Thyroid hormone-dependent gene expression program for Xenopus neural development.

Although thyroid hormone (TH) plays a significant role in vertebrate neural development, the molecular basis of TH action on the brain is poorly understood. Using polymerase chain reaction-based subtractive hybridization we isolated 34 cDNAs for TH-regulated genes in the diencephalon of Xenopus tadpoles. Northern blots verified that the mRNAs are regulated by TH and are expressed during metamorphosis. Kinetic analyses showed that most of the genes are up-regulated by TH within 4-8 h and 13 are regulated by TH only in the brain. All cDNA fragments were sequenced and the identities of seven were determined through homology with known genes; an additional five TH-regulated genes were identified by hybridization with known cDNA clones. These include five transcription factors (including two members of the steroid receptor superfamily), a TH-converting deiodinase, two metabolic enzymes, a protein disulfide isomerase-like protein that may bind TH, a neural-specific cytoskeletal protein, and two hypophysiotropic neuropeptides. This is the first successful attempt to isolate a large number of TH-target genes in the developing vertebrate brain. The gene identities allow predictions about the gene regulatory networks underlying TH action on the brain, and the cloned cDNAs provide tools for understanding the basic molecular mechanisms underlying neural cell differentiation.

A mechanism for virilization of female spotted hyenas in utero.

Female spotted hyenas exhibit male-like genitalia and dominance over males. Hyena ovarian tissues incubated in vitro produced large quantities of the steroid hormone precursor androstenedione. The activity of aromatase, which converts androstenedione to estrogen, was one-twentieth as great in hyena versus human placental homogenates. In comparison, the activity of 17 beta-hydroxysteroid dehydrogenase, which converts androstenedione to testosterone, was equal in the two homogenates. The limited aromatase activity may allow the hyena placenta to convert high circulating concentrations of androstenedione to testosterone, which results in virilization of the fetal external genitalia and possibly destruction of fetal ovarian follicles. Androstenedione production by residual ovarian stromal cells during reproductive life accounts for the epigenetic transmission of virilization in female spotted hyenas.

Inhibition of in vitro pituitary gonadotropin secretion by 17 beta-estradiol in the frog Rana pipiens.

We tested the effects of low concentrations of 17 beta-estradiol (E2) on the in vitro pituitary responsiveness to gonadotropin-releasing hormone (GnRH) in frogs (Rana pipiens). We first showed that the pH indicator phenosulfonpthalein (phenol red, PR) at levels normally used in the culture medium did not significantly affect pituitary basal or GnRH-stimulated gonadotropin secretion in male glands, as may occur in mammals. Incubation of male glands with E2 at 10 pg/ml for 24 hr in medium lacking PR did not alter basal follicle-stimulating hormone (FSH) or luteinizing hormone (LH) secretion, but significantly attenuated responsiveness of both gonadotropins to GnRH (0.2, 1, and 5 ng/ml); E2 did not affect responses at the highest dose of GnRH (25 ng/ml). GnRH responsiveness of female pituitaries was also inhibited by E2 at all doses of GnRH; 1 ng/ml E2 had greater effects than did 10 pg/ml. The present results demonstrate that E2 at concentrations commonly found in the circulation of both sexes have a consistent direct inhibitory effect on FSH and LH secretion at the level of the pituitary.

Hormonal correlates of 'masculinization' in female spotted hyaenas (Crocuta crocuta). 1. Infancy to sexual maturity.

This report is concerned with hormone concentrations accompanying sexual maturation in a highly 'masculinized' female mammal, the spotted hyaena, Crocuta crocuta. Plasma concentrations of testosterone, androstenedione and oestrogen were determined by radioimmunoassay in a longitudinal study of 12 female and eight male hyaenas 2.5-62.5 months old. Concentrations of testosterone were significantly higher in males than in females after 26.5 months of age, but earlier measurements did not differ between sexes. Mean testosterone concentrations in adult female hyaenas (0.4-0.5 ng ml-1) were similar to those in several other female mammals that do not display a 'masculine' profile, but mean concentrations of androstenedione (2.5-5.5 ng ml-1) in female hyaenas were significantly higher than in males (1.0-2.0 ng ml-1), at most ages. Oestrogen could not be detected (less than 0.03 ng ml-1) in females until about 14 months of age and then increased (to approximately 0.13 ng ml-1) between 18 and 30 months; oestrogen remained undetectable in males. This rise in oestrogen in females corresponded to nipple enlargement and to changes in the size and elasticity of the urogenital meatus, permitting copulation and parturition through the clitoris. Gonadectomy (two males and four females) at 4-7 months resulted in nondetectable concentrations of testosterone and oestrogen and a marked attenuation in androstenedione (to approximately 0.39 ng ml-1), indicating that the gonads are the major source of these three steroids. Gonadectomy also eliminated sex differences in weight, nipple development and elasticity of the urogenital meatus.

