Mark H. Bogart

Disruption of ovarian development in alligator embryos treated with an aromatase inhibitor

It has been suggested that sex differentiation in vertebrates is steroid hormone dependent, that estrogens play a critical role in ovarian differentiation, and that male sex differentiation will occur in the absence of estrogens. Using the model of the alligator in which sex can be manipulated by incubation conditions (eggs incubated at a constant temperature of 30 degrees produce 100% females, and at 33 degrees produce 100% males), a series of experiments using antiestrogens, antiandrogen, estradiol-17 beta, dihydrotestosterone (DHT), and aromatase inhibitors were performed. Test substances were injected into alligator eggs prior to gonadal sex differentiation and the eggs were incubated at male or female temperatures until just before expected date of hatching. Gonads were excised and the sex was verified histologically. Control embryos injected with vehicle produced the expected sex: females at 30 degrees and males at 33 degrees. Estradiol in eggs at 33 degrees (male temperature) produced 100% females and did not alter female development in eggs at 30 degrees. Antiandrogen, DHT, and a steroid antiestrogen had no discernible effect in either the 30 degrees or the 33 degrees eggs at the doses tested. The aromatase inhibitors aminoglutethimide and 4-hydroxyandrostenedione caused a moderate disruption of ovarian development and had no apparent effect on testicular development. The nonsteroidal aromatase inhibitor, Ciba Geigy 16949A, caused inhibition of ovarian development in all treated embryos. The Mullerian ducts did not appear to be affected by this treatment, or by any of the other treatments, and the gonads did not appear masculinized. We conclude that estrogen appears to be necessary for normal ovarian development, but that inhibition of estrogen synthesis alone is insufficient to cause masculinization. Likewise, exogenous androgens appear unable to masculinize embryonic gonads. The evidence suggests that testicular differentiation in amniote vertebrates is dependent on factors other than androgens or level of estrogens.

Sex determination: a hypothesis based on steroid ratios.

This paper presents a hypothesis for sex determination based on the ratio of androgen to estrogen in the gonad during sexual differentiation. In vertebrates the ratio of these steroids, and therefore, the sex of an individual is controlled by the quantity of the enzyme aromatase. For animals with a ZZ, ZW sex determining mechanism, such as birds, in which the heterogametic sex is female, an inducer for the aromatase gene is postulated to be on the W chromosome. In animals with an XX, XY system in which the heterogametic sex is male, such as mammals, the Y chromosome is postulated to code for a repressor of the aromatase gene. This hypothesis can account for naturally occurring sex reversal such as seen in some fish and amphibians, experimentally induced sex reversal by administration of steroids in birds, reptiles, fish and amphibians, and temperature-dependent sex determination as in reptiles. For invertebrates the same hypothetical model applies though the specific androgenic and estrogenic steroids differ. Both the X-to-autosome ratio method of sex determination typified by fruit flies and the haplodiploid method of bees as well as hormonal control of sexual differentiation in crustaceans are accounted for by this hypothesis.

Interstitial deletion of chromosome 2q associated with ovarian dysgenesis

In the present report we describe a girl with mental retardation, Dandy‐Walker malformation, craniofacial anomalies, cardiac defect, and ovarian dysgenesis associated with an interstitial deletion of chromosome 2. The interstitial deletion in the proband was associated with an apparently balanced translocation involving chromosomes 2 and 7 in the father.

Q-band polymorphism in a family of pygmy chimpanzees (Pan paniscus).

A polymorphic condition for the Q-band intense region of chromosome number 22 is identified in the pygmy chimpanzee (Pan paniscus). This polymorphism allows us to trace the pattern of inheritance of a number 22 chromosome in a family of pygmy chimpanzees. Previous Q-band findings are verified.

The production of mouse fetal-placental chimeras using trisomy 16 and euploid blastocysts.

SummaryBy means of a combination of immunosurgery and a modified method of microsurgery, blastocysts were reconstructed to produce viable chimeric fetal-placental units. Reciprocal reconstituted blastocysts were produced using euploid and trisomy 16 blastocysts. Reconstructed blastocysts yielded significantly smaller fetuses at day 17 of pregnancy than simultaneously transferred control blastocysts (mean body weight 0.49 g vs 0.64 g, P<0.01). However, apart from reduced size, no abnormalities were observed for any euploid fetus-euploid placenta construct. The three reconstructed blastocysts that yielded a trisomie fetustrisomic placenta were viable when examined on day 17 and displayed the abnormalities typical of mouse trisomy 16. No reconstructed blastocyst that yielded a trisomic fetus-euploid placenta or a euploid fetus-trisomic placenta was viable beyond day 13 of development. One case in which a trisomie fetus had a placenta that was chimeric (euploid/trisomic) examined on day 17 displayed the abnormalities typical of a trisomie fetus but the placenta appeared histologically normal. The findings suggest that there is a coordination of the development of the fetus and the placenta that is essential for the development of the fetus.

Overgrowth and Enlarged Heart in Mouse Fetuses with Maternally Inherited ThP and twLub2: An Example of Genomic Imprinting in Animals

ABSTRACT Thp/+ mouse is known to have differing phenotypes depending on gender of the ThP parent. In the present study, fetuses with maternally [Group A (until day 18 of pregnancy) and Group C (day 19)] and paternally [Group B] inherited ThP were examined with particular reference to the developmental abnormalities of hearts. In addition, a small number of fetuses with maternally inherited twLub2 on day 19 were compared with Thp. Group A ThP fetuses had greater body weight, possibly larger body size, generalized edema (100%), marked enlargement of the hearts (100%) and hypoplastic pulmonary trunk (73.7%). There were no such malformations in Group B ThP fetuses or in the controls (+/+) for both groups. The bilaterally thickened ventricular wall of fetal hearts in Group A and C ThP fetuses bulged into ventricular cavity. The pulmonary valve was also thickened. The labeling indices of the ventricular myocardial cells by BrdU were inclined to be higher in Group A ThP than in the control (+/+) fetuses. Fetuses of twLub2 had abnormalities of the cardiovascular system similar to Group C Thp. The results suggest that cardiac lesions in fetuses with maternally inherited ThP and twLub2 correspond to cardiomyopathy. Overgrowth and enlarged heart indicate the possibility of ThP as an animal model for Wiedemann‐Beckwith syndrome.