Notes to Chapter 6

¹Similar syndromes have been reported in mink ( Padgett et al., 1964), cattle ( Padgett et al., 1964), cats ( Kramer et al., 1977), and in a killer whale ( Taylor and Farrell, 1973). In mink and cattle the condition has been conclusively shown to be inherited as an autosomal recessive and this appears to be the case in cats, too. (For reviews see Padgett 1968; Padgett et al., 1970; Davis and Douglas, 1972; Windhorst and Padgett, 1973; Prieur and Collier, 1978).

²Patients with Chediak-Higashi syndrome also often display a widespread mononuclear infiltration of organs resembling lymphoma that is referred to as the accelerated or malignant phase. They also may display peripheral granulocytopenia, defective granulocyte regulation, and intermedullary granulocyte destruction ( Blume et al., 1968).

³Children suffering from the Chediak-Higashi syndrome display either a decrease or absence of uveal pigment and there is a marked photophobia. "The hair is pale gray, blond, or brunette with a distinctive overcast and streaks of gray. The skin is generally pale, but on the exposed parts of children born of dark-skinned parents it may have "slate-gray" coloration or hyperpigmentation" ( Windhorst et al., 1966). Electron microscopy of hair bulb melanocytes disclosed the "the granules were large and numerous. Each granule was limited by a single membrane and contained a number of strands which made up the granule matrix. The melanosome granules were 2 to 3 times as thick and approximately twice as long as normal melanosomes. The large granules contained approximately twice as many strands as are normally found within a matrix of pigment granules, and in some instances the strands appeared to be more irregular than those found in the typical matrix of melanosomes. Melanin was present, although its relative concentration on the larger melanosomes may have been less than it is in fully developed, normal melanosomes" ( Windhorst et al., 1966). In a study aimed at examining the formation of massive melanosomes of the disease, and the basis of the hypopigmentation, Zelickson et al. ( 1967) concluded that the giant particles appear to originate from defective premelanosomes, and that the continued growth and/or fusion of these premelanosomes eventually results in enormous particles which degenerate. It is believed that although the destruction of these giant melanosomes may dilute the color of the skin, that a more likely basis for the hypopigmentation is the abnormal packaging of normal sized melanosomes into large lysosome-like structures in the epidermal cells. An examination of the eye of affected individuals "revealed relatively normal (though fewer) granules in the choroid, with grossly deficient melanin granules of the retinal pigmented epithelium." Moreover, in these granule-deficient areas of the retina the melanin granules were abnormally large ( Windhorst et al., 1968). As a consequence of these observations, Windhorst and her colleagues ( 1968) conclude "that the basis for the pigmentary anomaly of the Chediak-Higashi syndrome can best be regarded in terms of a structural abnormality of the melanosome, perhaps in the lipo-protein building blocks that are thought to be common to all membranes."

⁴Lutzner et al. ( 1967) report that the giant melanin granules of the beige mouse range from 2 to 10 microns.

⁵The coats of B^lt/B^lt;bg/bg mice resemble the "blue" coat of animals homozygous for both bg and d, but have a somewhat less silvery appearance, presumably due to greater amounts of pigment in the hair tips ( Pierro, 1965)

⁶Poole and Silvers (unpublished) also have observed that A^y/a;bg^J/bg^J mice can be distinguished from normal yellow animals because their coats are slightly more dilute, especially on the belly and at the base of the hairs.

⁷Lutzner ( 1970) and Lutzner and Lowrie ( 1972) also have studied the fine structural development of beige granules and their observations are similar to those of Hearing et al. They found that the earliest observable melanin granules in the retina and choroid of beige embryos were larger than those in C57BL/6 (+/+) "controls." "Granule membranes were disrupted and melanosome fibers were surrounded by vacuolar spaces. In older beige embryos giant granules were seen with a central nidus of normally formed cylinders surrounded by layers of melanin fibers, exhibiting a spectrum of maturity with the least mature fibers towards the periphery [see Figure 6-3d]. Premelanosomes appeared to be fusing to the outside of these giant granules" ( Lutzner, 1970). Lutzner and Lowrie also observed that the giant granules in adult beige melanocytes are composed predominantly of fully melanized structures. Concentric rings were often seen in abnormal granules which could represent waves of melanization (see Figure 6-3a). While in some adult melanocytes both normal premelanosomes and melanosomes occur along with fully mature giant granules, in others almost the entire cytoplasm appears filled with maturing giant granules. From these observation Lutzner and Lowrie suggest "that the giant beige melanin granule is formed through the continual deposition of melanofilaments by granule fusion and/or failure of size-control mechanisms."

⁸In bg^J/bg^J;p/p mice, no giant granules were observed in the retina and 2% of the choroidal granules were giants ( Hearing et al., 1973).

⁹The mast cells of beige mice also display giant granules ( Chi and Lagunoff, 1975; Chi et al., 1978). Indeed, the fact that beige mice possess giant granules in a variety of cells has been employed as a cell marker. Thus, it has been used as a neutrophil marker to study the kinetics of bone marrow replacement in anemic W/W^v [see Chapter 10, section I(G)] mice ( E. Murphy et al., 1973; Maloney et al., 1978; Patt and Maloney, 1978). It also has been used to investigate the origin of mast cells ( Kitamura et al., 1977; see Chapter 10, note 27).

