Differentiation of Reproductive Cells in Volvox carteri*

SYNOPSIS. The life cycle of Volvox carteri was studied in axenic culture using the NB-3 and the NB-7 strains isolated from Nebraska. Vegetative colonies of both strains contain 8–12 asexual reproductive cells (gonidia) which divide to form daughter colonies. During daughter colony formation, the reproductive cells of the daughters are delimited at an early stage of cleavage. Gonidia are delimited at the division from 16 to 32 cells, but eggs and male initial cells are not differentiated until the division of the 32-celled stage. In all instances the reproductive cells are the products of unequal cleavages. Male and female colonies are formed in separate clones. Female colonies contain approximately 20 eggs. Male colonies have approximately 50 male initial cells, each of which forms a sperm bundle containing 64 or 128 sperm. Sperm bundles penetrate female colonies and fertilize the eggs. Zygote formation, zygote germination, and the development of gone colonies is described. Sexual type was inherited in a 1:1 ratio. Male colonies appear spontaneously in the male strain, but female colonies were formed in the female strain only in the presence of a substance produced by colonies from male cultures. This female inducing substance is produced in male cultures primarily, if not exclusively, by male colonies rather than by vegetative colonies. The female inducing substance is heat labile and non-dialyzable. Activity is destroyed by Pronase, but not by trypsin, chymotrypsin or ribonuclease. Gonidia appear to be most susceptible to female induction during the early stages of their expansion prior to cleavage.     

Temperature Effect on the Photo-Accumulation and Phobic Response of Volvox aureus*

SYNOPSIS. The effect of temperature on photoaccumulation and photophobic response of Volvox aureus were studied. The algae exhibited positive photoaccumulation at room temperature and negative at low temperature. When stimulated with light of intermediate intensiy (～ 5 × 10³ lux), the phobic response of the algae consisted of a decrease in the frequency or the cessation of flagellar movement in the anterior cells. At room temperature, an increase in light intensity elicited the phobic response, whereas at low temperature a decrease in light intensity was the effective stimulus. The phobic response lasted only a few seconds. The positive and negative photoaccumulations of the algae could be explained by the brief cessation of flagellar movement in the anterior cells, elicited by an increase of stimulus light at room temperature or a decrease of stimulus at low temperature.     

Bakteriensymbiose bei Volvox aureus Ehrenberg

Ohne ZusammenfassungDissertation der Mathematisch-Naturwissenschaftlichen Fakultät der Universität Tübingen.     

Flagellar Activity of the Colony Members of Volvox aureus Ehrbg. during Light Stimulation*

SYNOPSIS. The flagellar behavior of the colonial Volvox aureus Ehrbg. was examined by placing 1.01 μ polystyrene particles in suspension with Volvox, and recording particle movement photomicrographically. When directional light stimulation was given, flagellar activity ceased in the anterior cells of the stimulated side. Such responses create unequal driving forces on the 2 sides of the colony, so that the colony turns toward the stimulated side. Dose response studies indicated a photoresponse gradient from front to rear in the colony, anterior cells being most responsive. The mechanism of gradient formation has yet to be determined.     

Differentiation of germinal and somatic cells in Volvox carteri

Volvox carteri is a spherical alga with a complete division of labor between around 2000 biflagellate somatic cells and 16 asexual reproductive cells (gonidia). It provides an attractive system for studying how a molecular genetic program for cell-autonomous differentiation is encoded within the genome. Three types of genes have been identified as key players in germ-soma differentiation: a set of gls genes that act in the embryo to shift cell-division planes, resulting in asymmetric divisions that set apart the large-small sister-cell pairs; a set of lag genes that act in the large gonidial initials to prevent somatic differentiation; and the regA gene, which acts in the small somatic initials to prevent reproductive development. Somatic-cell-specific expression of regA is controlled by intronic enhancer and silencer elements.     

Sexual induction in Volvox carteri f. nagariensis by aldehydes

Summary Sexual induction in the Gone 12 mutant of Volvox carteri can be achieved by shortterm treatment with glutardialdehyde or formaldehyde, followed by capture of the aldehyde by means of amino acids at slightly acidic pH. The same effect is obtained by exposure to anthranilic acid formalide, the condensation product of 2-amino benzoic acid with formaldehyde, at low concentration for several minutes. This is in contrast to the prolonged exposure required by the specific glycoprotein inducer. In both situations the asexual reproductive cells are affected in such a way that they change their pattern of cleavage to form sexual embryos rather than asexual ones. Thus, besides the natural messenger molecule, a physical (UV light, heat) or molecular shock may trigger the chain reaction leading to expression of sexual induction.     

