Mendel, the empiricist

In contemporary texts in biology and genetics, Mendel is frequently portrayed as a theorist who was the father of classical genetics. According to some authors, he created his theory of inheritance to explain the results of his experimental hybridizations of peas. Others have proposed that he designed and carried out his experiments to demonstrate the correctness of a theory of inheritance he had already developed. We disagree strongly with these views of Mendel. Instead, we have come to regard him as an empirical investigator trying to discover the empirical natural laws describing the formation of hybrid peas and the development of their offspring over several generations. We have supported our view with an analysis of portions of Mendel's paper and his letters to Carl N ageli.     

Identified taste bud cell proliferation in the perihatching chick [published erratum appears in Chem Senses 1998 Aug;23(4):459]

Developing taste buds in the anterior mandibular floor of perihatching chicks were studied by high voltage electron microscopic autoradiography in order to identify proliferating gemmal cell types. Montaged profiles of 29 taste buds in five cases euthanized between embryonic day 21 and posthatching day 2 were analyzed after a single [3H]thymidine injection administered on embryonic day 16, 17 or 18. Results showed that dark cells comprised 55% of identified (n = 900 cells) and 62% of labeled (n = 568 cells) gemmal cells as compared with light, intermediate, basal or perigemmal bud cells. Dark cells had both a greater (P < 0.05) number of labeled cells and a greater amount of label (grains/nucleus) than the other four bud cell types, irrespective of injection day. The nuclear area (micron 2) of dark cells was not significantly larger (P > 0.05) than that of the other gemmal cell types and therefore cannot account for the greater amount for label in the dark cells. Interestingly, only dark cells showed a positive correlation (P < 0.003) between amount of label and nuclear area. Results suggest that, during the perihatching period of robust cell proliferation, dividing dark cells may give rise primarily, but not exclusively, to dark cell progeny.      

Growth and development of the human infant breast.

Seventy-two samples of infant breasts, aged from newborn to 2 years, were collected at necropsy. Whole-mount preparations and histological sections were made. A system of classification was devised to study the extent of the structural development of the ductal system (morphological types I, II, and III) and the functional differentiation of the lining epithelium (functional stages I to V). There was no correlation between the age of the infant and the type of development of the ductal system. In contrast, the epithelial differentiation followed a chronological pattern, starting with secretory changes and apparently going through a period characterized by apocrine metaplasia before post-secretory involution. These epithelial changes were not associated with the morphological type of the ductal system. There were no distinguishing features between the breasts from the two sexes. Immunoperoxidase staining for actin and kappa-casein was carried out to study the myoepithelial cells and secretory cells, respectively. Myoepithelial cells were present at all stages and prominent staining for casein was observed up to 2 months of age. Embryonic-type adipose tissue was seen in 7 cases, in one of which it was associated closely with the developing ductal system. Extramedullary hematopoiesis was observed in the periductal connective tissue until 4 months of age. This paper describes the most extensive anatomical and histological study of the human infant breast to date and lays the foundation for a detailed study of the epithelial and stromal changes that take place during human breast development.     

The metaphase-arrest technique applied to human cervical epithelium. I. Technique and dose-response studies

In order to study cell proliferation in intact human cervical epithelium, a technique involving metaphase arrest has been utilized. Metaphase accumulation is observed following intraepithelial administration of vincristine sulphate, at a predetermined optimum dose of 50 micrograms/ml. A significant delay before the onset of stathmokinetic activity is demonstrated; thereafter linearity of accumulation is apparent over a 4-hr period following injection. The technique appears applicable to the estimation and comparison of cell production rates in vivo of normal cervical epithelium, cervical intraepithelial neoplasia, wart-affected cervical epithelium and early invasive carcinoma. However, individual values are likely to be imprecise in isolation, indicating the need to study relatively large numbers of subjects in each group. Some practical difficulties are discussed.     

The distribution of [3H]kainate binding sites in primate hippocampus is similar to the distribution of both Ca2+-sensitive and Ca2+-insensitive [3H]kainate binding sites in rat hippocampus

The distribution of [³H]kainate binding sites was determined by quantitative autoradiography in three vertebrate species: rat, monkey, and human. These animals displayed a similar pattern of binding site density in the hippocampus. Highest levels were found within the stratum lucidum and moderate levels in the inner portion of the dentate gyrus molecular layer. Although the distribution is similar, there is a lower density of binding sites in the stratum lucidum of primates than in rodents. Experiments using rat brain synaptic plasma membrane fractions indicated that inclusion of Ca²⁺ ions results in a selective reduction in binding at the high affinity sites. The Ca²⁺-inhibited and Ca²⁺-insensitive binding sites in the rat hippocampus exhibited a similar distribution. Together, these results suggest that in a variety of mammalian species kainate receptors exhibit similar regional distributions, and that the high anf loe affinity kainate binding sites also exhibit similar regional distributions.Special Issue dedicated to Prof. Eduardo De Robertis.     

Distribution and synthesis of type V collagen in the rat mammary gland

In the 100-day-old virgin and lactating rat mammary glands, type V collagen is mainly present in the interstitial connective tissue and in association with blood vessels. It is not present in the basement membrane region surrounding the ducts in mature virgin glands but is present in this region in neonatal and lactating glands. Ultrastructural localization of type V collagen reveals that it is mainly located on the basal surface (i.e., the surface in contact with the basement membrane) of epithelial but not myoepithelial cells. In addition, type V collagen is located on some interstitial collagen fibers and on a large number of granules that are in close proximity to the basal surface of both epithelial and myoepithelial cells. Immunofluorescence and biochemical studies indicate that several clonal mammary fibroblastic cell lines synthesize type V collagen in vitro. In some cell lines, type V collagen is secreted as an extensive fibrillar meshwork on the surface of the cells, whereas in other cell lines, it is secreted beneath the cells around their periphery. A number of mammary epithelial and myoepithelial-like cells, however, do not synthesize type V collagen in vitro.     

Microbial transformation ofN-heptyl physostigmine,a semisynthetic alkaloid inhibitor of cholinesterase

The microbiological transformation ofN-heptyl physostigmine (L-693, 487) (1), a semisynthetic physostigmine cholinesterase inhibitor, was investigated usingVerticillium lecanii MF 5713 (ATCC 74148),Acremonium sp MF 5723 (ATCC 74164) andActinoplanes sp MA 6559 (ATCC 53771). Nine microbial metabolites (2–10) of 1 were isolated and purified using reversed-phase HPLC. The structures of the metabolites were established using spectroscopic techniques including MS and NMR. Some of the microbial metabolites were identical to metabolites present in urine of a dog treated with 1.