Hormonal correlates of 'masculinization' in female spotted hyaenas (Crocuta crocuta). 2. Maternal and fetal steroids.

Concentrations of androgens (androstenedione, testosterone, 5 alpha-dihydrotestosterone), oestrogen and progesterone were measured in relation to pregnancy in the spotted hyaena (Crocuta crocuta). The gestation period was estimated to be about 110 days. There was a marked progressive rise in all the steroids starting in the first third of gestation. Chromatographic separation of plasma showed that much of the oestrogen is not oestradiol (only 12% of total measured) and that a significant fraction of the 'testosterone' may be dihydrotestosterone. In the final third of pregnancy, concentrations of androgen (especially testosterone plus dihydrotestosterone) in the female circulation reached the maximal values of adult males; the percentage of dihydrotestosterone relative to total testosterone plus dihydrotestosterone was higher in females (44 +/- 3.9%, n = 20) than in males (29.5 +/- 3.5%, n = 17). Plasma androstenedione was also significantly higher in females, but the increment was less than for oestrogen, testosterone and progesterone, and the temporal pattern was less clear. Samples from the maternal uterine and ovarian circulation showed that androstenedione is largely of ovarian origin and metabolized by the placenta, while testosterone, progesterone and oestrogen are primarily of placental or uterine origin. Fetal samples were taken from two mixed-sex sets of twins and one male singleton. Gradients across the placenta measured in the fetal circulation confirmed that the placenta metabolizes androstenedione and is a source of testosterone for the female fetus; there were no consistent differences in androgens between male and female fetuses. It is suggested that the conspicuous masculinization of the female spotted hyaena, especially evident in the external genitalia at birth, is a result, at least in part, of high placental production of testosterone or dihydrotestosterone derived from the metabolism of high maternal androstenedione.

Identification and purification of a high-affinity thyroxine binding protein that is distinct from albumin and prealbumin in the blood of a turtle, Trachemys scripta.

Fractionation of plasma proteins in the turtle, Trachemys scripta, confirmed the presence of a high-affinity thyroxine (T4) binding protein (TBP) that was distinct from albumin (ALB) and prealbumin (PA). The TBP was isolated by adsorption on a T4-affinity column and a high degree of purification was achieved by gel filtration and preparative electrophoresis. Analysis by reversed-phase HPLC showed a single peak of protein with T4 binding activity. The electrophoretic mobility of the TBP, based on staining and binding to [125I]T4 on nondenaturing polyacrylamide gels (PAGE), corresponded to that of the major T4 binding activity previously identified in plasma (ca. 60 kDa). PA was fractionated as a complex with retinol binding protein (PA-RBP) based on retinol associated fluorescence using ion exchange chromatography on DEAE-Sephacel and gel filtration. This complex behaved as a larger and more highly charged molecule than TBP; it was partially dissociated in low ionic strength basic solution. SDS-PAGE of the PA-RBP-enriched fraction revealed a major component of about 48 kDa (possibly free PA), with smaller components corresponding to those expected for free RBP (ca. 22 kDa) and subunits of PA (e.g., 14 and 28 kDa). ALB was purified by ion exchange chromatography on DEAE and gel filtration; it behaved as less basic than PA with MW approximately 67 kDa. TBP accounted for virtually all the T4 binding activity of whole plasma: TBP was about 100 times as active and PA and ALB were less than 1% as active as plasma. The binding affinity of purified TBP was similar to that of whole plasma from turtle and human (e.g., approx. 10(9) M-1 on Sephadex G-25).

Measurement of plasma thyroxine binding protein in relation to thyroidal condition in the turtle, Trachemys scripta, by radioimmunoassay.

Polyclonal (rabbit) antisera were generated against a high-affinity plasma thyroxine (T4) binding protein (TBP) purified from the turtle, Trachemys scripta, and used to develop a specific radioimmunoassay (RIA). The RIA demonstrated the presence of an immunochemically related protein in the plasma of several other species of Trachemys and in members of several other genera from the same family, Emydidae. Plasma from all nonemydids and some emydid genera either showed no competition or nonparallelism in RIA. The presence and level of radioimmunoassayable TBP in diverse species correlated with results of previous comparative measurements of T4 binding activity. However, an immunoreactive protein of the same molecular weight as TBP was identified in all turtles by Western blot analysis. More detailed studies in T. scripta demonstrated that variations in plasma T4 binding activity induced by experimental or environmental manipulations were related to differences in TBP concentrations. The concentration of TBP varied by orders of magnitude (from less than 1 to ca. 150 mg/liter) in euthyroid animals; levels showed ontogenetic changes (virtually absent in hatchlings) and were directly related to thyroidal status. Experimentally induced hypothyroidism (goitrogen treatment or surgical thyroidectomy) resulted in a marked suppression of TBP, and T4 treatment prevented its decline or reinstated it. Thus, in the turtle, this T4 transport protein may exist in higher concentrations and its levels are more variable and show a different relationship to thyroid activity than the analogous T4 binding globulin (TBG) in mammals.