Sexual Differentiation of Gonadotropin Patterns

The original experiments, done by Witschi and his associates,on sexual differentiation of pituitary gonadotropins weie interpietedas demonstrating the contrasting effects of testes on the subsequentoutput of luteimzing hormone (LH) and interstitial cell stimulatinghormone (ICSH). The subsequent demonstration that these twohormones were identical has led to a theory that testes alterthe hypothala mic centeis which control the cyclic release ofLH "Masculinization of the female hypothalamic pituitary axishas been claimed following neonatal treatment with steroids".However, true sex reversal of gonadotiopin patterns has neitherbeen demon stiated, the male pattern has not yet been clearlydenned Consistent high levels of blood and pituitary folliclestimulating hormone (FSH) appear to be at least two characteristicsof the male pattern, and neither can be induced in lemales byneonatal treatment with testosterone propionate. Furthermore,castration of males at bnth with concomitant ovanan implinldtion,does not appear to remove the male pattern of high FSH. Consideringthat we understand so little regarding gonadotropin patternsin males, we cannot assume that this pattern can be inducedsimply by pie or postnatal steroid trealment. Considerably moredata on the positive and negative feedback effects of steroids,and steroid combinations, on TSH, LH, and piolictin in bothmales and females, will be requned before a meaningful conceptof sexual differentiation cin be formulated     

Genetic Control of Sexual Differentiation in Humans

The current literature results on genetic control of sex differentiation and morphogenesis of the human reproductive system are reviewed. Several examples of the nosologic forms caused by mutations in the genes analyzed are considered.     

Sexual pheromone induces diffusion of the pheromone-homologous polypeptide in the extracellular matrix of Volvox carteri

The C-terminal domain of pherophorin II is homologous to the sexual pheromone of Volvox carteri and is released from other domains during sexual induction. Green fluorescent protein fused to the C terminus of pherophorin II was located at the extracellular matrix directly surrounding the gonidium, the final target of the sexual-induction signal.     

Neuroendocrine Systems and Avian Sexual Differentiation

Sexual differentiation of the endocrine and behavioral componentsof the avian reproductive system occurs throughout embryonicdevelopment, initiating some of the early cellular events thatform the central nervous system (CNS) and culminating in theorganization of male or female neuroendocrine responses. Earlycellular events have been studied intensively in recent yearsand these developmental processes appear to involve specificgrowth factors in the development of certain tissues. Subsequentto cellular differentiation, primordial germ cells migrate tothe appropriate anatomical location and contribute to the developmentof the single ovary or testes; steroidogenesis begins soon thereafter.Other portions of the hypothalamo-pituitary-gonad (HPG) axisalso appear during early embryonic development with migrationof the gonadotropin-releasing hormone (GnRH) neurons from theolfactory region of the CNS to the midbrain and separate formationof the pituitary gland. The gonadal steroid hormones affectdevelopment of accessory sex structures as well as the laterorganization of neuroendocrine regulatory systems and secondarysex characteristics. Manipulation of steroids during embryonicand early posthatch periods results in altered endocrine andbehavioral responses in adult birds. There are marked speciesdifferences in the timing of these events, especially when precocialand altricial species are compared. Altricial species hatchin a less developed state and as such are more dependent onparental care. Of necessity, the precocial species must be capableof feeding and other motor capabilities at hatch and coincidentallytheir other physiological systems also appear to be more matureat this time. Finally, there is the separate issue of song birdsversus those avian species that do not have elaborate learnedsongs. It appears that most of the species with elaborate neuralcircuitry responsible for song are altricial. This may benefitthem from the standpoint of gaining more time and contact withthe parents to enable them to learn the appropriate song. Thereare also hormonal and neuroendocrine components critical inthe process of song development. Finally, the effects of environmentalfactors, such as endocrine disrupting chemicals take on addedsignificance when viewed in the context of exerting permanentorganizational effects which are likely to alter endocrine andbehavioral components of reproduction in the adult     

The Distribution of Daughter Colonies and Cell Numbers in a Natural Population of Volvox aureus Ehrenb

The distribution of cell numbers and daughter colonies was determinedin a population of Volvox aureus from Malham Tarn, North Yorkshireduring summer and autumn. The following ranges were recorded:cell number, 272–2340; colony diameter, 174–520µm; daughter colony number, 2–10 (mode 6). Culturedmaterial gave significantly higher values than these. A strongpositive correlation was found between cell number per colonyand the number of asexual daughters but no correlation was foundbetween the number of daughters and mother colony diameter. The results are discussed with reference to the theoreticalpacking of spheres, which the daughters approximate. The numberof daughters and their size upon liberation was also consideredin relation to grazing pressures and the relative loss of cellscaused by the disintegration of the mother colony. The mostsignificant factor was considered to be the size of the mothercolony which is probably controlled by nutrient supply and temperature. Volvox cell number, daughter colonies