Melanocytes in Human Embryonic and Fetal Skin: A Review and New Findings

Melanocytes account for approximately 5–10% percent of the cells in adult epidermis. Unlike the ectodermally derived keratinocytes, they originate in the neural crest and migrate into the epidermis early in development. There has been an interest in melanocytes in developing human skin since the late 1800s, when concentrated pigmented cells were identified in the sacro-coccygeal skin of Japanese fetuses. This observation led to speculation and subsequent investigation about the racial nature of the melanocytes in this site (the Mongolian spot), the presence of melanocytes in fetuses of other races, the timing of appearance of these cells in both the dermis and epidermis, and their origin. The early investigators relied primarily on histochemical methods that stained either the premelanosome or the pigmented melanosome, or relied upon the activity of tyrosinase within the melanosome to effect the DOPA reaction. Studies by electron microscopy added further documentation to the presence of melanocytes in the skin by resolving the structure of the melanosome regardless of its state of pigmentation. All of these methods recognized, however, only differentiated melanocytes. The thorough investigations of melanocytes in the skin from a large number of black embryos and fetuses by Zimmerman and colleagues between 1948 and 1955 provided insight into the time of appearance of melanocytes in the dermis (10–11 weeks' menstrual age) and the epidermis (11–12 weeks) and revealed the density of these cells in both zones of the skin of several regions of the body. The precise localization of the melanocytes in the developing hair follicles was contributed by the studies of Mishima and Widlan (J Invest Dermatol 1966; 46:263–277). More recently, monoclonal antibodies have been developed that recognize common oncofetal or oncodifferentiation antigens on the surface or in the cytoplasm of melanoma cells and developing melanocytes (but not normal adult melanocytes). These antibodies recognize the cells irrespective of the presence or absence of melanosomes or their activity in the synthesis of pigment and therefore are valuable tools for re-examining the presence, density, and distribution patterns of melanocytes in developing human skin. Using one of these antibodies (HMB-45), it was found that dendritic melanocytes are present in the epidermis between 40 and 50 days estimated gestational age in a density comparable with that of newborn epidermis and are distributed in relatively non-random patterns. A number of questions about the influx of cells into the epidermis, potential reservoirs of melanoblasts retained within the dermis, division of epidermal melanocytes, and the interaction of melanocytes and keratinocytes during development remain unresolved. The tools now appear to be available, however, to begin to explore many of these questions.     

The Action of Mercaptoethanol on Cell Division in Synchronized Tetrahymena1

SYNOPSIS. Action of mercaptoethanol (ME) on cell division and macromolecular synthesis was examined in Tetrahymena synchronized for division. Cells continuously exposed to increasingly higher concentrations of ME divided with progressively longer division delays showing a dosage-dependent response to the agent. Division was blocked in 2 × 10^?2 M ME. Many cells cytolyzed in high concentrations of ME (4 × 10^?2 M); others became spherical and motility decreased. Non-delaying concentrations of ME (2 × 10^?2 M) had little or no effect on protein synthesis but decreased DNA and RNA synthesis 10 and 35%, respectively. Blocking concentrations inhibited incorporation of phenylalanine, thymidine and uridine 35, 60, and 85%, respectively. It is suggested that the mode of action of ME is mediated thru inhibition of macromolecular synthesis essential for cell division and thru inhibition of formation of disulfide bridges between protein subunits.     

