ACLARANDO TÉRMINOS

on chromosome I ; free granules of comparable size lay nearby yet the remainder of the nuclear

-132'- ëap was clear

6» In one newt there were swarims cf free granules in the immediate vicinity of the giant loops on

chromosome X, but not elsewhere (Figs#93 and 94)# Most normal lateral loops carry minute granules which are often barely visible with the light microscope^ In my o%)iniOn, these granules are regularly shed into the nuclear sap %irhere under favourable conditions they dissolve and their material passes into the cytoplasm. How let us suppose that there is a fall in the rate at which protein is being synthesised in the cytoplasm. As a result the transfer of materials from nucleus to cytoplasm would alow down but, for a time, metabolic activity in the hue l e w would remain unchanged* The produc# of lateral loop synthesis would accumulate in the nucleus* . Each loop

would continue to shed its granules, but those would not dissolve. Eventually a kind of "recrystallisation" and accretion of gone products would take place as a result of which granules would become larger and fewer in number. According to this scheme, granules are not a permanent feature of oocyte nuclei, and large free granules (more than Ip in diaemter) or large number^ of free granules are characteristic of nuclei whose anabolism is not

synchronised with synthetic processes in other parts of the cell. On the other hand, when an oocyte as a whole is intensely active, large masses of granular material may be shed from a

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neighbourhood of the locus* Newly eX&od granules would have to escape from this zone before they could dissolve la the nuclear sap, TXmus I account for the conditions illustrated in Figa#32, 03, and 04, and for the large numbers of mtlnute free granules wXiich lie amongst the chromosomes in the oocyte nuclei of gonadotrophin-treated newts, 1 would stress here that only once have I seen evidence to suggest that granules or lumps of material can detach from the giant loops of carnifex* and indeed the striking physiological variability at these loci ■points to the fact that in earn if e% the giant loops cannot regulate their size by a mechanism of this sort# No doubt the situation is different in criatatus and in T .viridescens

(Gall 1984) idiere it seems that largo bodies are regularly shed from the giant loops*

Callaa & Lloyd (I960) consider that objects visible with the light microseopo detach from lampbrusli chromosomes only

if they are being synthesised more rapidly than they are trans­ forming into nuclear sap* Ny own views this imtter are essentially in agreement with tXiOse of Callan & Lloyd, but I would suggest two qualifications. First, in T.criatatus large granules or bodies, more than Ip in diameter, may be shed from a few specific loci on the lampbrusXt cXiromosomes of oocytes which are intensely active. Secondly, the large free granules

commonly found iti the oocytes of unstimuluted newts are not

formed as such upon the chromosomes, although they do consist of gene product material.

"g

3.24—

While discussing the nature of free granules I have ' assumed that the RNA %irhieli tXiey contain will eventually take

part in the eynthesia of oytoplas(«ic proteins* This assumption is largely based upon evidence from autoradiography experiments of Ficq (1965) and Oallan and Gall (unpublished), which

showed a high rate of turnover of nuclear RNA in amphibian oocytes and a transfer of DMA from nucleus to cytoplasm* However, ï have also taken into account the results of some of my own experiments * For example, gonadotrophin treatment causes a disappearance of free granules from an oocyte nucleus, the formation of a cytoplasmic perinuclear zone of clear fluid, an increase in the concentration of cytoplasmic MMâ, and, as

judged by the rate of incorporation of , an increase in

Ï ' V-

the rate of protein synthesis in the egg cytoplasm. Brachet (1948) described an accumulation of HMA in the perinuclear

cytoplasm of growing oocytes* I have hot found evidence of such an accumulation in stained sections of nmft oocytes, but 1

consider that the perinuclear fluid which Ï have identified in fresh material may be significant in this respect*

Gall (1900b) drew attention to a likeness in the sizes of the RNP particles lAich are associated with the membranes of the endoplasmic reticulum (porter 1954, Palad© 1955) and those present on the normal lateral loops of lampbrush chromosomes. The particles which he describes are of the order of 300l in diameter, 1 do not know how these particles are related to the

• ' ■ . • . • . . ■■ . ' \ ■■ 'T .V tV

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granules which one can see with the light microscope and I do

not proposé to discuss this matter here# j

Hitherto I have rather presumptuously used the word j "dogma" i^hen referring to Current views on the origin of oocyte 1

:i "nucleoli**, and in %iQr introduction to Chapter 111, 1 placed ^

' i

much of the responsibility for this standpoint upon Gall (1954, ^ 1058), % own views about the origin of oocyte nucleoli are

reactionary, and presently 1 shall muster more facts to sup%)ort ^ these views# To begin with however, I must amke Clear that I 4

think one or other' of the more conspicuous object# which one 1

finds attached laterally to the lampbrush chromosomes of earn if ex .2

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