¹⁰J. Vassalli et al. ( 1978) have reported that the polymorphonuclear leukocytes of patients with Chediak-Higashi syndrome are profoundly deficient in elastase and that the corresponding murine protease is similarly decreased in the leukocytes of beige mice. They suggest in the case of the human syndrome that this deficiency may account, at least in part, for the high incidence of infections.

¹¹Excretion into the urine is a major mechanism by which lysosomal enzymes are removed from the normal mouse kidney and Brandt and his associates propose that this process is impaired in bg/bg mice because of an abnormal fusion of lysosomes with the plasma membrane of the kidney proximal tubule cells. Recently Novak and Swank ( 1979) have reported that other coat-color determinants also affect kidney lysosomal enzyme concentrations. Thus, pale ear ( ep/ep), pearl ( pe/pe), and pallid ( pa/pa), like beige ( bg^J/bg^J), produce a 2.5-fold increase in the concentration of kidney beta-glucuronidase; maroon ( ru-2^mr/ru-2^mr) and ruby eye ( ru/ru) produce a 1.6- to 1.8-fold increase; and light ( B^lt/+), dominant spotting ( W/+), extreme nonagouti ( a^e/a^e), slight dilution ( d^s/d^s), and himalayan ( c^h) produce a smaller (about 1.3-fold) but still significant increase in the concentration of this enzyme. Further characterization of the three mutants, ep/ep, pe/pe, and pa/pa, indicated that, like bg^J/bg^J, they have a generalized effect on lysosomal enzymes since they display coordinate increases in kidney beta-galactosidase and alpha-mannosidase (these enzymes also are increased in the kidneys of maroon and ruby-eye mice). The effects of these three deviants appear to be lysosome specific since rates of kidney protein synthesis and activities of three nonlysosomal kidney enzymes proved normal. The influence of these genes also appears to be relatively tissue specific since all were associated with normal liver lysosomal enzyme concentrations. A common dysfunction in all three mutants was a decreased rate of lysosomal enzyme secretion from kidney into urine. Whereas normal C57BL/6J animals daily secreted 27 - 30% of total beta-glucuronidase and beta-galactosidase, secretion of both these enzymes was coordinately depressed to 1 - 2, 8 - 9, and 4 - 5% of total kidney enzyme in ep/ep, pe/pe and pa/pa mice, respectively. Although depressed lysosomal enzyme secretion appears to be a major influence of these coat-color determinants, Novak and Swank also found that the synthetic rate of kidney glucuronidase was increased 1.4- to 1.5-fold in pearl and pallid animals. As pointed out by Novak and Swank, taken together these observations "reinforce the histochemical and biochemical similarities reported between lysosomes and melanosomes and suggest that there may be many steps in common in the control of subcellular organelles."

¹²The basic biochemical defect in the Chediak-Higashi syndrome also remains to be elucidated. However, recent studies indicate that in this condition, too, there is a microtubular defect which appears correctable by treatment with cyclic guanosine monophosphate, cholinergic agonists ( J. Oliver, 1976), or ascorbate ( Boxer et al., 1976). For other investigations on the beige syndrome see Prieur et al. ( 1972), Chi et al. ( 1975, 1976), Holland ( 1976), J. Oliver et al. ( 1976), Frankel et al. ( 1978), Guy-Grand et al. ( 1978), Kaplan et al. ( 1978), Lyons and Pitot ( 1978), and Swank and Bradt ( 1978).

¹³In addition to silver, Hagedoorn studied the interactions of a number of other coat-color factors. His 1912 paper is particularly entertaining because it includes a color plate of 24 charmingly drawn mice, each displaying a different phenotype.

¹⁴In outcrosses, silver is nearly, though not quite, recessive as some heterozygotes may display a few white hairs, mainly on the belly ( Dunn and Thigpen, 1930; Grüneberg, 1952).

¹⁵However, whereas all light hairs are pigmented at their tips many hairs in silver animals are unpigmented or banded with pigment.

¹⁶On the basis of the pigment patterns displayed by allophenic mice (see Chapter 7), Mintz ( 1971a) suggests that si/si genotypes express hair follicle clonal patterns. If this is the case it would place the site of action of si in the skin and not the melanocyte.

¹⁷LaVail and Sidman ( 1974) report that the slightly diluted pigmentation of the juvenile coat of le/le mice becomes darker in adults. They also found the eye pigmentation of these mutants to be altered. The melanosomes of the retinal epithelial cells were fewer and usually smaller than those in +/le mice. There also were fewer melanosomes in the choroidal melanocytes of homozygotes, and these were, on the average, larger, much more heterogeneous in size, and less densely packed than those in +/le melanocytes. The diameters of some of these le/le granules were three to four time those in +/le eyes. le homozygotes also appear to have fewer choroidal melanocytes and in newborns these are restricted to the anterior regions of the eye. During the first 2 weeks after birth, however, melanocytes come to occupy progressively more posterior parts of the eye. Finally, it should be noted that light ear, like pale ear (see note 11), has a striking effect on lysosomes in the kidney. Thus, males homozygous for le display a 4-fold elevated concentration of kidney beta-galactosidase. They also have a decreased secretion of kidney beta-hexosaminidase but in this case there is no significant accumulation of this enzyme in the kidney ( Meisler, 1978).

¹⁸In 1957 Pizarro briefly described a recessive gene which he called platino ( pl) and which appeared to be a mimic of extreme dilution ( c^e). This determinant, which was not allelic to c, produced a very light-colored phenotype with dark eyes. The number of pigment granules in the hair was greatly reduced. As far as I am aware this mutation is no longer maintained.