Ursula Mittwoch

PHENOTYPES AND GENOTYPES IN CYSTINURIA

Quantitative data are presented on the cystine, lysine and arginine excretion in patients with cystine stone formation and in their relatives in twenty‐five families.

Three cases of triploidy in man.

A premature baby of 32 weeks gestation and weighing 1.7 kg (3 lb 12 oz), with a defect in each iris and anomalous genitalia, showed XXY triploidy on chromosome analysis. Extensive blood grouping was consistent with both digyny and diandry, but the former was more likely. Two abortuses, received as part of a survey of spontaneous abortions, revealed XXX triploidy on tissue culture. One showed a fusion defect of the neural tube; both showed late or defective fusion of the embryonic cleft of the iris. In both a small proportion of nuclei in the amnion showed two Barr bodies. In two cases in which measurements of nuclear volume were made this was about 50% greater than in diploid controls.

THE PATTERN OF AMINO‐ACID EXCRETION IN CYSTINURIA

1. Cystine, lysine and arginine determinations have been carried out on urines from twenty‐eight cystinuric patients and 121 of their relatives. Urines from 250 unselected individuals have also been examined. The cystine was determined polarographically and the lysine and arginine microbiologically. The urines have also been examined for amino‐acids by two‐dimensional paper chromatography and by paper ionophoresis at pH 11‐5.

Sex differentiation in mammals and tempo of growth: Probabilities vs. switches

In the conventional model of sex differentiation in placental mammals, a switch is envisaged to steer the indifferent gonad into the path of either testicular or ovarian development. The immediate cause of the switch is thought to be the presence or absence of Sertoli cells, which in turn is controlled by the presence or absence of the testis-determining factor on the Y chromosome (TDF in humans, Tdy in mice). Quantitative investigations indicate, however, that the rate of growth of XY gonads is faster than that of XX gonads before the formation of Sertoli cells, and furthermore, that XY embryos develop faster than XX embryos long before the formation of gonadal ridges. Since the genetic constitution of the sex chromosomes appears to manifest itself from the earliest embryonic stages onwards, the concept of indifferent gonads being switched into alternate pathways becomes inappropriate. A model is proposed in which gonadal differentiation depends on developmental thresholds: the formation of Sertoli cells needs to occur by a particular stage in time in a sufficiently developed gonad, failing which the gonad will enter the ovarian pathway. While TDF is the principal factor enhancing the rate of gonadal growth, other factors which influence development rates can modulate the probability of a gonad becoming either a testis or an ovary.

Do Genes determine Sex

Chromosomes may control the duration of the cell cycle and the mitotic rate. Sex differentiation may be initiated by differential growth, and the human Y chromosome may increase the number of mitoses.

Males, Females and Hermaphrodites

Ancient myths of an hermaphrodite origin of man and his subsequent bisection into male and female individuals receive unexpected confirmation from the embryological evidence. The genital ridge contains the components to form either a testis or an ovary, while two sets of genital ducts are the forerunners of the male and female reproductive tracts. The presence of potentially hermaphrodite rudiments in different organisms resulted in the failure of attempts to formulate the determination of sex in terms of classical genetics. This, in turn, has led to the hypothesis that the function of the mammalian Y chromosome is to enhance the growth of the gonadal rudiment in male embryos. The hypothesis provides an explanation for the observed bilateral asymmetry of gonadal differentiation in human hermaphrodites in terms of the bilateral asymmetry of growth of human fetal gonads. The human condition can be related to the marked asymmetry of gonadal growth and differentiation in birds. The effect of temperature in the determination of sex in alligators has likewise been explained in terms of gonadal growth. The variety of sex‐determining mechanisms met with in vertebrates suggests a non‐sex‐specific effect adapted to specific biological needs. It is suggested that certain DNA sequences on the human Y chromosome act by enhancing the growth of somatic cells in the gonadal rudiment, leading to precocious differentiation of the testis.

