Endodermal secretion of chitin in the 'cuticle' of the earthworm gizzard

The gizzard of earthworms is definitely of endodermal origin. Contrary to the opinion that tissue of endodermal origin is unable to synthesize chitin, the gizzard epithelium secretes large amounts of chitin-containing material which has special properties. 28.7 +/- 5.7% of the dry weight proved to be chitin; the microfibres form a random felt-like texture. They are not arranged in layers comparable to those found in arthropod cuticle. The protein content amounts to 44.9 +/- 7.1% of the dry weight; the remaining material contains at least uronic acids. In the protein matrix large amounts of the enzymes amylase and protease have been demonstrated. As the so-called cuticle is sloughed off at the lumen side, these enzymes are mingled with the gut contents. It might be called a gastric shield, as it closely resembles this structure, widespread among Mollusca. The thickness of the gizzard cuticle varies between 10 and 90 mum in Lumbricus terrestris and 10-50 mum in L. rubellus. Autoradiography has shown that it is replaced at a high rate. In Lumbricus terrestris it is renewed completely in less than 60 hr, and in smaller Lumbricus rubellus, this takes place in about 48 hr. These results are in agreement with the biochemical findings.     

The use of drugs to dissect the pathway for secretion of the glycoprotein hormone chorionic gonadotropin by cultured human trophoblastic cells

Agents that affect intracellular cation and pH gradients and inhibit energy production have been tested for their ability to modulate the processing and secretion of the free alpha subunit and the alpha beta dimer of human chorionic gonadotropin (hCG) by cultured human trophoblastic cells (JAR). Incubation of JAR cells with monensin or nigericin, monovalent cation ionophores that produce equilibration of Na+ and K+ across cellular membranes, dicyclohexylcarbodiimide, an agent that inhibits intracellular membrane ATPases, and methylamine, which neutralizes intracellular pH gradients, produced similar effects on hCG processing and secretion. All these agents inhibited the processing of the asparagine-linked oligosaccharide chains of free alpha subunit and the alpha and beta subunits contained in the hCG dimer. Moreover, after treatment of JAR cells with these agents, there was an intracellular accumulation of precursor forms and an inhibition of secretion of "mature" forms of hCG. Monensin affected the processing and secretion of hCG subunits differently at different concentrations. At 5 X 10(-7) M, monensin inhibited the processing of the asparagine-linked oligosaccharides of hCG without altering the rate-limiting step in the secretory pathway or blocking hCG secretion. The intracellular hCG subunit precursors in both control and monensin-treated cells contained a similar array of high mannose oligosaccharides, predominantly of the Man8GlcNAc2 and Man9GlcNAc2 types. However, monensin-treated cells secreted hCG subunits that contained endo H-sensitive oligosaccharides of the high mannose (mostly Man5GlcNAc2) and hybrid types rather than the endo H-resistant complex chains synthesized by control cells. Nevertheless, a full complement of serine-linked oligosaccharides was added to the hCG-beta subunit in monensin-treated cells. These results indicate that the intracellular movement of hCG from the rough endoplasmic reticulum to the cell surface was not inhibited by monensin at a concentration that impaired Golgi-localized steps in the processing of asparagine-linked oligosaccharides. At 5 X 10(-6) M, monensin significantly inhibited secretion of hCG and created a new rate-limiting step in the processing pathway. hCG subunits bearing Man5GlcNAc2 units accumulated intracellularly, suggesting that the equilibration of intracellular Na+/K+ pools blocked oligosaccharide processing at an intra-Golgi point, perhaps by inhibiting movement of the glycoprotein hormone from the "cis" to the "trans" Golgi compartment. Since the other drugs mentioned above produced similar effects on hCG processing and secretion, it appears that maintenance of intracellular cation and pH gradients is necessary for the intra-Golgi transport of glycoprotein hormones.(ABSTRACT TRUNCATED AT 400 WORDS)     

Genetic control of murine hemagglutinin formation to H-2.5

When B10.D2 (H-2^d) mice are immunized with lymphoid cells from C57B1/10 (H-2 ^d ) and their antisera tested against B10.A (H-2 ^a ) target cells, only antibodies to H-2.5 are measured. The same is true for immunization of DBA/2 (H-2 ^d ) mice when their antisera are absorbed with B10.D2 cells prior to testing. Irrespective of the dose of immunogen administered, the primary hemagglutinin response of B10.D2 mice is significantly lower than that of DBA/2 mice and (B10.D2 × DBA/2)F₁ hybrids, but the secondary responses are similar. The low responsiveness of B10.D2 mice appears to be determined by a single dominant gene with incomplete penetrance; the gene is not linked to eitherH- 2, Hc, or the immunoglobulin allotype loci. In addition, the H-2.5 hemagglutinin response is susceptible to nongenetic influences. When antisera from B10.D2, devoid of H-2.5 hemagglutinins, were assayed in a complement-mediated cytotoxic test, they contained almost as much anti-H-2.5 activity as did the antisera from DBA/2 mice or (B10.D2 × DBA/2)F₁ hybrids. The possibility is discussed that the locus responsible for the deficient primary hemagglutinin response of B 10.D2 may not be determinant-specific but may affect hemagglutinin responses in general.     

Inheritance of asymmetry inKrizousacorixa femorata (Guérin)

Krixousacorixa femorata (Guérin), a Mexican corixid, has symmetrical females and asymmetrical dextral or sinistral males. In studying the genetics of this species a sequence of experimental matings is described and the segregation ratios of the progenies analyzed. On the basis of these experiments a hypothesis, adequately explaining the data, is proposed.Exhypothesi the inheritance of the polymorphic characteristic of asymmetry depends upon the allelomorphic series of three genes,D, D ⁸, andd, of whichD (dextrality) is dominant toD ^s (sinistrality) which in turn is dominant tod (dextrality). The intermediate member of the series is lethal as a homozygote.A portion of the dissertation submitted in partial fulfillment of the requirements for the doctorate at Cambridge University. I wish to thank Professors SirRonald Fisher of Cambridge University andG. E. Hutchinson of Yale University for their kind help.