The role of hormone binding in the cold suppression of hormone stimulation of the pituitary, thyroid, and testis of the turtle.

The ability of hormones to bind to their functional receptors on turtle (Pseudemys scripta) endocrine target tissues in the cold was tested by treating tissues with secretagogues at low temperatures (5-15 degrees) and then following subsequent target stimulation in the absence of secretagogue at a warm temperature (28 degrees). Administration of thyrotropin-releasing hormone (TRH), corticotropin-releasing hormone, and growth hormone-releasing hormone to pituitaries at low temperatures (20 degrees or below) suppressed responses in growth hormone (GH) and thyrotropin (TSH) secretion and there was little or no response in pituitaries subsequent to warming. In contrast, gonadotropin-releasing hormone treatment of pituitaries, TSH treatment of thyroid glands, and gonadotropin (FSH and LH) treatment of testes in the cold (down to 5 degrees) was followed by a large response in the target glands (secretion of LH, thyroxine, and testosterone (T), respectively) following warming. Additional studies with FSH and LH showed that these hormones can bind to testes rapidly (within 5 min) at low temperatures where no acute response is observed, although the dose sensitivity and the extent of this priming in the cold are less than at warm temperatures. Thus, postreceptor events may be more important than binding per se for temperature effects on hormone responses of tissues, but even this component of cell function varies among tissues. The effects of a receptor-independent secretagogue (tetraethylammonium chloride), which causes cell depolarization by blocking K+ efflux, were also blocked at low temperatures in thyrotropes and somatotropes but not in gonadotropes. Rapid depressions in TSH and GH secretions following cooling of TRH-stimulated pituitaries and of T secretion in LH-stimulated testes provide further evidence for cold sensitivity of postreceptor processes in these tissues.

Steroidal modulation of pituitary gonadotropin-releasing hormone responsiveness in young turtles, Pseudemys scripta.

Steroid-modulated pituitary secretion and glandular content of gonadotropin (Gth: LH and FSH) was studied in young slider turtles. Injection (ip) of both 17 beta-estradiol (E2) and testosterone (T) reduced pituitary content of both Gths and caused significant inhibition of basal LH secretion and gonadotropin-releasing hormone (GnRH)-stimulated LH and FSH secretion measured in vitro. However, gonadectomy did not affect pituitary Gth secretion or response in these juveniles, and anti-estrogen and anti-androgen compounds had some steroid agonistic action on the pituitary gland. Exposure to E2, T, and 5 alpha-dihydrotestosterone (DHT) in vitro for 4, 24, or 48 hr either had no effect or completely inhibited pituitary GnRH responsiveness. Progesterone (P) alone had no effect on pituitary GnRH response and in combination did not alter the typical inhibitory effect of E2. There were several indications of differential effects of steroids on secretion of the two Gths, especially in response to GnRH and tetraethyl chloride (receptor independent) stimulation. The results suggest that steroids may act directly at the pituitary level to alter Gth secretion and that steroidal modulation of pituitary secretion might play a role in differential regulation of LH and FSH in turtles.

[Socioeconomic determinants of migration in Mexico]. / Determinantes socioeconomicos de migracion en Mexico.

"This study examines the socioeconomic influence on migration frequency and transitory movements in four Mexican regions. The analysis is based on data gathered from the [Mexican Fertility Survey] 1976-1977, considering the influences of...education, occupation, literacy, place of residence and fertility. The methods used for this analysis were regression and logistic regression." Aspects considered include patterns of internal migration in Mexico, data sources, analysis of independent variables, migration experiences, and age effects. A comment by Carlos Brambila Paz is included (pp. 179-83). (SUMMARY IN ENG)

Temperature dependence of in vitro pituitary, testis, and thyroid secretion in a turtle, Pseudemys scripta.