Different Gene Expressions on the Left and the Right: A Genotype/Phenotype Mismatch in Need of Attention

Discordance in monozygotic twins has traditionally been explained in terms of environmental influences. A recent investigation has found a difference in epigenetic markers in older but not in younger twins. However, phenotypic differences that depend on an individuals postnatal life style do not address the problem of discordance in congenital malformations, or the reason why malformations are frequently unilateral, often with a preference for one or the other side. One such condition, cleft lip with or without cleft palate, which is preferentially expressed on the left, is a multifactorial condition, that is caused by a failure of the critical timing necessary for different groups of cells to meet and develop into a normal face. This process is dependent on cell proliferation and migration, which are energy‐dependent, while the additional requirement for apoptosis to allow cell fusion suggests the involvement of mitochondria. Recent progress in two separate areas of research could lead to a better understanding of the problem of facial clefts: (1) the recognition of an interaction between gene products and mitochondria in the aetiology of neurodegenerative diseases and (2) the discovery of an increasing number of genes, including transcription factors, growth factors and members of the TGF‐β signalling family, that are differentially expressed on the left and right side, thus pointing to a difference in their micro‐environment. These findings emphasize the importance of investigating the activity of candidate genes for complex developmental processes separately on the left and right sides. Data presented in this review suggest that differential growth rates may lead to an inversion of laterality. A method is described to test for a possible mitochondrial difference between left and right sides, using a mouse model with cleft lip.

Synaptonemal complex analysis in spermatocytes and oocytes of tertiary trisomic Ts(512)31H mice with male sterility

Whole-mount preparations of silver-stained spermatocytes and oocytes from Ts(512)31H mice were examined in the electron microscope. The 5(12) chromosome was associated with the XY bivalent in the large majority of spermatocytes, whereas in about one-half of the oocytes, the 5(12) was associated with either unpaired chromosomes or heterochromatic parts of chromosomes or showed self-synapsis. There was a tendency for 5(12) chromosomes to be more fully heterochromatic in oocytes than in spermatocytes. A large proportion of oocytes (50%) and a much smaller proportion of spermatocytes exhibited various errors of chromosome pairing, but these proportions were only marginally greater than in control gametocytes from mice with normal karyotypes. It is concluded that the observed errors of pairing bear no simple relation to the almost complete breakdown of spermatogenesis and the marked impairment of oogenesis that occur in tertiary trisomic Ts(5(12))31H mice.

Pachytene chromosomes in male and female mice heterozygous for the Is(7;1)40H insertion

Pairing of pachytene chromosomes was studied in oocytes and spermatocytes of mice heterozygous for the male-sterile Is(7;1)40H insertion using light and electron microscopy for synaptonemal complex analysis in surface-spread, silver-stained preparations. The data comprised four males and four female embryos. The insertion/deletion configurations appeared as either two bivalents or one quadrivalent in both sexes, but the proportion of bivalents was higher in oocytes. Some insertion and deletion bivalents showed synaptic adjustment. The insertion/deletion configurations were associated with, or adjacent to, the XY bivalent in the majority of spermatocytes. End-to-end association of different bivalents was more frequent in oocytes than in spermatocytes. It is suggested that physiological differences between male and female gametocytes may lead to the difference in their reproductive potential.

Pachytene pairing in relation to sperm and oocyte numbers in a male-fertile reciprocal translocation in the mouse

In adult males carrying the male-fertile reciprocal translocation T(2;4)13H, body weights, testis weights, and sperm counts were higher in heterozygotes than in homozygotes. Heterozygotes whose mothers were C3H/He exceeded their reciprocal counterparts in the same criteria. At 3-4 days of age, no significant differences between homozygous and heterozygous females were found in body weight, ovarian volume, or oocyte numbers, although mean oocyte volumes were somewhat larger in heterozygotes than in homozygotes. In homozygous males and females the synaptonemal complexes of rearranged chromosomes appeared as bivalents that were indistinguishable from normal bivalents. In most gametocytes of heterozygotes, the translocation was present in the form of a quadrivalent. The degree of pairing failure was greater in oocytes than in spermatocytes. Terminal asynapsis of quadrivalents was very rare in spermatocytes, but it affected one quarter of the oocytes. Only very few translocation configurations were associated with the XY bivalent. It is concluded that the number of sperm produced in male heterozygotes can match the general increase in vigor by the formation of a high level of fully paired quadrivalents, whereas a greater degree of terminal asynapsis in the quadrivalents of oocytes may indicate a slightly more deleterious effect of this translocation on oogenesis.