Size regulation of double and half embryos in the mice musculus

Genetic chimeras made by aggregating early mouse embryos have many uses in developmental biology and have also provided insights into embryonic growth regulation. There is an indication that the embryo can regulate for an increase in size because although aggregation chimeras are twice as big as normal embryos when made, they are born of normal size. Upward regula..... tion of size reduced embryos is also possible. Half embryos made by the isolation or destruction of one of the blastomeres of a 2-cell embryo are also born of normal size. Little is known about the timing or the mechanism of this size regulation. In this study, the timing of size regulation in double and half embryos was clearly established by comparison of cell numbers derived from serial reconstruction of light microscope sections of control and experimental embryos. It was shown that size regulation in double embryos occurred around 6dl6h and in half embryos by 7dOh. Size regulation occurred in all tissues at the same time indicating a single control mechanism for the entire embryo. More detailed examination of the growth of double embryos revealed that size regulation occurred by alteration in cell cycle length~ No excessive cell death was found in double embryos compared to the controls and continuous labelling with [3H] thymidine showed no large non-dividing cell population in double embryos. However, a comparison of the mitotic index of double and control embryos after colcemid treatment, revealed a large difference between the two around 5dl6h to 6d16h. During this period, control embryos underwent a proliferative burst not shown by the double embryos. The mechanism for cell cycle control is not clear; it may be intrinsic to the embryo or determined by the uterine environment. Evidence was found suggesting that differentiation in the postimplantation embryo was cell number dependent. The timing of differentiative events was examined in half, double and control embryos. Proamnion formation, which occurs prior to size regulation, occurs at the same cell number but at different times in the three groups of embryos. However mesoderm which appears after size regulation was seen at the same time in all grollps of embryos.

The Importance and achievement of work values and locus of control as factors in work motivation

The present research study examined the relationships in a work motivation context among perceived importance and achievement of work values, locus of control and internal work motivation. The congruence of a work value was considered to be the discrepancy between the importance of a work value and the perceived achievement of that value. The theoretical framework utilized was based on a self-perpetuating cycle of motivation which included the perceived importance and achievement of work values and internal work motivation as separate and distinct, yet interrelated factors. It was hypothesized that individuals who experienced high congruence of work values would experience higher levels of internal work motivation than individuals who had low congruence of work values. It was also hypothesized that individuals who had an internal locus of control would experience more internal work motivation individuals well, the and have higher congruence of work values than who had an external locus of control. As possibility of locus of control as a moderator between importance of work values and internal work motivation was explored. Survey data were collected from 184 managerial level employees of the XYZ company during an ongoing training session. The following instruments were employed to measure the variables: Elizur's (1984) Importance of Work Values, Hunt and Saul's (1985) Achievement of Work Values, Hatfield, Robinson and Huseman's (1975) Job Perception Scale, a modified version of Rotter's (1966) I-E Locus of Control Scale and the Internal Work Motivation Scale (Hackman & Oldham, 1980) which is a part of the Job Diagnostic Survey. The findings indicated that locus of control was not a significant factor in determining congruence between work values or internal work motivation for this sample. Furthermore, locus of control was also found not to be a moderator between the importance of work values and internal work motivation. All individuals in this study had relatively high levels of internal work motivation. However, individuals who had higher congruence of work values did have significantly higher internal work motivation than those who had low congruence of work values for a majority of the 21 values. This was particularly true for the intrinsic values which included responsibility, meaningfulness and use of abilities. In addition, the data were analysed into a hierarchy of needs to indicate possible organizational development or human resource development needs for the XYZ corporation.