Planktonic bloom-forming Cyanobacteria and the eutrophication of lakes and rivers

SUMMARY. 1. Eutrophication of water bodies involves the enrichment of plant nutrients, often followed by significant shifts in the phytoplankton towards Cyanobacteria. When comparing different aquatic systems, even with similar nutrient contents and in the same climatic region, inverse deductions are not valid; i.e. (a) the presence of Cyanobacteria does not necessarily indicate eutrophic conditions, or (b) eutrophic or even poly-trophic conditions do not necessarily support cyanobacterial development.
2. Above a threshold of 10 μg 1⁻¹ total phosphorus, the development of Cyanobacteria can be described by physical factors, such as water column stability. By characterizing different forms of turbulence, the presence or absence of Cyanobacteria in lakes and rivers can be predicted.
3.When the turbulence of the water column is rather low, as it is in sheltered or meromictic lakes, Cyanobacteria can build up dense populations. In nutrient poor systems, species of Oscillatoria and (seldom) Aphanizomenon are dominating.
4.If the turbulence of the water column is high (mixing depth much greater than euphotic depth) or the mixing pattern is irregular, as in slowly flowing or regulated rivers, Cyanobacteria are outcompeted.
5. In the presence of frequent or permanent turbulence, but with mixing depths lower or not much greater than the euphotic zone (as it is the case in shallow, unstratified lakes, mostly eutrophic or even hypertrophic), Cyanobacteria can outgrow normally dominant r -strategists under conditions of low N:P ratios, high water temperatures, pH >9.0 or low light availabilities.
6. If turbulence is comparatively great (10 to $15 m) and stable for a longer period of time, some cyanobacteria are able to adapt.
7. Our statements are discussed on the basis of physiological characteristics.     

Printed in Great Britain Mandobius regalis gen. et sp.n. (Copepoda: Poecilostomatoida: Lichomolgidae) associated with the coral Pectinia lactuca in New Caledonia

A new genus, Mandobius gen.n, containing a new species, M. regalis sp.n., is associated with the coral Pectinia lactuca in New Caledonia. The new copepod differs conspicuously from the allied genus Paramolgus in having only one seta on the first segment of the first antenna, in the formula 1,11,3 for the third segment of the endopodite of leg 1, and in the formula 11,1,5 for the third segment of the exopodite of leg 4.     

Interspecific competition in Drosophila I. Reversal of competitive superiority due to varying concentration of ethanol

The experiments reported here were designed to investigate the outcome of interspecific competition between Drosophila melanogaster and D. simulans in environments varying in one factor only. The factor chosen was ethanol concentration in the medium; the strains used were D. melanogaster SM5 (Series I), D. melanogasterw, b , (Series II) and D. simulans v (both Series).
The results of competition over a number of generations, the longest experiment lasting 100 days, showed clear differences in the relative competitive abilities of the two species between the different environments. With no ethanol, D. simulans won in all replicates; with 896 ethanol, D. melanogaster won in all replicates; at intermediate (496) concentration, the winning species was not consistent. Experiments in Series II showed very similar results to their counterparts in Series I despite distinct genetic differences between the strains of D. melanogaster used.
These results tie in with published work, on (i) the relative susceptibility of single–species cultures of D. melanogaster and D. simulans to high ethanol concentrations, and (ii) distributional patterns observed in some field populations exposed to alcohols in their environment.     

Segment number,body length,and latitude in geophilomorph centipedes: a ‘converse‐Bergmann’ pattern

There is a negative relationship between trunk segment number and latitude among geophilomorph centipedes in general. A similar relationship is known to exist within the most intensively‐studied geophilomorph species, Strigamia maritima, and also within several other species from this group. Previously, it was considered that this relationship did not involve body length; instead, individuals of S. maritima with more segments were considered to be more finely subdivided (not longer) than those with fewer segments. This incorrect interpretation arose from the difficulty of reliably separating post‐embryonic stages and thus of making a simple and direct comparison. In the present study, we build on recent work that facilitates such comparisons; and we show conclusively that individuals with more segments are longer. Our finding means that it is now possible to connect the work on S. maritima in particular, and on geophilomorph centipedes in general, with the debate about Bergmann's ‘rule’: the proposal that body size increases with increasing latitude. There is a clear ‘converse‐Bergmann’ pattern, as has been found in several other taxa. We propose an adaptive hypothesis that may explain why geophilomorphs show this pattern. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.