog legs you are going to have to import these items or bring a centrifuge. 8-) -- | Lucius Chiaraviglio | ARPA: chiaravi@silver.bacs.indiana.edu BITNET: chiaravi@IUBACS.BITNET (IUBACS hoses From: fields; INCLUDE RET ADDR) ARPA-gatewayed BITNET: chiaravi%IUBACS.BITNET@vm.cc.purdue.edu Alt ARPA-gatewayed BITNET: chiaravi%IUBACS.BITNET@cunyvm.cuny.edu
jack@cs.glasgow.ac.uk (Jack Campin) (03/14/89)
In all this attention to foetal development, the mother seems to been forgotten about. Since bones lose a lot of calcium in zero-G, and pregnancy requires a lot of calcium for the baby, there may well be serious problems for her; and some of the chemical fixes that might prevent decalcification are hazardous to the foetus. -- Jack Campin * Computing Science Department, Glasgow University, 17 Lilybank Gardens, Glasgow G12 8QQ, SCOTLAND. 041 339 8855 x6045 wk 041 556 1878 ho INTERNET: jack%cs.glasgow.ac.uk@nss.cs.ucl.ac.uk USENET: jack@glasgow.uucp JANET: jack@uk.ac.glasgow.cs PLINGnet: ...mcvax!ukc!cs.glasgow.ac.uk!jack