In vitro culture was used to examine the direct actions of temperature at the level of pituitary hormone [luteinizing hormone (LH), thyrotropin (TSH), growth hormone (GH), prolactin (PRL)] responses to neuropeptides and two related peripheral endocrine responses [thyroid hormone (T4) and testicular androgen secretion] to pituitary hormones (TSH and gonadotropins) in a turtle, Pseudemys scripta. All these responses were fully suppressed at very low temperatures (5-6 degrees) and maximal near the species' preferred body temperature (28 degrees), but sensitivities differed markedly in intermediate ranges. At the pituitary level, the response of TSH, GH, and PRL to thyrotropin-releasing hormone (TRH) was considerably more temperature sensitive than the response of LH to gonadotropin-releasing hormone (GnRH) stimulation. TSH, GH, and PRL were unresponsive at 20 degrees or below, whereas LH secretion was stimulated almost equally between 12 and 28 degrees; the main effect of cooling on LH secretion was to reduce the duration of the response to GnRH. There was no clear effect of previous thermal history on temperature sensitivity of pituitary neuropeptide responsiveness although the general responsiveness of the gland was altered; however, these latter effects may also be related to variations in other factors such as photoperiod, season, and nutrition. Temperature sensitivities of the thyroid and testes also differed, but in the opposite way from the related pituitary cell types. Thyroid glands were relatively insensitive to temperature and responded to TSH between 12 and 32 degrees, with no difference between 20 and 28 degrees. In contrast, testicular androgen secretion showed an abrupt decline in gonadotropin responsiveness below 28 degrees; dose sensitivity, response rate, and maximal output were affected. Results were similar for sea turtle LH, snapping turtle LH, and ovine follicle-stimulating hormone. Thus, the temperature dependence of the two endocrine systems may have a different rate-limiting component.

Effects of gonadectomy and steroids on pituitary gonadotropin secretion in a frog, Rana pipiens.

Secretory dynamics of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were measured at various times following gonadectomy in adult male grass frogs, Rana pipiens. Plasma levels and in vitro initial secretory rates of both LH and FSH increased significantly within 1 wk and remained elevated for 3-4 wk of castration. Pituitary FSH and LH content were unchanged. However, dissociation between the two gonadotropins (Gth) occurred thereafter: Secretion of FSH remained elevated for 70 days, but those of LH declined to control levels after 30 days. In vitro secretion of Gth from gonadectomized (gonadx) frogs declined progressively over time reaching control levels after 24 h incubation. The results indicate that elevated pituitary secretion contributes to the observed circulating LH and FSH levels in gonadx frogs, and that FSH and LH may be controlled independently. Replacement therapy with 17 beta-estradiol (E2) suppressed post-gonadectomy increases in plasma Gth and in vitro responses to GnRH, whereas 5 alpha-dihydrotestosterone (DHT) had little effect in vivo and augmented GnRH responses in long-term castrates. In vitro, E2 also inhibited, while 48 h of DHT treatment had no effect on GnRH responsiveness of pituitaries from gonadx frogs. The actions of these steroids were opposite to those typically observed in mammals (and birds), and support the hypothesis that E2 may contribute to seasonal testicular regression in ranid frogs.

Socioeconomic determinants of fertility: selected Mexican regions, 1976-1977.

PIP: Cumulative fertility is analyzed for 4 regions of Mexico, based on World Fertility Survey data of 1976-77; the state of Baja California, the Northwest region, the State of Jalisco, and the Northeast region. Based on stepwise regression methodology, the study compares results for 12 subsamples of married respondents, 3 age categories by 4 regions. The dependent variables are children ever born and children ever born in the last 5 years. Migration, urban, educational, and occupational variables are included as independent variables. Regression results reveal level of education is the major, and negative, influence on fertility. Other results include specific negative effects for prior occupation, size of place of residence, and childhood place of residence. Fertility effects appear different for migration origin and destination regions, but more similar for younger ages. Effects of migration on fertility are small. Mean fertility as measured by children ever born was 4.34 for the 1976-77 World Fertility Survey samples versus 3.69 for the Mexican census of 1980. Fertility varied somewhat by region with the highest and lowest values in Jalisco and the Northeast, respectively. Expected age-related changes in fertility were noted.^ieng

Photoperiodic time measurement in seasonal reproduction of the weaver bird (Ploceus philippinus).

Use of a circadian clock in photoperiodic time measurement is demonstrated in the tropical photoperiodic weaver bird with the help of resonance, ahemeral, and asymmetrical skeleton photoperiods. Different asymmetrical skeleton photoperiods and seasonal scotophase scans indicate (1) that light entrains endogenous circadian rhythms (ECR) of photosensitivity and the position of the photoinducible phase shifts according to the length of the basic photoperiod, (2) a seasonal variation in response to asymmetrical skeleton photoperiods, and (3) dissociation in the two gonadotrophins LH and FSH and a possibility of two distinct ECRs of photosensitivity for LH and FSH. Annual phasing of the ECRs of photosensitivity of the two gonadotrophins and/or interaction of hormones might be involved in the seasonal reproduction and photosensitivity of this bird.